1.         J. Akimitsu, M. Uehara, M. Ogawa, H. Nakata, K. Tomimoto, Y. Miyazaki, H. Yamane, T. Hirai, K. Kinoshita, and Y. Matsui

            "Superconductivity In The New Compound (Y1-Xcax)0.95sr2.05cu2.4(Co3)0.6oy"

            Physica C 201 (3-4), 320-324 (1992).

 

            ABSTRACT: A new Cu-oxide superconductor (Y1-xCax)0.95Sr2.05Cu2.4(CO3)0.6Oy has been found by resistivity and magnetization measurements. The transition temperature is about 63 K. The crystal structure consists of the periodic replacements of the Cu(I) site with a CO3 group in the basic YBa2Cu3Oy structure.

 

2.         H. Asahi, S. J. Yu, J. Takizawa, S. G. Kim, Y. Okuno, T. Kaneko, S. Emura, S. Gonda, H. Kubo, C. Hamaguchi, and Y. Hirayama

            "Ingaasp/Inp Quantum Wires Fabricated By Focused Ga Ion-Beam Implantation"

            Surf. Sci. 267 (1-3), 232-235 (1992).

 

            ABSTRACT: InGaAsP/InP quantum-wire structures are fabricated by focused Ga ion beam implantation onto InGaAs/InP single quantum well (QW) structures. It is found that InGaAsP layers produced by the intermixing of InGaAs/InP QW's by Ga ion implantation and subsequent thermal annealing are nearly lattice matched to the InP substrate. Fabricated quantum-wire structures exhibit photoluminescence spectra showing a large blue shift, which is induced by the carrier confinement into wire structures and the change of well composition.

 

3.         J. L. Chern, K. Otsuka, and P. Mandel

            "Effects Induced By Transit-Time On A Coupled 2-Element Optical Bistable Device"

            IEEE J. Quantum Electron. 28 (2), 555-561 (1992).

 

            ABSTRACT: In this paper, we study the effects of finite transit time, i.e., delay, on dynamics in a coupled two-element optical bistable device. Here finite transit time is considered because of signal propagation between the elements. It is shown that delay can be used as a measure of crosstalk between the coupled elements and it will increase the "lethargy time." Thus, many interesting, transient phenomena take place both in hysteresis and pitchfork (symmetry-breaking) regimes. Symmetry-recovering crisis originating from the collision between the unstable periodic orbit and chaotic asymmetrical solution is predicated to occur for T almost-equal-to-tau (T: transit time, tau: response time of nonlinear medium). It is shown that symmetry-recovering crisis results in switching failure in set-reset (S-R) flip-flop operations with pitchfork bifurcation structure.

 

4.         R. Cingolani, M. Lepore, R. Tommasi, I. M. Catalano, H. Lage, D. Heitmann, K. Ploog, A. Shimizu, H. Sakaki, and T. Ogawa

            "2-Photon Absorption In Gaas Quantum Wires"

            Phys. Rev. Lett. 69 (8), 1276-1279 (1992).

 

            ABSTRACT: We have investigated the polarization-dependent two-photon absorption in GaAs/AlGaAs quantum wires. The anisotropic selection rules of the multiphoton absorption process are exploited to study the one-dimensional 2p exciton states and the transitions between quantum wire subbands of different quantum numbers (DELTA-n(y) not-equal 0 selection rule). The deviations from the selection rules derived for the strict one-dimensional case are discussed, and depend on the actual quasi-one-dimensional character of the excitonic wave functions.

 

5.         K. W. Delong and J. Yumoto

            "Chirped Light And Its Characterization Using The Cross-Correlation Technique"

            J. Opt. Soc. Am. B-Opt. Phys. 9 (9), 1593-1604 (1992).

 

            ABSTRACT: We analyze the Cross-correlation (SUM-frequency generation) method of chirp measurement of short light pulses. We find that there are two complementary methods to measure the chirp, depending on whether the pump has a larger temporal or spectral resolution than the pulse to be measured. We show how to relate these measurements of chirp to the time domain description for linear chirp. We also discuss the use of this method in measuring nonlinear chirps. We demonstrate experimentally the dependence of the results of the measurement on the spectral response function of the monochromator.

 

6.         S. R. Friberg

            "Optical Solitons For Signal-Processing"

            IEICE Trans. Fundam. Electron. Commun. Comput. Sci. E75A (1), 5-11 (1992).

 

            ABSTRACT: We consider applications of optical solitons to signal processing. Soliton switching devices promise ultrafast operation and compatibility with communications systems using optical pulses. Quantum soliton effects include broadband squeezing and quantum nondemolition measurements, and can reduce noise and increase sensitivities of optical measurements. We report the demonstration of two-color soliton switching and describe progress towards implementation of quantum nondemolition measurement of photon number using soliton collisions.

 

7.         S. R. Friberg

            "Optical Solitons For Signal-Processing"

            IEICE Trans. Electron. E75C (1), 3-9 (1992).

 

            ABSTRACT: We consider applications of optical solitons to signal processing. Soliton switching devices promise ultrafast operation and compatibility with communications systems using optical pulses. Quantum soliton effects include broadband squeezing and quantum nondemolition measurements, and can reduce noise and increase sensitivities of optical measurements. We report the demonstration of two-color soliton switching and describe progress towards implementation of quantum nondemolition measurement of photon number using soliton collisions.

 

8.         S. R. Friberg and K. W. Delong

            "Breakup Of Bound Higher-Order Solitons"

            Opt. Lett. 17 (14), 979-981 (1992).

 

            ABSTRACT: Bound higher-order solitons, sometimes called breather solitons, can easily be broken apart by small perturbations. We discuss the conditions for breakup of bound solitons and describe a method to determine the details of the soliton breakup. Using this method, we illustrate the breakup of bound solitons by optical filters, by asymmetric FM modulation (not AM or symmetric FM modulation), and by superposition with other optical pulses.

 

9.         S. R. Friberg, S. Machida, and Y. Yamamoto

            "Quantum-Nondemolition Measurement Of The Photon Number Of An Optical Soliton"

            Phys. Rev. Lett. 69 (22), 3165-3168 (1992).

 

            ABSTRACT: We report the quantum-nondemolition measurement of the photon number of an optical soliton. Taking advantage of the conservation properties of quantum solitons, we were able to read out the photon number of a "signal" soliton via the phase of a "probe" soliton after a soliton collision in a single-mode low-loss optical fiber. Subsequent noise measurements showed the photon number fluctuations of the signal soliton at the shot-noise limit to be correlated to the phase fluctuations of the probe soliton, signifying a backaction-evading measurement of the photon number.

 

10.       M. Fujiki

            "Structural Defects In Poly(Methylphenylsilylene)"

            Chem. Phys. Lett. 198 (1-2), 177-182 (1992).

 

            ABSTRACT: The Si-based structural defects in poly(methylphenylsilylene) backbones were detected as two new Si-29 NMR signals and as two new Si-Si vibrational IR bands. The defects, consisting of an organosilyne unit and about three methylphenylsilylene monomer units near the branch, were presumed to be in a fairly lengthened Si-Si bonding state. The empirical linear relationship between the relative intensity of broad photoluminescence and the defect density predicts the disappearance of the broad luminescence for a defect density of less than 1 %.

 

11.       M. Fujino, T. Hisaki, M. Fujiki, and N. Matsumoto

            "Preparation And Characterization Of A Novel Organopolysilane - (3,3,3-Trifluoropropyl)Methylpolysilane"

            Macromolecules 25 (3), 1079-1083 (1992).

 

            ABSTRACT: The first soluble (fluoroalkyl)polysilane high polymer was prepared by a conventional Wurtz-type reaction of dichlorosilane and sodium in n-paraffins above 150-degrees-C. The structure of this polymer was determined by elemental analyses (C and H), gel permeation chromatography, and spectral analyses [FT-IR, FT-NMR (H-1, C-12, F-19, and Si-29), and UV]. The molecular weight distribution of the polymer was monomodal, and the weight-average molecular weight of this polymer was 31 000. The UV absorption maximum due to Si catenation was at 285 nm. This is the shortest wavelength yet reported for an organopolysilane high polymer. The thermochromic behavior of this polymer was also observed in the solid state at temperatures from -120 to + 100-degrees-C. The polymer began to decompose at around 200-degrees-C, and its glass transition temperature was -3-degrees-C, which was higher than that of the nonfluorinated polymer.

 

12.       Y. K. Fukai, S. Tarucha, Y. Hirayama, Y. Tokura, and T. Saku

            "Reflection And Refraction Of Ballistic Electrons Through Different Carrier Concentration Regions"

            Appl. Phys. Lett. 60 (1), 106-108 (1992).

 

            ABSTRACT: Transmission and reflection characteristics of ballistic electrons are studied in a macroscopic four-terminal square device with a strip Schottky gate placed so as to bisect the device. Since the gate is negatively biased, a bend resistance peak at zero magnetic field, which is induced by ballistic electron injection into an opposite voltage probe, varies from positive to negative, and a magnetic focusing peak shifts to a lower field. These phenomena arise from the reflection of ballistic electrons crossing regions of different electron densities. The transmission and reflection probabilities are determined as a function of gate voltage, and are related to the change in the refractive index of ballistic electrons.

 

13.       T. Fukui and S. Ando

            "Gaas Tetrahedral Quantum Dots Grown By Selective Area Mocvd"

            Superlattices Microstruct. 12 (2), 141-144 (1992).

 

            ABSTRACT:

14.       T. Fukui, S. Ando, T. Honda, and T. Toriyama

            "Gaas Tetrahedral Quantum Dot Structures Fabricated Using Selective Area Mocvd"

            Surf. Sci. 267 (1-3), 236-240 (1992).

 

            ABSTRACT: New GaAs quantum dot structures, called tetrahedral quantum dots (TQD's), are proposed to make a zero-dimensional electron-hole system. The TQD's are surrounded by crystallographic facets fabricated using selective area MOCVD on GaAs(111)B substrates. The calculated energy sublevel structures of zero-dimensional electrons in a GaAs TQD show large quantum size effects, because electrons are confined three-dimensionally. GaAs and AlGaAs tetrahedral facet structures were grown using MOCVD on GaAs(111)B substrates partially etched into a triangular shape. Tetrahedral growth with {110} facets occurs in the triangular areas. The cathodoluminescence intensity map for GaAs tetrahedrons buried in AlGaAs shows the tetrahedral dot array.

 

15.       T. Fukui, H. Saito, M. Kasu, and S. Ando

            "Mocvd Methods For Fabricating Gaas Quantum Wires And Quantum Dots"

            J. Cryst. Growth 124 (1-4), 493-496 (1992).

 

            ABSTRACT: Semiconductor low-dimensional structures such as quantum wires and quantum dots fabricated by metalorganic chemical vapor deposition (MOCVD) are reported. GaAs/AlAs quantum wire arrays including fractional-layer superlattices were grown on (001) GaAs vicinal surfaces. Uniform lateral superlattices were observed by transmission electron microscopy. However, polarization-dependent photoluminescence and the optical absorption spectra suggest that significant alloying occurs in AlAs/GaAs vertical interfaces. GaAs tetrahedral quantum dots buried in AlGaAs were also fabricated on a SiO2 masked (111)B GaAs substrate partially etched to a triangular shape. First, AlGaAs truncated tetrahedral structures with three {110} facets were grown on GaAs triangular areas. Next, GaAs dot structures were sequentially grown on top of the AlGaAs truncated tetrahedron. Finally, AlGaAs was over-grown on {110} sidewall facets with a different growth condition. We observed large quantum size effects for about 100 nm TQD in low temperature photoluminescence, which is in good agreement with calculations.

 

16.       T. Fukui, K. Tsubaki, H. Saito, M. Kasu, and T. Honda

            "Fractional Superlattices Grown By Mocvd And Their Device Applications"

            Surf. Sci. 267 (1-3), 588-592 (1992).

 

            ABSTRACT: (AlAs)1/2(GaAs)1/2 fractional-layer superlattices (FLS's) are grown on (001) vicinal substrates by metalorganic chemical vapor deposition. Various kinds of GaAs substrates were used. When the substrate is misoriented to [110] by 1.92-degrees and [110] by 0.10-degrees, uniform superlattice periods over a large surface area are observed by bright field transmission electron microscopy (TEM). The results suggest the ideal growth from a kink site occurs during MOCVD growth, and the distances between kink sites are equal. On a substrate misoriented to [110] by 1.90-degrees, the superlattice periods exhibit an undulation. This shows that kink flow mode growth is not dominant in the [110] direction. On a substrate misoriented to [010] by 2.0-degrees, no superlattice periods were observed. From the above results, we discuss the growth mechanisms. Polarization dependent photoluminescence and optical absorption spectra of FLS's were also observed. Electron wave interference devices with lateral periodic potential were fabricated.

 

17.       K. Furukawa, M. Fujino, and N. Matsumoto

            "Cubic Silicon Cluster"

            Appl. Phys. Lett. 60 (22), 2744-2745 (1992).

 

            ABSTRACT: A cubic silicon cluster having eight bonds each terminated by a tert-butyl substituent, tert-butyloctasilacubane (TBOSC), is studied. TBOSC was formed and isolated by chemical procedures. The optical properties of TBOSC were measured in comparison with those of bulk silicon. TBOSC is purple and its absorption edge (lambda(g)) is observed at 650 nm (1.9 eV) at room temperature. This lambda(g) is 0.8 eV larger than that of bulk silicon. It also shows photoluminescence extending to 850 nm at 77 K although bulk silicon shows no photoluminescence.

 

18.       A. Furusaki, H. Takayanagi, and M. Tsukada

            "Josephson Effect Of The Superconducting Quantum Point Contact"

            Phys. Rev. B 45 (18), 10563-10575 (1992).

 

            ABSTRACT: The dc Josephson effect of a constriction in a two-dimensional superconductor-semiconductor-superconductor junction, i.e., a superconducting quantum point contact, is investigated theoretically for both long and short constriction lengths compared with the superconducting coherence length. It is shown that the critical current of a ballistic superconducting quantum point contact increases stepwise as a function of its width under appropriate conditions. The step height generally depends on both the superconducting energy gap and junction parameters. The effect of normal reflections at the superconductor-semiconductor interface is also examined.

 

19.       A. Furusaki and M. Ueda

            "Semiclassical Theory Of Small Josephson-Junctions - Solution Of The Master Equation"

            Phys. Rev. B 45 (18), 10576-10596 (1992).

 

            ABSTRACT: Within a semiclassical approximation and at the weak-coupling limit, where the charging energy dominates the Josephson coupling energy, the dynamics of small-capacitance superconducting tunnel junctions can be described by a stochastic master equation for the probability distribution of junction charges. We develop a method of solving this equation and obtain an analytic solution when Cooper-pair, quasiparticle, and Zener tunneling are all present under an arbitrary Ohmic conductance at zero temperature. We use this solution to systematically investigate the static and dynamic properties of small Josephson junctions. The charge distributions, current-voltage characteristics, and voltage spectra are analytically calculated and numerically evaluated for wide ranges of parameters. The separate contributions from quasiparticle and Cooper-pair tunneling to voltage spectra are evaluated and compared based on their respective sum rules. The linewidths of the resonance peaks for single-electron tunneling and Bloch oscillations are also discussed.

 

20.       A. Furusaki and M. Ueda

            "Exact Solution Of The Master Equation For Ultrasmall Normal Tunnel-Junctions"

            Phys. Rev. B 45 (7), 3435-3448 (1992).

 

            ABSTRACT: An exact solution for the stochastic master equation describing the semiclassical Coulomb-blockade theory is obtained for an arbitrary shunt resistance at zero temeprature. This solution is used to systematically evaluate various quantities characterizing the dynamics of single-electron-tunneling oscillations. Our solution provides analytic expressions of the voltage spectra and sum rules.

 

21.       Y. Hida, S. Imamura, and T. Izawa

            "Ring Resonator Composed Of Low-Loss Polymer Wave-Guides At 1.3-Mu-M"

            Electron. Lett. 28 (14), 1314-1316 (1992).

 

            ABSTRACT: A channel waveguide ring resonator was successfully fabricated using polymers synthesised from deuterated methacrylate and deuterated fluoromethacrylate. Resonance curves with a finesse of 14.8 and an extinction ratio of 0.83 were obtained at a wavelength of 1.3 mum. The corresponding waveguide loss was estimated to be 0.10 dB/cm. In addition, the temperature and polarisation characteristics of the resonance were investigated.

 

22.       Y. Hirayama

            "N-Type And P-Type Inplane Gated Field-Effect Transistors Directly Written On A Semiinsulating Gaas Substrate"

            Appl. Phys. Lett. 61 (14), 1667-1669 (1992).

 

            ABSTRACT: A new type in-plane gated field effect transistor where the semi-insulating substrate itself is used as a gate insulator region is proposed. n- and p-type in-plane gated field effect transistors are fabricated on a semi-insulating GaAs substrate by focused ion beam scanning of Si++ and Be++, respectively. These in-plane gated field effect transistors are found to operate well at room temperature.

 

23.       Y. Hirota, Y. Homma, and K. Sugii

            "Clean And Damage-Free Gaas-Surfaces Prepared By Ultrasonic Running Deionized Water-Treatment"

            Appl. Surf. Sci. 60-1, 619-624 (1992).

 

            ABSTRACT: GaAs(001) surfaces treated with ultrasonic running deionized water (URDIW), after being etched by H2SO4 or NH4OH were examined by using X-ray photoelectron spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED). XPS analysis revealed that the arsenic and gallium oxides on chemically etched surfaces were completely removed by the URDIW treatment. RHEED observation indicated that the H2SO4-etched GaAs surface shows a streaky (2 X 1) surface reconstruction pattern at 360-degrees-C and that the NH4OH-etched surfaces show a (2 x 4) surface reconstruction pattern at 310-degrees-C. These experimental results indicate that chemically clean GaAs surfaces with little damage can be produced by URDIW treatment and that the stoichiometry of a URDIW treated surface can be controlled by varying the etching solutions.

 

24.       T. Homma, H. Asai, T. Osaka, K. Takei, and Y. Maeda

            "Nmr-Study On Compositional Inhomogeneity In Electroless Deposited Conip Films For Perpendicular Magnetic Recording"

            Chem. Lett. (9), 1783-1786 (1992).

 

            ABSTRACT: Compositional inhomogeneity in electroless-deposited CoNiP films with perpendicular magnetic anisotropy was examined using the spin echo Co-59-NMR technique for the first time. The existence of a Co-rich component was observed which was thought to cause the formation of an hcp structure and produce high perpendicular coercivity, Hc(perpendicular-to). An increment in the Co-rich component by heat-treatment was also observed which might be an origin of the increase in Hc(perpendicular-to).

 

25.       Y. Homma, M. Suzuki, and H. Hibino

            "Step Band Structures On Vicinal Si(111) Surfaces Created By Dc Resistive Heating"

            Appl. Surf. Sci. 60-1, 479-484 (1992).

 

            ABSTRACT: DC-heating-induced step bunching is studied using vicinal Si(111) surfaces with different misorientation angles ranging from 1 to 10-degrees toward [112BAR] in an ultrahigh vacuum scanning electron microscope. Although the growth rate depends on the misorientation angle, the bunching structure basically grows in the same manner on the substrates misoriented from 1 to 8-degrees; faceting of the surface into (111) terrace regions and step band regions, and then expansion of terrace regions. The size of the initial facet structure correlates with the misorientation angle; the period of the structure is proportional to the misorientation angle. During heating, step band regions link up with each other forming very straight structures. Thus the surface with parallel step bands is the final form of the DC-heating-induced step bunching. The growth rate of the bunching on 1 and 2-degrees surfaces is much higher than on higher-misorientation-angle surfaces. On a 10-degrees misoriented surface no DC-heating-induced bunching was observed.

 

26.       K. Hono, Y. Maeda, J. L. Li, and T. Sakurai

            "Direct Evidence For Compositional Fluctuation In Sputtered Co-Cr Thin-Films"

            J. Magn. Magn. Mater. 110 (3), L254-L258 (1992).

 

            ABSTRACT: Nano-scale concentration fluctuations in sputtered Co-23 at% Cr magnetic thin films were analyzed by atom probe field ion microscopy (APFIM). The atom probe concentration depth profile obtained from the film which was deposited on the W tip at 200-degrees-C clearly showed that the composition fluctuated significantly. The concentration of the Cr enriched region was in the range of 30-40 at% Cr, while that of the Cr depleted region was in the range of 5-10 at% Cr. This result proves that compositional fluctuations are present inside the grains of the Co-Cr sputtered film as suggested by the TEM observation of the chrysanthemum-like pattern (CP) structure.

 

27.       A. Honold, T. Saku, Y. Horikoshi, and K. Kohler

            "Optical Dephasing Of Light-Hole Excitons In Gaas Single Quantum-Wells"

            Phys. Rev. B 45 (11), 6010-6014 (1992).

 

            ABSTRACT: Picosecond photon-echo experiments were performed on light-hole excitons as well as heavy-hole excitons in GaAs single quantum wells at low temperatures and low excitation intensities. The absolute values of the exciton dephasing times depend on the sample quality but the ratio of the dephasing times of both exciton types reveals a strong increase in the dephasing rate of light-hole excitons when the thickness of the quantum well is reduced below 130 angstrom. This enhanced dephasing of light-hole excitons is due to a Fano-type resonance when the lowest light-hole exciton state is energetically overlapping with electron-heavy-hole continuum states. The experimental results are in reasonable agreement with those of theoretical calculations.

 

28.       T. Horiuchi, O. Niwa, M. Morita, and H. Tabei

            "Stripping Voltammetry Of Reversible Redox Species By Self-Induced Redox Cycling"

            Anal. Chem. 64 (24), 3206-3208 (1992).

 

            ABSTRACT:

29.       R. J. Horowicz, H. Heitmann, Y. Kadota, and Y. Yamamoto

            "Gaas Microcavity Quantum-Well Laser With Enhanced Coupling Of Spontaneous Emission To The Lasing Mode"

            Appl. Phys. Lett. 61 (4), 393-395 (1992).

 

            ABSTRACT: We have observed low-threshold lasing in a GaAs single quantum-well vertical microcavity. At 4 K the quantum-well emission linewidth is reduced, and the coupling efficiency-beta of the spontaneous emission to the lasing mode is improved. The laser threshold pump power obtained for a 200 angstrom GaAs quantum well pumped by a continuous wave Ti:sapphire laser was 5 mW, corresponding to 85-mu-W absorbed power. We have compared the experimental results with the theoretical prediction, and estimated the value of beta to be 10(-2).

 

30.       N. Hussain, N. Imoto, and R. Loudon

            "Quantum-Theory Of Dynamic Interference Experiments"

            Phys. Rev. A 45 (3), 1987-1996 (1992).

 

            ABSTRACT: We calculate the first-order interference-fringe visibilities for Mach-Zehnder interferometers in which the input beam splitter has time-varying reflection and transmission coefficients. Particular attention is given to single-photon input states, and it is shown that fringes persist in appropriate conditions even for a beam splitter that alternates between complete transmission and complete reflection. The similar behavior found for input coherent and chaotic light comfirms the single-photon nature of first-order interference. The states of excitation of the internal arms of the interferometer are derived and discussed in the context of delayed-choice experiments.

 

31.       A. Imamoglu and Y. Yamamoto

            "Nonclassical Light Generation By Coulomb Blockade Of Resonant Tunneling"

            Phys. Rev. B 46 (24), 15982-15991 (1992).

 

            ABSTRACT: We show that the Coulomb blockade of resonant tunneling in semiconductor heterojunctions creates correlations between single-charge tunneling and single-photon emission events. When driven by a constant-current source, a mesoscopic p-i-i-i-n junction generates a regulated single-photon stream by single-electron-to-single-photon conversion. Under constant-voltage operation, the photon stream generated by the junction is antibunched and sub-Poissonian. The single-electron charging energy of the heterostructure has to exceed the width of the resonant subband and the characteristic energy of the thermal fluctuations for these correlations to be observable.

 

32.       A. Imamoglu, Y. Yamamoto, and P. Solomon

            "Single-Electron Thermionic-Emission Oscillations In P-N Microjunctions"

            Phys. Rev. B 46 (15), 9555-9563 (1992).

 

            ABSTRACT: We show that Coulomb-blockade-type voltage oscillations exist in constant-current driven p-n microjunctions operated at temperatures below 3 K. These oscillations occur because of the regulation of the single-electron thermionic-emission events from the n layer into the p layer. We give an expression for the average I-V characteristics of the junction in the Coulomb-blockade regime, which agrees well with the results of the computer simulations. We also predict the generation of a regulated single-photon stream from such a p-n junction.

 

33.       S. Inoue, H. Ohzu, S. Machida, and Y. Yamamoto

            "Quantum Correlation Between Longitudinal-Mode Intensities In A Multimode Squeezed Semiconductor-Laser"

            Phys. Rev. A 46 (5), 2757-2765 (1992).

 

            ABSTRACT: The intensity-noise properties of a constant-current-driven multimode semiconductor laser were studied theoretically and experimentally. It was shown that the total intensity noise of a pump-noise-suppressed multimode semiconductor laser was reduced to below the standard quantum limit even though the intensity noise of each individual mode had large excess intensity noise. This discovery stems from negative quantum correlations between longitudinal-mode intensities.

 

34.       M. Itoh, T. Saku, and S. Tarucha

            "High-Mobility Quantum Wires Fabricated By Ga Focused Ion-Beam Shallow Implantation"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 31 (12B), 4487-4491 (1992).

 

            ABSTRACT: High-mobility quantum wires are fabricated using shallow implantation of a low energy focused Ga ion beam into a modulation doped AlxGa1-xAs/GaAs heterostructure. Lowering the implant energy keeps the implanted ions away from the two-dimensional electron gas and reduces crystallographic damage. The electron mobility is 5.0 x 10(5) CM2/ V. S for the wires 10 mum long with an effective width of 0. 152 mum, which is much higher than that for previous wires. The effective wire width is independently derived from two measurements: (1) four-terminal conductance at zero-magnetic field and (2) the magnetic depopulation effect in the Shubnikov-de Haas oscillation. As the implantation dose decreases, the electron mobility increases with an effective width of more than 2. 1 -mum, while it is nearly constant for narrower wires. This suggests the existence of unintentionally implanted neutral Ga atoms and/or stray Ga ions.

 

35.       F. Izumi, K. Kinoshita, Y. Matsui, K. Yanagisawa, T. Ishigaki, T. Kamiyama, T. Yamada, and H. Asano

            "The Crystal-Structure Of The Superconducting Copper-Oxide Carbonate (Ba1-Xsrx)2cu1+Yo2+2y+Z(Co3)1-Y - Defects In Charge Reservoirs And Superconductivity"

            Physica C 196 (3-4), 227-235 (1992).

 

            ABSTRACT: The crystal structure of a new superconductor in the Ba-Sr-Cu-C-O system has been determined by neutron powder diffraction with the auxiliary use of electron diffraction and high-resolution transmission electron microscopy. This compound is a member of a solid solution with the general formula (Ba1-xSrx)2Cu1+yO2+2y+z(CO3)1-y, where x = 4/9, y = 1/9, and z = 0.10. It is tetragonal with a space group P42(1)2 or P42(1)mBAR and lattice parameters of a = 5.56405(18) angstrom and c = 7.8570(4) angstrom. It is closely related in structure to Sr2CuO2CO3, which is an end member of the solid solution: x = 1, y = 0, and z = 0. Two-dimensional CuO2 sheets and carbonate slabs, (Ba1-xSrx)2CuyO2y+z(CO3)1-y, alternate with each other along the [001] direction. As the formula of the slab shows, about 11% of C atoms are substituted by excess Cu atoms coordinated to O atoms which amount to 2y + z in the formula unit. These substitutional and interstitial defects enable hole carriers to move from the carbonate slab to the CuO2 conduction sheet.

 

36.       Y. Jimbo and A. Kawana

            "Electrical-Stimulation And Recording From Cultured Neurons Using A Planar Electrode Array"

            Bioelectrochem. Bioenerg. 29 (2), 193-204 (1992).

 

            ABSTRACT: Planar electrode arrays were fabricated using modern semiconductor technology. Mouse and chick dorsal root ganglion cells were successfully cultured on the surface of indium tin oxide electrode patterns. Contact between the neurites and the substrate electrodes was established by exploiting the surface properties of the culture substrates to guide neurite outgrowth. The guided neurites were stimulated electrically using the substrate electrodes and cell responses were recorded. intracellularly and extracellularly. Depolarization of the cell membrane as well as generation of action potentials in response to the stimulation could be observed. The results suggest that this type of planar electrode array could be a useful tool for non-invasive electrophysiological measurements.

 

37.       M. Kasu, H. Ando, H. Saito, and T. Fukui

            "Polarized Photoluminescence Of Fractional Layer Superlattices"

            Surf. Sci. 267 (1-3), 300-303 (1992).

 

            ABSTRACT: The polarization dependences of photoluminescence of (AlAs)1/2(GaAs)1/2 and (Al0.5Ga0.5As)1/2(GaAs)1/2 fractional layer superlattices were measured at room temperature. Anisotropy in light emission was observed for the first time. The photoluminescence spectra depend on its polarization. This shows that quantum carrier confinement occurs in the direction parallel to the surface, i.e., lateral quantum carrier confinement.

 

38.       M. Kasu and T. Fukui

            "Multiatomic Steps On Metalorganic Chemical Vapor Deposition-Grown Gaas Vicinal Surfaces Studied By Atomic Force Microscopy"

            Jpn. J. Appl. Phys. Part 2 - Lett. 31 (7A), L864-L866 (1992).

 

            ABSTRACT: We studied MOCVD-grown GaAs (001) vicinal surfaces by atomic force microscopy (AFM) and observed multi-atomic steps (multisteps) of several-monolayers height. The multisteps become straight as the AsH3 partial pressure increases and when the misorientation direction is [110BAR]. As growth proceeds, first, multisteps, i.e., step bunches, form and then the average distance between multisteps saturates. The multistep straightening and the multistep formation mechanisms are discussed

 

39.       G. Kido, S. Yamada, and T. Makimoto

            "Subband Structure Of 2-Dimensional Electrons At Double Silicon-Doped Atomic Layers In Gaas"

            Physica B 177 (1-4), 433-436 (1992).

 

            ABSTRACT: Longitudinal and transverse magnetoresistance experiments were carried out on GaAs with two impurity-doped planes in steady high magnetic fields up to 30 T. A large oscillation was observed in the field range higher than 10 T. The double Si-doped planes behave as a single well even for 15 nm separation of the atomic planes.

 

40.       K. Kinoshita, F. Izumi, T. Yamada, and H. Asano

            "Structure Refinements Of Superconducting And Nonsuperconducting La1.82ca1.18cu2o+/-Delta From Neutron-Diffraction Data"

            Phys. Rev. B 45 (10), 5558-5562 (1992).

 

            ABSTRACT: The crystal structures of superconducting and nonsuperconducting La1.82Ca1.18Cu2O6 +/- delta synthesized under O2 pressures of 400 and 2 atm were refined by Rietveld analysis of neutron-powder-diffraction data. These samples contained no impurities and their observed and calculated diffraction patterns were in excellent agreement. In both samples, Ca and La preferentially occupied, respectively, a 2a site in eightfold coordination and a 4e site in ninefold coordination; a slightly higher ordering was observed in the superconducting compound. An apical oxygen site was almost fully occupied. A trace of excess oxygen between two CuO2 planes was detected in the superconducting compound. Cu-O(1) and Cu-O(2) bond lengths differed a little between the two samples. Increases in cation ordering and in interstitial oxygen might be important factors determining superconductivity in this system.

 

41.       K. Kinoshita, H. Shibata, and T. Yamada

            "Crystal-Structure And Superconductivity In La1.85sr0.16ca0.99cu2o5.93+Delta"

            Phase Transit. 37 (2-3), 121-130 (1992).

 

            ABSTRACT:

42.       K. Kinoshita and T. Yamada

            "Superconductivity And Antiferromagnetism In La2-Xca1+Xcu2o6+/-Delta And La2-Xsrxcacu2o6+/-Delta"

            Phys. Rev. B 46 (14), 9116-9122 (1992).

 

            ABSTRACT: La2CaCu2O6 can be made superconducting by doping Ca or Sr in the form of La2-x(Sr,Ca)xCaCu2O6+delta and by synthesis under high O2 pressures of more than 4 atm. Superconducting properties of La2-xCa1+xCu2O6+/-delta (0.08 less-than-or-equal-to x less-than-or-equal-to 0.25) and La2-xSrxCaCu2O6+/-delta (0.07 less-than-or-equal-to x less-than-or-equal-to 0.23) as functions of composition (x) and oxygen partial pressure during synthesis (P(O2) up to 400 atm) were investigated by measuring their electrical resistivity and magnetic susceptibility. In both compounds, the superconducting transition temperature (T(c)) increased with increasing x and P(O2), and showed almost the same maximum T(c) (zero) of about 51 K at the solubility limit of Ca or Sr in La (x almost-equal-to 0. 25) with P(O2) at 400 atm, although at a lower P(O2), T(c) (zero) was higher in a Sr-doped compound than that of a Ca-doped compound. Nonsuperconducting or weakly superconducting La2-xCa1+xCu2O6+/-delta and La2-xSrxCaCu2O6+/-delta synthesized under oxygen partial pressures between 0.2 and 10 atm showed cusps in their magnetic susceptibility at around 25 K, which may result from three-dimensional (3D) antiferromagnetic ordering. The superconductivity of these compounds may appear as a result of the frustration of such 3D antiferromagnetic correlation as with other copper oxide superconductors.

 

43.       K. Kinoshita and T. Yamada

            "High-Pressure Synthesis Of Superconducting (Ba1-Xsrx)2cu1+Yo2+2y+Delta(Co3)1-Y(0.35-Less-Than-Or-Equal-To-X-Less-Th An-Or-Equal-To-0.6,Y-Approximate-To-0.1)"

            Jpn. J. Appl. Phys. Part 2 - Lett. 31 (7A), L832-L834 (1992).

 

            ABSTRACT: A new copper-oxide superconductor containing carbon (Ba1-xSrx)2Cu1+xO2+2y+delta(CO3)1-y (0.35 less-than-or-equal-to x less-than-or-equal-to 0.6, y almost-equal-to 0.1), which is structurally related to Sr2CuO2CO3, was synthesized under high oxygen pressures of more than 5 atm. The onset temperature for superconduction T(c)(onset) increased with oxygen partial pressure (P(O2)) during synthesis. Optimum P(O2) was about 50 atm and (Ba0.55Sr0.45)2Cu1.1O2.2+delta(CO3)0.9 synthesized under 50 atm O2, showed a T(c)(onset) of about 40 K and a T(c)(zero) of about 26 K.

 

44.       K. Kinoshita and T. Yamada

            "A New Copper-Oxide Superconductor Containing Carbon"

            Nature 357 (6376), 313-315 (1992).

 

            ABSTRACT: SUPERCONDUCTIVITY in the high-transition-temperature (high-T(c)) copper oxide superconductors seems to arise from layers of copper-oxygen squares, pyramids or octahedra. Recently the compound Sr2CuO2CO3 was found to contain layers of CuO6 octahedra 1 (Fig. 1), suggesting that it might be made superconducting by appropriate doping. But the presence of carbonate as an impurity is known to degrade the superconducting properties of materials such as YBa2Cu3O7-delta' and YBa2Cu4O8 (refs 2,3), much effort having been made to minimize residual carbon in these compounds by optimizing processing methods 4. It is thus of some interest to see whether Sr2CuO2CO3 can be made superconducting despite the carbonate ions incorporated in the structure. Here we report the synthesis, at 50 atm oxygen partial pressure, of superconducting (BaxSr1-x)2Cu1+yO2+2y+delta(CO3)1-y (0.4 less-than-or-equal-to x less-than-or-equal-to 0.65, y almost-equal-to 0.1), with T(c) (onset) up to approximately 40 K and zero resistance at up to approximately 26K. The crystal structure contains CuO2 sheets alternating with (BaxSr1-x)2CuyO2y+delta(CO3)1-y slabs, which serve as charge reservoir layers: substitution of approximately 10% copper for carbon in the slabs introduces holes into the CuO2 sheets, making the compound superconducting.

 

45.       N. Kobayashi and Y. Kobayashi

            "Insitu Control Of Heterointerface Quality In Movpe By Surface Photoabsorption"

            J. Cryst. Growth 124 (1-4), 525-530 (1992).

 

            ABSTRACT: Exchange reaction of Group V atoms is in situ monitored on a submonolayer scale during the MOVPE growth of pseudomorphic InAs/InP heterostructures on (001) InP substrate by the surface photo-absorption (SPA) method. When arsine was supplied onto the In surface of InP above 360-degrees-C, the substitution between As atoms of impinging AsH3 molecules and P atoms of InP surface was detected as a change in surface reflectivity. The reaction proceeded to about 0.4 monolayer exchange at 400-degrees-C, and was suppressed to less than 0.1 monolayer at 350-degrees-C. In contrast, the exchange between P atoms of impinging PH3 and As atoms of InAs surface was less than 0.1 monolayer below 400-degrees-C. To verify the formation of a metallurgically abrupt heterointerface, InAs/InP single quantum wells with 1-5 monolayers were grown at 350-degrees-C, and were characterized by transmission electron microscopy and photoluminescence. Atomic layer epitaxy was used to control precisely the InAs well thickness with an accuracy of one monolayer. A sharp and an intense quantum well photoluminescence was observed with a reasonable shift of emission energy due to the quantum size effect up to five InAs monolayers, indicating that metallurgically abrupt and atomically flat heterointerfaces were fabricated as designed.

 

46.       N. Kobayashi, Y. Kobayashi, Y. Yamauchi, and Y. Horikoshi

            "Insitu Optical Monitoring Of The Decomposition Process Of Gaseous Sources In Metal-Organic Chemical Vapor-Deposition And Atomic Layer Epitaxy"

            Appl. Surf. Sci. 60-1, 544-552 (1992).

 

            ABSTRACT: We apply surface photo-absorption (SPA) to study the heterogeneous decomposition of Group-III sources on a substrate surface during metal-organic chemical vapor deposition (MOCVD). We first show the substrate temperature (T(s)) dependence of the SPA signal at the supply of a Group-III source to a Group-V stabilized surface. The decomposition onset temperature obtained from the rising of the SPA signal, agrees well with the starting temperature of growth. Triethyl Al, Ga and In sources have lower onset temperatures than the corresponding trimethyl sources. A new Al source, trimethylamine alane, decomposes below 200-degrees-C. The region of atomic layer epitaxy (ALE) appears as a shoulder or a plateau in the neighborhood of decomposition onset. In this region, the surface is saturated by adsorption of the trimethyl source, and it is concluded that the self-limiting growth rate is caused by the intermolecular repulsion between impinging metal-organic molecules and CH3 groups metastably terminating the growth surface. SPA allows real-time control of the ALE process, because it distinguishes a metastable CH3-terminated surface from a metal one, and the growth parameters for obtaining CH3 termination are readily determined.

 

47.       N. Kobayashi and Y. Yamauchi

            "Enhancement Of Ash3 Decomposition On Highly Doped P-Gaas Surfaces"

            J. Cryst. Growth 124 (1-4), 44-48 (1992).

 

            ABSTRACT: Surface photo-absorption (SPA) was used to study the effect of semiconductor surface potential on the heterogeneous decomposition of source molecules in MOVPE. The decomposition rate of AsH3 was enhanced on the Ga surface of p-GaAs in proportion to a square root of the carrier concentration. In contrast, an enhancement on Si doped n-GaAs was negligible up to 2 X 10(18) cm-3. The decomposition activation energy was almost independent of the conduction type and of the carrier concentration. From these results, the enhancement of AsH3 decomposition on p-GaAs might be caused by an increase in the mean lifetime of AsH3 adsorption on the Ga surface of p-GaAs due to an attractive force between the dipole of the AsH3 molecule and the surface electric field. For the Group III source, a preliminary study by the scattered light method which detects the Ga droplet formation showed that the decomposition of triethylgallium was enhanced on the As surface of n+-GaAs in the kinetically controlled temperature region.

 

48.       Y. Kobayashi and N. Kobayashi

            "Insitu Interface Control Of Pseudomorphic Inas/Inp Quantum-Well Structure Growth By Surface Photoabsorption"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 31 (12A), 3988-3994 (1992).

 

            ABSTRACT: The exchange reaction of group V atoms was monitored in situ by surface photo-absorption on a submonolayer scale during metalorganic vapor phase epitaxial growth of pseudomorphic InAs/InP heterostructure on (001) InP substrates. About a 0.4-monolayer As/P exchange reaction was observed after arsine was supplied at 0.2 mumol/s onto the In surface of InP at a substrate temperature (T(s)) of 400-degrees-C. At a T(s) of 350-degrees-C, this As/P exchange reaction was suppressed to less than 0.1 monolayer. In contrast, the P/As exchange reaction was less than 0.1 monolayer below 400-degrees-C. The benefits of in situ control were shown by growing pseudomorphic InAs/InP single and multiple quantum wells with 1-12 InAs well layers at T(s)=350-degrees-C and characterizing them by cross sectional transmission electron microscopy, photoluminescence, and double crystal X-ray diffraction. Metallurgically abrupt and atomically flat heterostructures without dislocations were grown to 10 monolayer (ML) of InAs well, which corresponds to the critical layer thickness.

 

49.       Y. Kobayashi and N. Kobayashi

            "Growth-Rate Self-Limitation Mechanism In Inp Atomic Layer Epitaxy Studied By Surface Photoabsorption"

            Jpn. J. Appl. Phys. Part 2 - Lett. 31 (2A), L71-L73 (1992).

 

            ABSTRACT: The pyrolysis of trimethylindium (TMI) and phosphine (PH3) on an (001) InP surface is studied by surface photo-absorption. In the same manner as the pyrolysis of trimethylgallium on GaAs, self-limitation is observed in the change in reflectivity when TMI is supplied to a P-stabilized surface at 350-degrees-C. This result indicates that the surface is saturated by TMI adsorption to form a CH3-terminated In surface. H-2 purging after TMI adsorption increases the reflectivity further to the level of a metal surface with an In monolayer, indicating that CH3 groups desorb during purging. This paper also finds the pyrolysis of PH3 on a CH3-terminated In surface is much slower than on In metal surface. The growth rate is self-limited to less than one monolayer per cycle in InP atomic layer epitaxy because the surface is not completely transformed to a P surface during PH3 supply, as PH3 pyrolysis is slow on a CH3-terminated In surface. The growth rate approaches one monolayer per cycle when PH3 is supplied to an In metal surface produced by CH3 desorption.

 

50.       Y. Kobayashi and K. Sugii

            "Thermal-Decomposition Of Very Thin Oxide Layers On Si(111)"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 10 (4), 2308-2313 (1992).

 

            ABSTRACT: We investigate the thermal decomposition and desorption of very thin oxide layers prepared on Si (111) by oxygen adsorption as well as by chemical treatments. The oxides are examined by Auger electron spectroscopy, thermal desorption spectroscopy, and atomic force microscopy. The decomposition mechanism changes drastically at an oxide thickness of approximately 6 angstrom; the decomposition temperature depends on the formation method for oxides thicker than 6 angstrom, but the dependence disappears for oxides thinner than 6 angstrom. The former result can be qualitatively interpreted by the difference in SiO diffusivity between the oxides. The latter suggests that the decomposition rate is governed by reactions at the oxide/Si interface because the oxide layer is so thin that diffusion is not the dominant factor. The possibility of thermally removing the thin oxide layer in a dry oxygen/Si system for layer-by-layer etching or "monolayer peeling" is also discussed.

 

51.       J. T. Kucera, L. M. Rubin, K. Uwai, J. D. Perkins, J. M. Graybeal, T. P. Orlando, J. B. Vandersande, A. Roshko, and J. Moreland

            "Fabrication Of Nanometer Smooth Bi2sr2cacu2o8+ Delta Films By Reactive Cosputtering From Elemental Targets With Pure Ozone"

            Physica C 192 (1-2), 23-30 (1992).

 

            ABSTRACT: We describe the fabrication of superconducting Bi2Sr2CaCu2O8+delta thin films having root-mean-square surface roughnesses of less than 5 nm as determined by scanning tunneling microscopy. Films are deposited in-situ by RF and DC triode magnetron sputtering from elemental metallic targets in the presence of pure ozone. As deposited, these films have transition temperatures as high as 68 K and zero-field critical current densities exceeding 10(6) A/cm2 at 4.2 K. The transition temperatures can be increased to 80 K by post-deposition annealing with only a slight increase in surface roughness.

 

52.       K. Maezawa, T. Mizutani, and S. Yamada

            "Effective Mass And Ground-State Of Alas Quantum-Wells Studied By Magnetoresistance Measurements"

            J. Appl. Phys. 71 (1), 296-299 (1992).

 

            ABSTRACT: Transport properties of electrons confined in AlAs quantum wells were studied using low temperature magnetoresistance measurement. The structure used is quantum wells consisting of AlAs channel layers sandwiched by Si-doped Al0.45Ga0.55As barrier layers. This structure enables us to confine electrons in the X valleys of AlAs. The electron confinement in the AlAs quantum wells were confirmed by a mobility enhancement at low temperatures. Magnetoresistance measurements showed clear Shubnikov-de Haas oscillations for the magnetic field parallel to the growth direction. A large effective mass of (0.55 +/- 0.05) m0, which is close to square-root m(t)m(l) (m(t):transverse effective mass, m(l):longitudinal effective mass), was obtained from the temperature dependence of the oscillations. This indicates that the ground state is X(x), X(y), even though X(z) was expected to be the ground state due to its large effective mass parallel to the growth direction. This changeover of AlAs X valley states can most likely be attributed to a strain-induced energy shift caused by the small lattice mismatch between GaAs and AlAs.

 

53.       T. Makimoto and S. S. Chang

            "Carbon Modulation-Doped P-Algaas/Gaas Heterostructures Grown By Metalorganic Chemical Vapor-Deposition"

            Jpn. J. Appl. Phys. Part 2 - Lett. 31 (6B), L797-L798 (1992).

 

            ABSTRACT: Carbon atoms are used as a p-type dopant for modulation-doped p-AlGaAs/GaAs heterostructures grown by metalorganic chemical vapor deposition. Carbon impurities are effectively doped into AlGaAs layers by flow-rate modulation epitaxy, which is a modified method of metalorganic chemical vapor deposition. A mobility of 6.0 x 10(4) cm2/V.s is obtained at 13 K for a sheet carrier concentration of 4.1 x 10(11) cm-2, indicating that a high quality two-dimensional hole gas is realized by abrupt heterointerfaces and sharp carbon doping profiles.

 

54.       S. Masuyama and S. Naito

            "Deciding Whether Graph-G Has Page Number One Is In Nc"

            Inf. Process. Lett. 44 (1), 7-10 (1992).

 

            ABSTRACT: Based on a forbidden subgraph characterization of a graph to have one page, we develop a polylog time algorithm to tell if a given graph G has page number one, with polynomial number of processors, clarifying this problem to be in NC.

 

55.       N. Mitani and S. Kurihara

            "Marginal Fermi-Liquid Theory And Renormalization Effects"

            Physica C 192 (1-2), 230-236 (1992).

 

            ABSTRACT: Marginal Fermi-liquid theory proposed by Varma et al. is based on an assumption concerning the imaginary part of the polarization propagator. We investigate the consequence of this assumption paying full respect to the Ward-Takahashi identity, and find that the vertex corrections are of vital importance. We confirm the validity of the marginal Fermi-liquid picture at high energy scale, where only the lowest order logarithmic correction is important. However, our result at the low-energy region is radically different from the marginal Fermi liquid theory, in the sense that the quasi-particle mass, strength of its pole, and the jump in the momentum distribution all remain finite at the Fermi level. This means that the Varma et al. assumption does not break the Fermi-liquid picture, as far as the low-energy excitations are concerned.

 

56.       M. Mitsunaga

            "Time-Domain Optical-Data Storage By Photon-Echo"

            Opt. Quantum Electron. 24 (10), 1137-1150 (1992).

 

            ABSTRACT: Principles and applications of time-domain optical data storage using stimulated photon echo are briefly reviewed. Special emphasis is laid upon the comparison of this memory with holography; both memories use the interference between two optical waves. Some new experimental developments are introduced using samples of europium-ion-doped crystals, one of the most promising candidates in time-domain data storage. Some other topics, such as ultrafast data storage, time-domain data processing, and time- and spatial-image storage using photon echo, are also discussed.

 

57.       M. Mitsunaga, T. Takagahara, R. Yano, and N. Uesugi

            "Excitation-Induced Frequency-Shift Probed By Stimulated Photon-Echoes"

            Phys. Rev. Lett. 68 (21), 3216-3219 (1992).

 

            ABSTRACT: A stimulated photon-echo study has verified the instantaneous shift (less-than-or-equal-to 1 MHz) and subsequent restoration (approximately 2 ms) of the transition frequency of an impurity ion in a solid when its neighboring ions are exposed to pulsed optical excitation. Experiments were conducted by monitoring the echo intensity for the F-7(0)-5D0 transition of Eu ions in one site of Y2SiO5, while exciting the other site. A photon-echo theory taking account of the stochastic frequency recovery is developed to explain the observations.

 

58.       M. Mitsunaga, R. Yano, and N. Uesugi

            "Stimulated-Photon-Echo Spectroscopy.2. Echo Modulation In Pr3+ Yalo3"

            Phys. Rev. B 45 (22), 12760-12768 (1992).

 

            ABSTRACT: Stimulated-photon-echo measurements as a function of both the first-to-second (tau) and the second-to-third (T) pulse separations were conducted to study the echo-modulation behavior for the H-3(4)-D-1(2) transition of a cryogenic Pr3+:YAlO3 sample. When T is shorter than the excited-state lifetime T1, deep echo modulations along both the tau and T axes are observed, the frequencies of which correspond to the excited-state sublevel splittings. When T exceeds T1, the modulation is still observed, although only along the tau-axis. A density-matrix theory is developed in a perturbative manner to explain these coherent dynamical properties. The numerically simulated three-dimensional plots of the echo intensity versus tau and T are presented, predicting quite satisfactorily the seemingly complicated experimental modulation patterns.

 

59.       F. Mokhtarian and A. K. Mackworth

            "A Theory Of Multiscale, Curvature-Based Shape Representation For Planar Curves"

            IEEE Trans. Pattern Anal. Mach. Intell. 14 (8), 789-805 (1992).

 

            ABSTRACT: This paper presents a multiscale, curvature-based shape representation technique for planar curves that satisfies several criteria that are considered necessary for general-purpose shape representation methods. As a result, the representation is suitable for tasks that call for recognition of a noisy curve of arbitrary shape at an arbitrary scale or orientation. The method rests on the concept of describing a curve at varying levels of detail using features that are invariant with respect to transformations that do not change the shape of the curve. Three different ways of computing the representation are described in this paper. These three methods result in three different representations: the curvature scale space image, the renormalized curvature scale space image, and the resampled curvature scale space image. The process of describing a curve at increasing levels of abstraction is referred to as the evolution or arc length evolution of that curve. Several evolution and arc length evolution properties of planar curves are described in this paper. Some of these results show that evolution and arc length evolution do not change the physical interpretation of planar curves as object boundaries, and some characterize possible behaviors of planar curves during evolution and arc length evolution. Others impose constraints on the location of a planar curve as it evolves. Together, these results provide a sound theoretical foundation for the representation methods introduced in this paper.

 

60.       M. Morita, T. Horiuchi, and H. Tabei

            "Differential Pulse Voltammetry Of Reversible Redox Species At Interdigitated Array Electrodes"

            J. Electroanal. Chem. 322 (1-2), 191-201 (1992).

 

            ABSTRACT: Differential pulse (DP) voltammetry of reversible redox species has been measured with interdigitated array (IDA) electrodes in single and dual potentiostated modes. The concentration profile near the electrode was renewed rapidly because of non-planar diffusion toward the electrode. Therefore, no depletion effect was observed in either mode when the waiting time was 0.4 or 5 s. The pulse electrolysis time and the applied pulse potential dependence of the peak currents in the single mode follow conventional DP voltammetry with a macro electrode. However, constant peak currents were observed in the dual mode which depended on the applied pulse potential and the average diffusion distance calculated from the IDA electrode configuration. The current in a DP voltammogram with IDA electrodes in the dual mode can be expressed as (DELTA-i)max = i(lim)[(1 - sigma)/(1 + sigma)] where i(lim) is the limiting current in the cyclic voltammogram with the IDA in the dual mode. The sensitivity for ferrocene derivatives was improved up to 2 nmol/dm3 as a result of the high collection efficiency and redox cycling.

 

61.       H. Murase

            "Surface Shape Reconstruction Of A Nonrigid Transparent Object Using Refraction And Motion"

            IEEE Trans. Pattern Anal. Mach. Intell. 14 (10), 1045-1052 (1992).

 

            ABSTRACT: The appearance of a pattern behind a transparent, moving object is distorted by refraction at the moving object's surface. This paper describes an algorithm for reconstructing the surface shape of a nonrigid transparent object, such as water, from the apparent motion of the observed pattern. This algorithm is based on the optical and statistical analysis of the distortions. It consists of the following parts: 1) extraction of optical flow, 2) averaging of each point trajectory obtained from the optical flow sequence, 3) calculation of the surface normal using optical characteristics, and 4) reconstruction of the surface. The algorithm is applied to both synthetic and real images to demonstrate its performance.

 

62.       K. Nakamura and H. Nakano

            "Faraday-Rotation In Cd1-Xmnxte/Cd1-Yznyte Superlattice"

            J. Phys. Soc. Jpn. 61 (4), 1390-1398 (1992).

 

            ABSTRACT: The present paper is concerned with an experimental study of Faraday rotation in a Cd0.89Mn0.11Te/Cd0.61Zn0.39Te superlattice at 300 K and 4.2 K. As the width of Cd0.89Mn0.11Te well decreases, a lying-S shaped dispersion of the Faraday rotation spectrum, which is consistent with a predominant exciton transition of \ 3/2, +/- 3/2 > to \ 1/2, +/- 1/2 >, shifts toward a higher photon energy, and the peak value of the dispersion spectrum becomes larger than that for the Cd0.89Mn0.11Te thin film. In the superlattice systems, we also observed a Faraday rotation spectrum consistent with the exciton transition of \ 3/2, +/- 1/2 > to \ 1/2, +/- 1/2 > at a higher photon energy. The shift of the energy-band gap due to the lattice-mismatch is calculated for this system on the basis of the model of free standing strained superlattice. The positions of calculated energy in the dispersion spectrum are in good agreement with experimental results.

 

63.       J. Nakata, M. Taniguchi, and K. Takahei

            "Direct Evidence Of Er Atoms Occupying An Interstitial Site In Metalorganic Chemical Vapor Deposition-Grown Gaaser"

            Appl. Phys. Lett. 61 (22), 2665-2667 (1992).

 

           ABSTRACT: Er doped GaAs grown by metalorganic chemical vapor deposition is studied by the Rutherford backscattering channeling method. We directly confirmed, for the first time, that Er ions occupy a somewhat displaced tetrahedral interstitial site, rather than a substitutional site, in the GaAs host. This is concluded from the observation of a remarkable peak of the doped Er ions caused by the flux peaking effect in the [110] channeling direction. Also leading to this conclusion is the fact that the ratios of the [111] and [100] channeling yields to the random yields for Er ions were larger than those for the GaAs host. Moreover, we observe peak shifts towards the higher energy region in the [110] spectra compared to the random spectra. This is due to the lower stopping power of He ions in the GaAs host in the channeling direction than in the random direction. We deduce the strikingly small stopping power ratio of the [110] to the random incidence is also discussed.

 

64.       S. Nakata

            "Observation Of Tunneling Phenomena And The Charging Effect Through Small Constricted Regions In Semiconductors Fabricated With A Focused Ion-Beam At 4.2-K"

            Phys. Rev. B 46 (20), 13326-13330 (1992).

 

            ABSTRACT: Small tunnel barrier were formed on AlxGa1-xAs/GaAs by focused-ion-beam implantation. The samples were then measured with dc current at 4.2 K, and the I-V curves revealed two distinct regions depending on applied bias: a tunneling region at small bias voltage and a region where thermal current over the barrier is dominant at large bias voltage. A dip in the dI/dV curve was observed in the tunneling region in the source-drain voltage (V(SD)) range from - 5 to 5 mV. In a different sample, periodic and reproducible staircaselike steps with a periodicity DELTAV(SD) of 35 mV were observed. This phenomenon is related to he Coulomb staircase, which occurs when the capacitance of a quantum dot is very small.

 

65.       S. Nishida and T. Sato

            "Positive Motion After-Effect Induced By Bandpass-Filtered Random-Dot Kinematograms"

            Vision Res. 32 (9), 1635-1646 (1992).

 

            ABSTRACT: Using spatially filtered random-dot kinematograms (RDK) with a 1 octave bandwidth, the duration and direction of motion aftereffect (MAE) were measured while varying step displacement, and the results were compared to those for motion direction discrimination. We found that MAE and motion discrimination show quite different dependencies on displacement. At displacements around 0.5 cycles of the lowest frequency, while motion discrimination was still almost perfect, normal MAE vanished and MAE in the same direction as that of the adapting stimuli, which we name "positive MAE", was observed. Similar results were obtained for both 1- and 2-dimensional filtered patterns. A theoretical examination based on the Fourier components of the stimuli showed that the displacement dependency of MAE is predictable in terms of adaptation of first-order detectors, but that of motion discrimination is not. The present results indicate that direction perception and MAE for bandpass RDKs are mediated at least partially by separate mechanisms, and that direction perception at larger displacements is mediated by the second-order mechanism which detects movement of contrast modulation in the image.

 

66.       J. Nitta, T. Akazaki, H. Takayanagi, and K. Arai

            "Transport-Properties In An Inas-Inserted-Channel In0.52al0.48as/In0.53ga0.47as Heterostructure Coupled Superconducting Junction"

            Phys. Rev. B 46 (21), 14286-14289 (1992).

 

            ABSTRACT: Supercurrent is observed in a superconductor-semiconductor-superconductor (S-Sm-S) junction using a two-dimensional-electron-gas system in an InAs-inserted-channel In0.52Al0.48As/In0.53Ga0.47As heterostructure. The temperature dependence of the supercurrent cannot be explained by a simple exponential expression, but is here explained in terms of the clean-limit theory, taking account of the higher-order effect of the coherence length. The differential resistance of the junction shows clear subharmonic energy-gap structures due to multiple Andreev reflection since the phase coherence is maintained during the Andreev-reflection process. The Cooper pair transport explained by the clean-limit theory is attributed to the fact that the mean free path is longer than the coherence length and the length between the superconducting electrodes.

 

67.       K. Nozawa and Y. Horikoshi

            "Low Threading Dislocation Density Gaas On Si(100) With Ingaas/Gaas Strained-Layer Superlattice Grown By Migration-Enhanced Epitaxy"

            J. Electron. Mater. 21 (6), 641-645 (1992).

 

            ABSTRACT: This paper reports a promising approach for reducing the density of threading dislocations in GaAs on Si. InxGa1-xAs/GaAs strained-layer superlattices (SLSs) grown by migration-enhanced epitaxy at 300-degrees-C on GaAs/Si acted as barriers to threading dislocations. Unlike conventional high-temperature-grown SLSs, the low-temperature-grown SLSs were hardly relaxed by the formation of misfit dislocations at GaAs/SLS interfaces, and this allowed them to accumulate considerable strain. New threading dislocation generation due to the misfit dislocation was also suppressed. These factors caused effective bending of threading dislocations and significantly reduced the dislocation density. For the samples that had an SLS with x = 0.3, the average etch-pit density was 7 X 10(4) cm-2, which is comparable to that of GaAs substrates.

 

68.       M. Ogawa

            "Chew Theorem Revisited - Uniquely Normalizing Property Of Nonlinear Term Rewriting-Systems"

            Lect. Notes Comput. Sci. 650, 309-318 (1992).

 

            ABSTRACT: This paper gives a purely syntactical proof, based on proof normalization techniques, of an extension of Chew's theorem. The main theorem is that a weakly compatible TRS is uniquely normalizing. Roughly speaking, the weakly compatible condition allows possibly nonlinear TRSs to have nonroot overlapping rules that return the same results. This result implies the consistency of CL-pc which is an extension of the combinatory logic CL with parallel-if rules.

 

69.       T. Ogawa, A. Furusaki, and N. Nagaosa

            "Fermi-Edge Singularity In One-Dimensional Systems"

            Phys. Rev. Lett. 68 (24), 3638-3641 (1992).

 

            ABSTRACT: The Fermi-edge singularity in optical spectra is studied theoretically using the Tomonaga-Luttinger model for one-dimensional (1D) systems. Its critical exponent is obtained analytically for an arbitrary mass of a valence hole taking into account the electronic correlation. The exponent is found to be independent of the hole dynamics in 1D, which is in striking contrast to the 2D and 3D cases. Weak repulsive interaction among the conduction electrons sharpens the power-law peak in the edge spectrum.

 

70.       T. Ogawa and T. Takagahara

            "Excitonic Absorption-Spectra And Sommerfeld Factors Of One-Dimensional Systems"

            Surf. Sci. 263 (1-3), 506-511 (1992).

 

            ABSTRACT: We investigate theoretically optical absorption spectra near a band edge for one-dimensional (1D) semiconductors with a direct band gap, taking 1D Wannier-type exciton effects into account. The Sommerfeld factor, which is the absorption intensity ratio of the continuum exciton to the free electron-hole pair above the band edge, is found to be smaller than unity for an allowed transition in striking contrast to the three- and two-dimensional cases. This peculiar feature is interpreted in terms of the anomalously strong concentration of the oscillator strength on the lowest discrete exciton state.

 

71.       T. Ohno, K. Shiraishi, and T. Ogawa

            "Intrinsic Origin Of Visible-Light Emission From Silicon Quantum Wires - Electronic-Structure And Geometrically Restricted Exciton"

            Phys. Rev. Lett. 69 (16), 2400-2403 (1992).

 

            ABSTRACT: We theoretically investigate excitonic effects on the optical properties of silicon quantum wires, based on ab initio electronic structure calculations. The Si wires have a direct, allowed band gap in the visible energy range and exhibit a strong optical anisotropy. Taking into account the electron-hole Coulomb interaction, the geometrical restriction of excitons dramatically enhances the oscillator strength of the optical transitions. Comparisons with recent experimental results are also made.

 

72.       M. Okada

            "An Efficient One-Pass Search Algorithm For Parsing Spoken Language"

            IEICE Trans. Fundam. Electron. Commun. Comput. Sci. E75A (7), 944-953 (1992).

 

            ABSTRACT: Spoken language systems such as speech-to-speech dialog translation systems have been gaining more attention in recent years. These systems require full integration of speech recognition and natural language understanding. This paper presents an efficient parsing algorithm that integrates the search problems of speech processing and language processing. The parsing algorithm we propose here is regarded as an extension of the finite-state-network directed, one-pass search algorithm to one directed by a context-free grammar with retention of the time-synchronous procedure. The extended search algorithm is used to find approximately globally optimal sentence hypotheses; it does not have overhead which exists in, for example, hierarchical systems based on the lattice parsing approach. The computational complexity of this search algorithm is proportional to the length of the input speech. As the search process in the speech recognition can directly take account of the predictive information in the sentence parsing, this framework can be extended to spoken language systems which deal with dynamically varying constraints in dialogue situations.

 

73.       Y. Okada and M. Hayashi

            "Graph Rewriting-Systems And Their Application To Network Reliability-Analysis"

            Lect. Notes Comput. Sci. 570, 36-47 (1992).

 

            ABSTRACT: We propose a new kind of Graph Rewriting Systems (GRS) that provide a theoretical foundation for using the reduction methods to analyze network reliability, and give the critical pair lemma in this paper.

 

74.       N. Osaka, K. Kakehi, S. Iai, and N. Kitawaki

            "A Model For Evaluating Talker Echo And Sidetone In A Telephone Transmission Network"

            IEEE Trans. Commun. 40 (11), 1684-1692 (1992).

 

            ABSTRACT: We are studying an objective evaluation model called OPINE (overall performance index model for network evaluation) for telephone transmission quality. The model estimates an MOS (mean opinion score) by summing psychological values on independent psychological factors, given the physical values of fundamental listening factors such as loss and noise. For the model to incorporate new talking factors such as talker echo and sidestone, evaluation characteristics are studied when both listening and talking factors are present in a telephone transmission system. This paper focuses on the interaction of the listening and talking factors and shows experimentally that these talking factors are independent of fundamental listening factors. From these results, an extended OPINE is proposed by establishing new psychological factors: talker echo and sidestone. The estimated MOS for composite conditions of listening and talking factors agrees well within the confidence interval of subjective MOS deviation. In addition, the results of comparison with another model are shown.

 

75.       K. Otsuka

            "Highly Sensitive Measurement Of Doppler-Shift With A Microchip Solid-State Laser"

            Jpn. J. Appl. Phys. Part 2 - Lett. 31 (11A), L1546-L1548 (1992).

 

            ABSTRACT: Intensity modulation of a LiNdP4O12 microchip solid-state laser by reflected scattered light from a moving object is investigated experimentally and numerically. Ultra-high sensitivity detection of Doppler-shift and application to a laser velocity meter are demonstrated.

 

76.       K. Otsuka and J. L. Chern

            "Dynamic Spatial-Pattern Memory In Globally Coupled Lasers"

            Phys. Rev. A 45 (11), 8288-8291 (1992).

 

            ABSTRACT: The chaotic dynamics found in globally coupled modulated laser systems have been switched into stable orbits, including antiphase periodic states and clustered states, by an injection-seeding method. Direct assignment to desired factorial periodic orbits has been demonstrated. Self-induced switching among destabilized clustered states (chaotic itinerancy) in the transition process from clustered states to global chaos has also been found.

 

77.       K. Otsuka and J. L. Chern

            "Synchronization, Attractor Fission, And Attractor Fusion In A Globally Coupled Laser System"

            Phys. Rev. A 45 (7), 5052-5055 (1992).

 

            ABSTRACT: A globally coupled class-B laser array with incoherent feedback is proposed for exploring the complex dynamics of dynamical systems with the highest connectivity. This feedback shows a fundamental characteristic, information lag, and results in the general features of synchronization, attractor fission, and attractor fusion processes. The common characteristics shared by different clusters in the segregation process are found. The effect of multiple different time delays on synchronization is also investigated.

 

78.       K. Otsuka, M. Georgiou, and P. Mandel

            "Intensity Fluctuations In Multimode Lasers With Spatial Hole Burning"

            Jpn. J. Appl. Phys. Part 2 - Lett. 31 (9A), L1250-L1252 (1992).

 

            ABSTRACT: The intensity fluctuations in multimode lasers with spatial hole burning are investigated. We give experimental evidence for a self-organized collective behavior resulting from the cross saturation dynamics of spatially hole-burned lasers, in which each mode is characterized by N relaxation oscillation frequencies omega(l) (l = 1, 2, 3., N; N: number of oscillating modes), while the total output exhibits a unique relaxation oscillation at the highest frequency in omega(l) which coincides with that in a single mode laser.

 

79.       K. Otsuka, P. Mandel, S. Bielawski, D. Derozier, and P. Glorieux

            "Alternate Time Scale In Multimode Lasers"

            Phys. Rev. A 46 (3), 1692-1695 (1992).

 

            ABSTRACT: We analyze the intensity fluctuation of multimode lasers by extending the linear-response theory of McCumber for single-mode lasers. In the two-mode case, we prove analytically that the rate equations allow for an additional dynamical oscillation frequency associated with the antiphase motion. This explains the self-organized collective behavior of two-mode lasers, i.e., that the total output behaves just like a single-mode laser. The linear stability predicts the scaling law for this time scale, which results quite generally through cross-saturation dynamics of population inversion. Experimental results in two different laser systems confirm these predictions.

 

80.       J. R. Phillips, K. Tsubaki, T. Saku, and S. Tarucha

            "Low-Frequency Noise In Very High Mobility Modulation-Doped Structures"

            Appl. Phys. Lett. 61 (24), 2926-2928 (1992).

 

            ABSTRACT: We report here on the observation of low-frequency (1-100 Hz) noise characteristics as a function of current in very high mobility four-terminal structures at 4.2 K. At low currents, the noise levels are too low to be observed with our measurement system. When the mobility is decreased by a change in gate voltage, or when the injected current is increased, noise levels increased. At currents where excess noise is observable, the channel current-voltage characteristics are nonlinear and the noise current dependence is superquadratic. The steep current-dependence results from the degradation of mobility due to electron heating, with the subsequent rapid noise increase due to optical phonon scattering.

 

81.       T. S. Rao, Y. Horikoshi, C. Jagadish, R. G. Elliman, and J. S. Williams

            "Characterization Of Gaas/Si/Gaas Heterostructures"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 31 (10), 3282-3286 (1992).

 

            ABSTRACT: GaAs/Si(n)/GaAs, n = 1 to 3 mono-layers (ML) were grown on GaAs (100) substrates using molecular beam epitaxy. Double crystal X-ray diffraction rocking curve and Rutherford backscattering/chanelling studies indicated that 1 ML of Si grows coherently and psuedomorphicatly on GaAs and 2 and 3 ML Si exhibit increasing defect nature and are probably relaxed. Raman scattering measurements of the cap GaAs layer showed an increase in intensity of forbidden transverse optical (TO) phonon peak with increasing underlying Si layer thickness. Cross-sectional transmission electron microscopy studies revealed that for 1 ML Si, the Si-GaAs interface and the Si layer are defect free. However, for increasing thickness of Si to n = 2 and 3 ML, defect density increased at the Si-GaAs cap layer interface.

 

82.       T. S. Rao, K. Nozawa, and Y. Horikoshi

            "Growth Of Gaas On Hydrogen-Fluoride Treated Si (100) Surfaces Using Migration-Enhanced Epitaxy"

            Appl. Phys. Lett. 60 (13), 1606-1608 (1992).

 

            ABSTRACT: Heteroepitaxial growth of GaAs has been successfully achieved for the first time using migration-enhanced epitaxy (300-degrees-C) on HF treated Si substrates which have been subjected to an initial in situ pre-heat treatment in the range of 350-620-degrees-C and without the customary high-temperature Si oxide desorption step. High quality GaAs on Si exhibiting double-crystal x-ray rocking curve full-width at half-maximum value of 280 arcsec was obtained by using two-step growth technique MEE(300-degrees-C)/MBE (580-degrees-C). Secondary-ion mass spectrometry studies indicated 0.05 (monolayer) ML of oxygen at the interface of GaAs and HF treated Si substrate. The photoluminescene spectra at 10 K for GaAs grown on HF treated Si substrates was dominated by sharp excitonic related peaks and no carbon acceptor related emission could be detected.

 

83.       H. P. C. Robinson, K. Torimitsu, Y. Kuroda, and A. Kawana

            "Characterization Of Spontaneous Synchronized Calcium Transients In Cultured Networks Of Cerebral Cortical-Neurons"

            Faseb J. 6 (1), A511-A511 (1992).

 

            ABSTRACT:

84.       N. Sarukura and Y. Ishida

            "Ultrashort Pulse Generation From A Passively Mode-Locked Ti-Sapphire Laser Based System"

            IEEE J. Quantum Electron. 28 (10), 2134-2141 (1992).

 

            ABSTRACT: The detailed characteristics of a passively mode-locked Ti:sapphire laser using saturable absorbers are described. This laser can stably generate nearly transform-limited sub-100-fs pulses around 780 nm. Combining with this oscillator and a double-pass Ti:sapphire amplifier pumped by a CW Q-switched YAG laser (3 kHz) enables fiber-grating pulse compression down to 14 fs.

 

85.       N. Sarukura and Y. Ishida

            "Pulse Evolution Dynamics Of A Femtosecond Passively Mode-Locked Ti-Sapphire Laser"

            Opt. Lett. 17 (1), 61-63 (1992).

 

            ABSTRACT: The pulse-formation process in a femtosecond passively mode-locked Ti:sapphire laser with a saturable absorber is investigated. The time to reach the steady state is approximately 200-mu-s. The formation time dependence on the dye concentration and the coincidence of the steady-state pulse width with the self-mode-locked state without a saturable absorber indicate that the function of the saturable absorber is mainly to induce the initial modulation and to shorten the pulse-formation time.

 

86.       H. Sato, M. Naito, T. Arima, and Y. Tokura

            "La2-Xsrxcuo4(110) Thin-Films Epitaxially Grown Along The Cuo2 Plane On Pr2cuo4 Single-Crystals"

            Appl. Phys. Lett. 61 (20), 2470-2472 (1992).

 

            ABSTRACT: The epitaxial growth of superconducting copper oxide films on nondoped insulating copper oxide single crystals produced high-quality epitaxy perpendicular to the c axis, namely along the CuO2 plane. The (110) oriented La1.84Sr0.16CuO4 (LSCO) thin films with T(c) = 21 K were successfully grown on (110) Pr2CuO4 single-crystal substrates using 90-degrees off-axis sputtering. The x-ray diffraction and the anisotropic resistivity indicate perfect in-plane epitaxy. Scanning electron microscopy (SEM) shows fairly smooth surface of the (110) LSCO film.

 

87.       M. Sato and Y. Horikoshi

            "Effect Of Indium Replacement By Gallium On Inas/Gaas Quantized Levels"

            Surf. Sci. 267 (1-3), 195-198 (1992).

 

            ABSTRACT: Quantized levels of InAs/GaAs thin layer structures are calculated using a modified finite square well model, which takes into account In-Ga replacement during growth. Comparison between the calculated results and experimental band gaps indicates that In-Ga replacement rarely occurs in flow-rate modulation epitaxy and that, in contrast, about 90% of the surface In is replaced by Ga in molecular beam epitaxy. The effect of the replacement on the modulation of GaAs/AlGaAs quantized levels by InAs layer insertion is also demonstrated.

 

88.       S. C. Shi, S. Ando, and T. Fukui

            "Fabrication Of High-Density Ultrafine Gaas Quantum Wire Array Structures Using Selective Metalorganic Chemical Vapor-Deposition"

            Surf. Sci. 267 (1-3), 214-217 (1992).

 

            ABSTRACT: High density GaAs quantum wire array structures have been successfully fabricated on an extremely short-period pattern. The quantum wire arrays were formed on the sidewall gratings of a rectangular AlGaAs/GaAs multilayer structure, selectively grown on a SiO2 masking (111)B substrate. The quantum wires with the dimension of 25 x 35 nm2 had a period as small as 95 nm. The fabrication process involved only selective metalorganic chemical vapor deposition and a selective etching technique. No nanolithography patterning techniques were used. The detailed fabrication process is presented.

 

89.       N. Shigekawa and E. Yamaguchi

            "Effects Of Disorder On Electronic Conduction Properties At Subsidiary Energy Minima In Ternary Ingaas Alloys"

            Semicond. Sci. Technol. 7 (3B), B369-B371 (1992).

 

            ABSTRACT: The effects of disorder on the electronic conduction properties at subsidiary energy minima (upper valleys) of In0.53Ga0.47As alloys are evaluated using a novel Monte Carlo supercell approach with both the band-length and bond-angle fluctuations considered. It is found that the width of the spectral function obtained in the present approach is much larger than that obtained using the coherent-potential approximation (CPA). This result indicates that the bond-length and the bond-angle fluctuations-which are not sufficiently considered in the CPA framework-induce strong effects on the electronic properties of the upper valleys.

 

90.       A. Shimizu, T. Ogawa, and H. Sakaki

            "2-Photon Absorption-Spectra Of Quasi-Low-Dimensional Exciton Systems"

            Phys. Rev. B 45 (19), 11338-11341 (1992).

 

           ABSTRACT: We present a unified theory for two-photon absorption (TPA) spectra of Wannier excitons in a low-dimensional semiconductor of an arbitrary dimension d = 0, 1, 2, and 3. It is found that the spectra strongly reflect the anisotropies of both the band structure and the quasi-d-dimensional exciton envelope functions. Therefore the low dimensionality can be sensitively detected by the TPA spectroscopy. This is in striking contrast to the one-photon absorption spectra, anisotropies of which cannot be taken as evidence of quantum confinements.

 

91.       A. Shimizu, T. Ogawa, and H. Sakaki

            "2-Photon Absorption-Spectra Of Low-Dimensional Semiconductors"

            Surf. Sci. 263 (1-3), 512-517 (1992).

 

            ABSTRACT: We present a unified theory of two-photon absorption spectra of low-dimensional semiconductors of an arbitrary dimension d = 0, 1, 2, 3. Widths of confining potentials are assumed to be smaller than the exciton Bohr radius, and the quasi-d-dimensional excitons play crucial roles in determining the spectra. When d = 1 and 2, the spectra strongly depend on the polarization direction of the incident light beam. This anisotropy comes from both anisotropies of the exciton envelope functions and anisotropic band structure. This is in striking contrast to one-photon absorption.

 

92.       A. Shimizu and M. Ueda

            "Effects Of Dephasing And Dissipation On Quantum Noise In Conductors"

            Phys. Rev. Lett. 69 (9), 1403-1406 (1992).

 

            ABSTRACT: We consider the nonequilibrium quantum noise of electrical current in one-dimensional conductors, and clarify the mechanism that distinguishes macroscopic conductors from mesoscopic conductors. The noise does not become of the macroscopic type even when a strong dephasing is introduced. Macroscopic noise is obtained only when the energy of the total electron system is maximally dissipated when each electron traverses the conductor. Energy transfer from the electron system to other systems is therefore essential for noise suppression and for the noise to be macroscopic.

 

93.       A. Shimizu, M. Ueda, and H. Sakaki

            "Quantum Noises In Mesoscopic Conductors - Origins And Suppression"

            Inst. Phys. Conf. Ser. (127), 29-32 (1992).

 

            ABSTRACT: It is pointed out that the excess noise of mesoscopic conductors found by Lesovik is the usual granularity noise, which is a general noise of quantum mechanics. It is also shown that neither the dephasing nor the electron-electron inelastic scattering is sufficient to suppress the excess noise. The excess noise is suppressed and the noise characteristics becomes those of macroscopic conductors only when the transit time of an electron across the conductor exceeds the energy relaxation time due to the electron-phonon scatterings.

 

94.       Y. Shinoda, N. Shimizu, H. Hibino, T. Nishioka, C. Heimlich, Y. Kobayashi, S. Ishizawa, K. Sugii, and M. Seki

            "Surface Structural-Changes During The Initial Growth Of Ge On Si(111)7 X 7"

            Appl. Surf. Sci. 60-1, 112-119 (1992).

 

            ABSTRACT: Reconstruction and the surface morphology of Ge layers on Si(111)7 x 7 during the initial growth stages were studied by reflection high-energy electron diffraction (RHEED) and transmission electron microscopy (TEM). The behavior of the Ge layer subjected to a thermal process was clarified by solid-phase epitaxy (SPE). By systematically varying the deposition thickness and temperature, the growth mode was confirmed to be the Stranski-Krastanov mode and the three-dimensional islands were found to form at 6.5 angstrom (equivalent to 4 ML). The 5 x 5 reconstructed structure was found to be characteristic of the low coverage (below the critical thickness) and high-temperature annealing (450-650-degrees-C). The double-step SPE, i.e., 5 angstrom Ge deposition (below the critical thickness) followed by 2 angstrom Ge deposition (over the critical thickness), revealed an apparent increase in the critical thickness. The results show that the 5 x 5 reconstructed structure is derived from intermixing Ge into the Si substrate.

 

95.       H. Shinojima, J. Yumoto, and N. Uesugi

            "Size Dependence Of Optical Nonlinearity Of Cdsse Microcrystallites Doped In Glass"

            Appl. Phys. Lett. 60 (3), 298-300 (1992).

 

            ABSTRACT: This paper investigates the size dependence of the effective nonlinear cross section sigma(eff) and the carrier recombination time on the size of CdS0.12Se0.88 microcrystallites with average radii of 10, 30, 50, and 100 angstrom by degenerate four-wave mixing (DFWM) experiments. The decay curves of the DFWM signal as a function of the probe delay time have fast and slow components. As the microcrystallite size decreases, the fast component becomes dominant and a carrier recombination time of 2 ps was observed in the 10-angstrom microcrystallites. The diffraction efficiency of DFWM is almost the same for all microcrystallites, that is, sigma(eff) has a weak size dependence. Smaller microcrystallites show smaller magnitudes of the third-order nonlinear susceptibility \chi(3)\, which is calculated from the measured effective nonlinear cross section and the carrier recombination time.

 

96.       K. Shiraishi

            "1st-Principles Calculation Of The Migration Energy Of A Ga Adatom On An As-Stabilized Gaas(001) Surface"

            Appl. Surf. Sci. 60-1, 210-214 (1992).

 

            ABSTRACT: We investigated the microscopic processes of a Ga adatom migration on an As-stabilized GaAs(001) surface. The adiabatic potential surface of a Ga adatom migration was calculated by the first-principles pseudopotential method on the basis of local density functional formalism. We found that the most stable Ga adsorption site is on the missing As dimer row and that the most favorable migration pass is in the [110BAR] direction through the missing As dimer row. The calculated activation barriers of a Ga adatom migration were 0.2 and 0.6 eV in the [110BAR] and [110] directions, respectively.

 

97.       K. Shiraishi

            "Ga Adatom Diffusion On An As-Stabilized Gaas(001) Surface Via Missing As Dimer Rows - 1st-Principles Calculation"

            Appl. Phys. Lett. 60 (11), 1363-1365 (1992).

 

            ABSTRACT: We have investigated the microscopic processes of Ga adatom diffusions on an As-stabilized GaAs(001) surface by the first-principles pseudopotential method. The results show that Ga adatoms diffuse on the surface by passing through the missing As dimer rows. Comparison with the results of scanning tunneling microscopy (STM) experiments during molecular beam epitaxy (MBE) growth suggests that low As pressure increases the surface Ga adatom diffusion by a formation of the continuous Ga adatom diffusion path. This is consistent with the fact that low temperature growth is possible by migration enhanced epitaxy (MEE), in which As and Ga sources are supplied alternately.

 

98.       M. P. Stopa

            "Self-Consistent Electronic-Structure And Optical Selection-Rules For Tetrahedral Quantum Dots"

            Surf. Sci. 267 (1-3), 286-290 (1992).

 

            ABSTRACT: Recently, Fukui et al. (22nd conference on solid state devices and materials, 1990, Japan) have employed a controlled faceting technique in metal organic chemical vapor deposition (MOCVD) crystal growth to construct tetrahedral quantum dots without resorting to ion-implantation or chemical-etching techniques. We investigate the electronic structure of these dots, in the two-dimensional flat triangular approximation, with Hartree and exchange-correlation interactions between electrons taken into account. We compute the self-consistent electronic structure of a triangular dot in a density functional formalism, taking into account finite barrier height and treating exchange and correlation in the local density approximation. We present the results of eigenvalues and density profiles as a function of charge number N, dot size, and (perpendicular) magnetic field strength. We show that the three-fold symmetry of the dot implies a form of the Bloch theorem that separates the eigenfunctions into 'zones'. This allows us further to derive selection rules for long-wavelength electromagnetic waves polarized arbitrarily within the plane of the dot. These selection rules are independent of self-consistent effects.

 

99.       M. P. Stopa

            "Charging Energy And Collective Response Of A Quantum Dot Resonant Tunneling Device"

            Surf. Sci. 263 (1-3), 433-437 (1992).

 

            ABSTRACT: Recent self-consistent electronic structure calculations and linear response calculations of the current have sought to clarify the role of Coulomb charging of a flat quantum dot connected via tunneling barriers to a two-dimensional electron gas collector and emitter. In particular, resonant tunneling through such a structure, which is observed to be periodic in a gate voltage applied to the dot, is currently explained in terms of resonant suppression of the Coulomb blockade by the gate. Nonetheless questions remain regarding the off resonance activation energy and the possible role of collective excitations of the dot. We calculate the self-consistent electronic structure of a two-dimensional quantum dot connected via point-contact tunneling barriers to two wide 2DEG regions, in the Hartree approximation. We include the effect of finite source-drain voltage and side-gate voltages. We compute the charging energy for a single electron entering the dot and discuss the dot capacitance. Finally, we compute the approximate collective resonance frequency for charge oscillations in the dot and discuss the possibility of plasmon coupling to single-electron tunneling.

 

100.    K. Sugii, S. Ishizawa, Y. Kobayashi, H. Hibino, and M. Seki

            "Tem Moire Pattern And Scanning Auger-Electron Microscope Analysis Of Anomalous Si Incorporation Into Mbe-Grown Ge On Si(111)"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 31 (10), 3296-3300 (1992).

 

            ABSTRACT: Ge islands are grown by molecular beam epitaxy (MBE) on Si(111) surfaces with an SPE-grown buffer layer, which was expected to prevent intermixing between the epitaxial Ge layer and the Si substrate. The epilayer composition analyzed from the spacing of the Moire fringe indicates that the Ge islands should be a Si-Ge alloy rather than pure Ge and that the alloying of Ge with Si is greater near the edges of the island. The alloying phenomenon was verified by the compositional depth profile analysis using the scanning Auger electron microscope (SAM) technique. The Si incorporation into the Ge islands observed here cannot be explained by a bulk diffusion mechanism and is a seriously anomalous phenomenon since Si diffusion into Ge would be negligible at the growth temperature and time used ill this experiment.

 

101.    K. Sugiyama, O. Kondo, F. Tomiyama, M. Date, Y. Hidaka, T. Ishii, and A. Matsuda

            "Magnetizations Of R2cuo4(R=Nd,Pr,Gd) Single-Crystals"

            J. Magn. Magn. Mater. 104, 1223-1224 (1992).

 

            ABSTRACT: High-field magnetizations of R2CuO4 (R = Nd, Pr and Gd) single crystals are investigated up to 36 T at low temperatures. Nd2CuO4 shows two anomalous phase transitions at 2.2 and 4.2 T along the [100] direction. The keyword to solve these transitions is the staggered field due to the Cu spin. Pr2CuO4 shows weak linear magnetization reflecting the singlet ground state of the Pr ion. Gd2CuO4 shows an anomalous but systematic multistep magnetization with a magnitude of each step of about 10(-3)-mu-B per Gd ion in the c-plane beside the typical antiferromagnetic magnetization with small anisotropy. The origin is not clear.

 

102.    D. Sun and Y. Yamamoto

            "Passive Stabilization Of A Synchronously Pumped External-Cavity Surface-Emitting Ingaas/Inp Multiple Quantum-Well Laser By A Coherent Photon-Seeding Technique"

            Appl. Phys. Lett. 60 (11), 1286-1288 (1992).

 

            ABSTRACT: A synchronously pumped external-cavity surface-emitting InGaAs/InP multiple quantum well laser was passively stabilized by a coherent photon-seeding technique using an integrated output-coupling mirror. Both pulse duration and spectral width were reduced significantly and the time-bandwidth product was reduced by a factor of 30 to a near transform-limited value.

 

103.    D. C. Sun, S. R. Friberg, K. Watanabe, S. Machida, Y. Horikoshi, and Y. Yamamoto

            "High-Power And High-Efficiency Vertical Cavity Surface Emitting Gaas-Laser"

            Appl. Phys. Lett. 61 (13), 1502-1503 (1992).

 

            ABSTRACT: We report high power and high efficiency operation of a vertical cavity surface emitting GaAs laser in an external cavity. The maximum cw output power from the fundamental TEM00 mode was 700 mW at a temperature of 77 K when pumped by a cw krypton-ion laser with 1.8 W pump power. We obtained an absolute quantum efficiency (pump photons to lasing photons) of 44%, and a differential efficiency above threshold of 58%.

 

104.    M. Suzuki and T. Fukuda

            "Observation Of Indium On Gaas(110) Surfaces By Scanning Tunneling Microscopy"

            Ultramicroscopy 42, 858-863 (1992).

 

            ABSTRACT: The surface structure of indium overlayers on cleaved p-type GaAs(110) is studied by scanning tunneling microscopy in ultrahigh vacuum. About 1 monolayer of indium was deposited on the surfaces at room temperature. We observed two types of indium adsorption. One is linear clusters along the [110BAR] direction with corrugation amplitudes 1-2 angstrom above the GaAs surface. The other type, in which the second-layer indium atoms adsorb on the four-fold hollow site of the first-layer indium atoms, is also obtained near the linear islands. It is found that an In atom favors a Ga site rather than an As site for both types of adsorption.

 

105.    H. Tabei, T. Horiuchi, O. Niwa, and M. Morita

            "Highly Sensitive Detection Of Reversible Species By Self-Induced Redox Cycling"

            J. Electroanal. Chem. 326 (1-2), 339-343 (1992).

 

            ABSTRACT:

106.    H. Tabei, M. Morita, O. Niwa, and T. Horiuchi

            "Fabrication And Electrochemical Features Of New Carbon Based Interdigitated Array Microelectrodes"

            J. Electroanal. Chem. 334 (1-2), 25-33 (1992).

 

            ABSTRACT: A new type of interdigitated array (IDA) microelectrode based on carbon film was developed. A conductive carbon film was prepared on a platinum coated Si wafer by the pyrolysis of 3,4,9,10-perylenetetracarboxylic dianhydride. The IDA microelectrode was fabricated by photolithographic techniques from the carbon/platinum composite film. The IDA electrode had 50 microband pairs. The width of each microband was 3-mu-m with a length of 2 mm, and the gap between two electrode bands was 2-mu-m. The electrode was characterized by cyclic voltammetry with water soluble ferrocene and ruthenium hexa-amine. The potential window without redox species was found to be similar to that of a conventional glassy carbon electrode. The IR drop was negligible in a measurement with 10-mu-M water soluble ferrocene at a moderate scan rate. Generation-collection voltammograms of water soluble ferrocene and ruthenium hexa-amine show clear limiting currents and their response in the negative potential range was superior to that of conventional metal film IDA electrodes.

 

107.    A. Taguchi, M. Taniguchi, and K. Takahei

            "Direct Verification Of Energy Back Transfer From Yb 4f-Shell To Inp Host"

            Appl. Phys. Lett. 60 (8), 965-967 (1992).

 

            ABSTRACT: We report direct verification of energy back transfer from a Yb 4f-shell to an InP host, which has been proposed as a quenching mechanism for the intrinsic thermal quenching of intra-4f-shell luminescence. Photoluminescence time decay of the band-edge related luminescence for a Yb-doped InP sample was examined. In the temperature region from 100 to 120 K, it was observed that the luminescence time-decay curve is composed of two exponential decay components. The decay-time constant of the slower component in the band-edge related luminescence is the same as that in the Yb 4f-shell luminescence. This fact clearly shows that there is an energy transfer between the Yb 4f-shell electronic state and the InP host electronic state, and the energy back-transfer mechanism is the cause of the intrinsic thermal quenching of the Yb intra-4f-shell luminescence.

 

108.    T. Takagahara

            "Quantum Dot Lattice And Enhanced Excitonic Optical Nonlinearity"

            Surf. Sci. 267 (1-3), 310-314 (1992).

 

            ABSTRACT: We propose a concept of quantum dot lattice for enhancing the excitonic optical nonlinearity, especially its figures of merit. The most important aspect of the quantum dot lattice for enhancing the optical nonlinearity is the enlarged exciton coherence length due to the cooperation of a large number of quantum dots. The optical nonlinearity of the quantum dot lattice composed of typical semiconductor materials is estimated and an enhancement in the figures of merit of several orders of magnitude over the ever known values is predicted.

 

109.    T. Takagahara and K. Takeda

            "Theory Of The Quantum Confinement Effect On Excitons In Quantum Dots Of Indirect-Gap Materials"

            Phys. Rev. B 46 (23), 15578-15581 (1992).

 

            ABSTRACT: The quantum confinement effect on excitons in quantum dots of indirect-pp materials is investigated and a mechanism that induces an indirect-to-direct conversion of the character of the optical transition is clarified. The exciton transition energy and the exciton binding energy are calculated and found to be in good agreement with experimental results on Si and Ge nanostructures. The large exciton binding energy in Si and Ge quantum dots suggests that the photoluminescence from these nanostructures is of excitonic origin even at room temperature. The estimated radiative lifetime of excitons is strongly size dependent and varies from nanosecond to millisecond corresponding to the diameter from approximately 10 to approximately 30 angstrom. These theoretical results suggest strongly the importance of the quantum confinement effect in the luminescence processes of porous Si.

 

110.    S. Takagi, M. Kimura, and M. Katsuki

            "A Rapid And Efficient Protocol Of The Inverted Pcr Using 2 Primer Pairs"

            Biotechniques 13 (2), 176-178 (1992).

 

            ABSTRACT:

111.    M. Takahashi, M. Morita, O. Niwa, and H. Tabei

            "Highly Sensitive High-Performance Liquid-Chromatography Detection Of Catecholamine With Interdigitated Array Microelectrodes"

            J. Electroanal. Chem. 335 (1-2), 253-263 (1992).

 

            ABSTRACT: Interdigitated array (IDA) microelectrodes in which both the band width and gap are 2 mum were fabricated and applied to the electrochemical detectors used in flow injection analysis (FIA) and high-performance liquid chromatography (HPLC). The steady-state limiting current measured by FIA consists of the one-third power flow dependent current and the flow independent current. This flow independent current is caused by redox cycling. When an IDA electrode is used, the current density is about ten times greater than with an ordinary glassy carbon disk electrode. The high current density and low background noise allowed the detection of 100 pM (2 fmol) of dopamine by HPLC measurement. It was found that the peak current and sample concentration had a linear relationship over a wide range (from 100 pM to 10 muM).

 

112.    K. Takahei and H. Nakagome

            "Photoluminescence Characterization Of Nd-Doped Gap Grown By Metalorganic Chemical Vapor-Deposition"

            J. Appl. Phys. 72 (8), 3674-3680 (1992).

 

            ABSTRACT: Nd-doped GaP is grown by metalorganic chemical vapor deposition and characterized by photoluminescence measurements. The liquid-helium-temperature luminescence spectra due to Nd intra-4f-shell transitions depend on the growth conditions of the crystals. Some crystals show only a small number of luminescence lines, while some other crystals show many luminescence lines, indicating the presence of many kinds of Nd light emitting centers. Intensities of some luminescence lines begin to decrease at about 50 K and they are below the detection limit at 100 K. However, thermal quenching of some other luminescence lines begins at higher temperatures and their luminescence can be observed up to room temperature. A study on photoexcitation with above and below-band gap energy photons reveals that some Nd centers can be excited even by below-band gap energy photons, indicating the role of mid-pp levels, in the excitation mechanism, related to the Nd centers. A further comparative study of luminescence characteristics on GaP and GaAs doped with Nd shows that the experimental evidence is consistent with the excitation mechanism proposed for intra-4f-shell luminescence of Yb in InP, where the rare earth 4f shells are excited by way of electron-hole recombination at rare-earth-related trap levels with successive energy transfer.

 

113.    K. Takeda and K. Shiraishi

            "Electronic-Structure Of Chain-Like Polystannane"

            Chem. Phys. Lett. 195 (2-3), 121-126 (1992).

 

            ABSTRACT: The electronic structure of polystannane (PSn), (SnH2)n, has been calculated by the first principle local density functional method. The effect of bond-angle distortion on PSn's first band gap is also investigated theoretically. The common features in the group IV polymers are then summarized by comparison with previous calculated results for polysilane (SiH2)n and polygermane (GeH2)n.

 

114.    K. Takeda and K. Shiraishi

            "1st-Principles Calculations On Adiabatic Potential Surfaces Of Hydrogen-Atoms In Polysilane"

            Philos. Mag. B-Phys. Condens. Matter Stat. Mech. Electron. Opt. Magn. Prop. 65 (3), 535-552 (1992).

 

            ABSTRACT: Adiabatic potential surfaces are calculated for an H atom at various positions in polysilane. The calculations are based on local-density-functional theory, using pseudo-potentials, in a supercell geometry. The migration paths for a H atom dissociated from the side-chain position, and for a foreign H atom are investigated. One possible path entwines the Si skeleton. Bond switching due to breaking the Si-H bond and the ensuing H migration is also discussed on the basis of three hypothetical atomic configurations.

 

115.    K. Takei and Y. Maeda

            "Nmr-Study On Compositional Distribution In Sputter-Deposited Co-Ni Thin-Films"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 31 (9A), 2734-2735 (1992).

 

            ABSTRACT: Compositional distribution in sputter-deposited Co-Ni films was measured by using spin echo Co-59 NMR. The NMR frequency spectra of Co-Ni films were very similar to those of compositionally homogeneous Co-Ni powdered alloys. A simulation of the NMR spectra indicated that the Co-Ni films were in a compositionally homogeneous state in which the Co and Ni were distributed randomly at the lattice sites.

 

116.    M. Taniguchi, H. Nakagome, and K. Takahei

            "Luminescence Lifetime Studies Of Nd-Doped Gap And Gaas"

            J. Lumines. 52 (5-6), 251-257 (1992).

 

            ABSTRACT: Photoluminescence time decay experiments are performed for the first time at liquid helium temperature on Nd-doped GaP samples which show sharply structured (1-mu-m) luminescence spectra due to Nd-intra-4f-shell transitions. It is found that the luminescence lifetimes are different for luminesence lines originating from different Nd centers. The observed 4 K lifetimes (16-20-mu-s) are longer than the 77 K lifetime (5-mu-s) previously observed from an ion-implanted GaP:Nd sample. The temperature dependence of the luminescence lifetime is also reported. A similar lifetime value of 12-mu-s is observed from a GaAs: Nd sample at 4 K. These intrinsic 4 K lifetimes of Nd in GaP and GaAs are shorter than the lifetimes of Nd in II-VI compounds and ionic crystals. It is probably due to the stronger covalent bonding between Nd ions and the host crystals or the lower symmetry of Nd sites in GaP and GaAs hosts.

 

117.    S. Tarucha, Y. K. Fukai, Y. Hirayama, and T. Saku

            "Ballistic Electron Propagation In Macroscopic 4-Terminal Structures And Its Gate Controlled Transmission And Reflection"

            Surf. Sci. 263 (1-3), 253-257 (1992).

 

            ABSTRACT: Ballistic electron transport in macroscopic four-terminal devices with a high electron mobility is studied. The bend resistance characteristics are well analyzed using the Landauer-Buttiker formula although the leads are too wide to form well-defined one-dimensional subbands. The ballistic length determined from this analysis agrees well with the mean free path deduced from a mobility and electron density. Transmission and reflection of ballistic electrons are manipulated using a strip gate placed so as to bisect the device. The transmission and reflection probabilities are determined as a function of gate voltage, and related to the change in the refraction of ballistic electron propagation across the regions of different electron densities.

 

118.    S. Tarucha, T. Saku, Y. Hirayama, and Y. Horikoshi

            "Bend-Resistance Characteristics Of Macroscopic 4-Terminal Devices With A High Electron-Mobility"

            Phys. Rev. B 45 (23), 13465-13468 (1992).

 

            ABSTRACT: Bend-resistance characteristics are studied for four-terminal ballistic devices with a high electron mobility on a macroscopic scale of order 10-100-mu-m. The negative bend resistance induced by ballistic electron transport is quantitatively reproduced by the Landauer-Buttiker formula in the classical limit for various device sizes and electron densities. Using this formula, we determine the ballistic electron length as a function of electron density, which compares well with the elastic mean free path deduced from the electron mobility and electron density.

 

119.    S. Tarucha, T. Saku, Y. Hirayama, J. R. Phillips, K. Tsubaki, and Y. Horikoshi

            "Ballistic Transport And Low-Frequency Noise In High-Mobility 2-Dimensional Electron-Systems"

            Inst. Phys. Conf. Ser. (127), 127-132 (1992).

 

            ABSTRACT: Ballistic transport and low-frequency noise are studied for two-dimensional electrons of very high electron mobility. Using macroscopic-scale devices, we reveal two major properties of ballistic transport: long-distance ballistic transport of electrons and size-independent resistance. These behaviors are well reproduced by the Landauer-Buttiker formula in the classical limit. We observe critical noise generation for a large injection current in a wide channel device. This arises from nonequilibrium electron heating under high electric field.

 

120.    H. Teramae

            "Electronic-Properties Of Polymeric Silicon Hydrides - Comment"

            Phys. Rev. B 46 (19), 12788-12789 (1992).

 

            ABSTRACT: The electronic structure of the polysilene chain is studied by means of the ab initio crystal orbital calculations. The electronic structure of polysilene is not metallic at the Hartree-Fock level and the effect of the inclusion of the d orbitals on silicon is small. These conclusions are completely different from the recent work of Springborg.

 

121.    Y. Tokura, T. Saku, S. Tarucha, and Y. Horikoshi

            "Anisotropic Roughness Scattering At A Heterostructure Interface"

            Phys. Rev. B 46 (23), 15558-15561 (1992).

 

            ABSTRACT: Anisotropic Hall mobilities of a two-dimensional electron gas are observed in modulation-doped AlxGa1-xAs/GaAs heterostructures grown by molecular-beam epitaxy on a (001) GaAs substrate. The mobility in the [110BAR] direction is larger than that in the [110] direction. An anisotropic in roughness is proposed to account for the observed anisotropic Hall mobilities.- The dependences of the anisotropic mobilities on the electron concentration are explained well by the theoretical calculation, which assumes the existence of interface islands longer in the [110BAR] direction than in the [110] direction. This assumption is consistent with previous reports on in situ measurement of growing surfaces by scanning tunneling microscope and electron diffraction.

 

122.    K. Tsubaki, T. Honda, H. Saito, and T. Fukui

            "Electron Wave Interference In Fractional Layer Superlattice (Fls) Quantum Wires"

            Inst. Phys. Conf. Ser. (120), 619-624 (1992).

 

            ABSTRACT:

123.    K. Tsubaki, T. Honda, H. Saito, and T. Fukui

            "Density Of States Of Alas/Gaas Fractional Layer Superlattice Quantum Wires In A Modulation Doped Structure"

            Surf. Sci. 267 (1-3), 270-273 (1992).

 

            ABSTRACT: The density of states (DOS) of AlAs/GaAs fractional layer superlattice (FLS) quantum wires is found to consist of one-dimensional and zero-dimensional states. The FLS quantum wires are fabricated by electron beam lithography from the AlAs/GaAs FLS modulation doped heterostructure. The periodicity of the FLS quantum wires is 8 nm and the width is 0.25-mu-m. Drain current oscillations with negative transconductance is observed below 7.5 K due to a reduction in wire width. The density of states is estimated from the temperature dependence of the threshold voltage (V(th)). Since the DOS of the FLS quantum wire structure has sharper peaks than that of the unconfined FLS modulation-doped structure, which has both one-dimensional and two-dimensional electron states, we can conclude that the additional sub-micron confinement reduces these states to zero-dimensional and one-dimensional, respectively.

 

124.    K. Tsubaki, T. Honda, and Y. Tokura

            "Aharonov-Bohm Effect Under High Magnetic-Field In A Corbino Disk Antidot Channel"

            Surf. Sci. 263 (1-3), 392-395 (1992).

 

            ABSTRACT: Corbino disk anti-dots are fabricated by distributing several thousand sub-mu-m square holes throughout a square Corbino disk channel. The magnetoresistance (magnetoconductance) or Corbino disk anti-dots up to 10 T displays a periodic oscillation over the entire magnetic field at temperatures below 0.1 K. Since Corbino disk anti-dots prevent electrons from flowing along an edge, electrons go around the shallow etched holes under a high magnetic field. The periodic oscillation comes from the Aharonov-Bohm (A-B) effect, which is the electron wave interference of electron trajectories encircling the magnetic flux which penetrates through the shallow-etched hole.

 

125.    H. Tsubokawa, K. Oguro, H. P. C. Robinson, T. Masuzawa, T. Kirino, and N. Kawai

            "Abnormal Ca2+ Homeostasis Before Cell-Death Revealed By Whole Cell Recording Of Ischemic Ca1 Hippocampal-Neurons"

            Neuroscience 49 (4), 807-817 (1992).

 

            ABSTRACT: Slices were made from the hippocampus of gerbils following transient ischemia achieved by clamping the carotid arteries for 5 min, and changes in the electrophysiology of CA1 pyramidal neurons were studied by whole cell patch-clamp recording as well as conventional intracellular recording. The great majority of CA1 neurons in slices made 2.5-3 days after ischemia showed reduced resting potentials and were easily depolarized by prolonged low-frequency stimulation or by tetanic stimulation of the Schaffer collateral/commissural input. This stimulus-induced depolarization was accelerated by intracellular injection of D-Myo-inositol 1,4,5-triphosphate, which depolarized membrane potentials towards 0 mV without synaptic input stimulation. Intracellular application of BAPTA, a Ca2+ chelator, effectively blocked the stimulus-induced depolarization. When recording from ischemic neurons with patch pipettes containing both D-Myo-inositol 1,4,5-triphosphate and BAPTA, excitatory postsynaptic currents were transiently potentiated by stimulation, but the membrane potential did not show stimulus-induced depolarization and remained steady for long periods. These results lend support to the view that the intracellular Ca2+ regulation system is severely disturbed following ischemia, and that input fiber stimulation leads to abnormal Ca2+ accumulation in ischemic neurons resulted in neuronal death. The reduction of free Ca2+ inside the ischemic neuron by BAPTA apparently saves neurons which are otherwise destined to delayed neuronal death.

 

126.    M. Ueda, N. Imoto, H. Nagaoka, and T. Ogawa

            "Continuous Quantum-Nondemolition Measurement Of Photon Number"

            Phys. Rev. A 46 (5), 2859-2869 (1992).

 

            ABSTRACT: This paper presents a general theory for a continuous quantum-nondemolition measurement of photon number. This theory treats a time-distributed measurement as a sequence of measurements in which at most one photon can be detected in an infinitesimal time, and shows that the average number of photons remaining in the measured field increases when a photon is detected and decreases when no photon is detected. The state of the measured system evolves nonunitarily and reduces continuously to a number state whose eigenvalue is uniquely determined by the average rate of photodetection and whose probability distribution coincides with the initial photon-number distribution. Applying the general theory to typical quantum states - coherent, thermal, and squeezed states - shows that the continuous-state reduction towards a number state depends strongly on the initial photon statistics. Despite the nonunitarity of state evolution, an initially pure state keeps its purity: the initial density operator becomes diagonalized only if the readout information is discarded.

 

127.    M. Ueda and M. Kitagawa

            "Reversibility In Quantum Measurement Processes"

            Phys. Rev. Lett. 68 (23), 3424-3427 (1992).

 

            ABSTRACT: A measurement process is logically reversible if the premeasurement density operator of the measured system can be calculated from the postmeasurement density operator and the readout of the measuring apparatus. We show that the continuous-measurement version of a quantum counter, unlike the conventional photon counter, performs a logically reversible measurement. The physical origin for such a distinction is found to be sensitivity to vacuum field fluctuations.

 

128.    M. Ueda and S. Kurihara

            "Infrared Divergence In Single-Electron Tunneling"

            Phys. Rev. B 46 (19), 12568-12572 (1992).

 

            ABSTRACT: In small-capacitance normal tunnel junctions, even a single-electron tunneling causes a substantial change in the localized Coulomb potential. If the perturbation may be regarded as static, Fermi liquid theory requires that infinitely many electron-hole pairs should be excited near the Fermi surface. It is shown that such infrared divergence leads to a power-law anomaly in tunneling conductance. Possible experimental situations to observe this effect are discussed.

 

129.    T. Wakahara, H. Murase, and K. Odaka

            "Online Handwriting Recognition"

            Proc. IEEE 80 (7), 1181-1194 (1992).

 

            ABSTRACT: On-line handwriting recognition means that a machine recognizes each character as it is being written. For large-alphabet languages, like Japanese, handwriting input using an on-line recognition technique is essential for input accuracy and speed. It offers several advantages over off-line handwriting recognition. However, there are serious problems that prevent high recognition accuracy without imposing handwriting constraints. First, the thousands of ideographic Japanese characters of Chinese origin (called Kanji) can be written with wide variations in the number and order of strokes and significant shape distortions. Also, writing box-free recognition of characters is required to create a better man-machine interface. This paper describes the intense research performed by NTT over the past 15 years to answer the most pressing recognition problems. Prototype systems developed by NTT are also described. Last, the man-machine interfaces made possible with on-line handwriting recognition and anticipated advances in both hardware and software are discussed.

 

130.    M. Weyers, M. Sato, and H. Ando

            "Red Shift Of Photoluminescence And Absorption In Dilute Gaasn Alloy Layers"

            Jpn. J. Appl. Phys. Part 2 - Lett. 31 (7A), L853-L855 (1992).

 

            ABSTRACT: We present the first report on the optical properties of dilute GaAS1-xNx alloys (0<x<0.015). The layers have been grown by plasma-assisted metalorganic chemical vapor deposition (MOCVD). The grown layers show a systematic red shift of the band-edge luminescence with increasing N content. The assignement of the phoyoluminescence to band-edge transitions and not to isolated N-N pair emission is verified by the characteristics of the optical absorption.

 

131.    M. Weyers and K. Shiraishi

            "Carbon In Iii-V Compounds - A Theoretical Approach"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 31 (8), 2483-2487 (1992).

 

            ABSTRACT: Carbon as a very well behaved acceptor dopant in GaAs/AlGaAs is already successfully used in many device applications. However, the physics governing its incorporation behavior (amphoteric impurity) into III-V semiconductors is currently not well understood. We present a calculation from first principles of the change in total energy accompanying the incorporation of carbon onto lattice sites in the III-V compounds AIP, GaP, InP; and AlAs, Ga.As and InAs. Taking into account the energy gained by filling a group III or group V vacancy with carbon, the obtained p-type conduction in carbon doped GaAs, AlAs, GaP (and presumably AlP) as well as the n-type conduction in InP can be explained based on the results of our total energy calculations. Additionally, the observed trends in the energy gain can explain the observed differences in tendency for carbon incorporation into the compounds under study.

 

132.    K. Winer

            "Behavior Of Excess As In Nonstoichiometric Si-Doped Gaas"

            J. Appl. Phys. 71 (12), 5841-5846 (1992).

 

            ABSTRACT: The Si doping efficiency (=[e-]/[Si]) in homoepitaxial GaAs has been measured as a function of molecular beam epitaxial growth conditions (As pressure, substrate temperature, and growth rate) and post-growth thermal annealing conditions. The doping efficiency decreases from one under optimal growth conditions to almost zero: (1) exponentially with inverse substrate temperature below 400-degrees-C and (2) as a power law in the As4-to-Ga beam-equivalent fluence ratio above unity. The doping efficiency of nonoptimally grown films increases from almost zero to near one upon post-growth thermal annealing above 650-degrees-C with slower than exponential kinetics. These changes are attributed to charge trapping into and release from, respectively, excess-As-related defects, which are incorporated during growth and removed by out-diffusion during annealing.

 

133.    S. Yamada, H. Asai, and Y. Kawamura

            "Subband Effective Mass And Mobility Of 2-Dimensional Electrons In Uniformly Si-Doped Ga0.47in0.53as/Al0.48in0.52as Multiple Quantum-Wells"

            J. Appl. Phys. 72 (2), 569-574 (1992).

 

            ABSTRACT: Subband effective mass and mobility of a two-dimensional electron gas in uniformly Si-doped Ga0.47In0.53As/Al0.48In0.52As multiple quantum wells are estimated. In three samples with well widths of 130, 200, and 300 angstrom and a fixed barrier width of 68 angstrom, up to three two-dimensional subbands are found. Maximum enhancement of electron effective mass is 25% over the bulk value at a Fermi energy of 108 meV. These estimated effective masses are slightly smaller than previously reported values, and this is explained by recent theories which assume only nonparabolic correction. When the temperature ratio, (Dingle temperature)/(mobility temperature), is assumed to be identical in different subbands in each sample, the electron mobility of the first excited subband is at most twice that of the ground subband in the sample with the widest well. The effects of intersubband scattering and of screening on the subband mobilities are also discussed.

 

134.    S. Yamada and M. Yamamoto

            "Possible Conductance Quantization In Narrow Wires With Point-Contact Boundaries"

            Phys. Rev. B 45 (24), 14162-14166 (1992).

 

            ABSTRACT: Longitudinal conductance in quasiballistic narrow wires reveals plateaus if the wires have point-contact (PC) boundaries. When two PC boundaries defining a quasiballistic wire are opposite each other and weakly coupled, the conductance difference between the successive plateaus is almost constant under zero and relatively low magnetic fields and the magnitude is likely DELTA-G approximately f(c)(2e2/h), where f(c) is a constant less than 1. This value changes, depending on the wire conductance and on the differences in electrical characteristics between the two PC's. The origin of the appearance of the plateaus is also discussed briefly.

 

135.    S. Yamada and M. Yamamoto

            "Direct Estimation Of Quantized Thermopower In A Single Point Contact"

            Semicond. Sci. Technol. 7 (3B), B289-B291 (1992).

 

            ABSTRACT: The quantized thermopower in the ballistic regime was estimated directly from measurements in a single point contact with a specific configuration of ohmic electrodes. If the DC current supplied to heat electrons increased over a critical value, increases of both the electron and lattice temperatures were observed. For the lower indices of the one-dimensional subbands (i = 1 and 2), the measured thermopower peak differed by as much as 20% from the theoretically predicted value. At low currents, where only the electron temperature was raised, the agreement with theory was within 10%.

 

136.    S. Yamada, M. Yamamoto, and K. Aihara

            "Quantum Oscillations Of Transverse Resistance In Series And Single Point-Contact Configurations"

            Surf. Sci. 263 (1-3), 265-269 (1992).

 

            ABSTRACT: We report in this work quantum oscillations in transverse resistance in series and single point-contact (PC) configurations. In the series case, both under zero and finite magnetic fields, an oscillation corresponding to the plateaus of the longitudinal resistance was observed. In the single PC with an accurate structure symmetry, a similar oscillation appeared only when a finite magnetic field was applied. In addition, it is confirmed that the oscillations occur at equilibrium conditions and their polarity is odd against reversal of the current direction. These results indicate a new and equilibrium origin of the oscillation, which is different from the oscillatory thermopower.

 

137.    H. Yamaguchi and Y. Horikoshi

            "As Desorption From Gaas And Inas Surfaces Studied By Improved High-Energy Electron Reflectivity Measurements"

            Appl. Surf. Sci. 60-1, 224-227 (1992).

 

            ABSTRACT: The electron beam specular reflectivity of GaAs and InAs (001) surfaces at several temperatures was quantitatively evaluated by measuring the current through an electrode in front of the fluorescence screen. At the reconstruction transition, the reflectivity as a function of substrate temperature changes discontinuously with a hysteresis cycle for InAs and changes continuously without a hysteresis for GaAs. This difference indicates that the order of surface structure transition differs between these two surfaces. The reflectivity changes during As desorption show that the desorption process is sensitive to surface structure transition and that the desorption at the structure transition differs between different orders of surface structure transitions.

 

138.    H. Yamaguchi and Y. Horikoshi

            "Growth Of Gaas/Eras/Gaas Structures By Migration-Enhanced Epitaxy"

            Appl. Phys. Lett. 60 (19), 2341-2343 (1992).

 

            ABSTRACT: Monocrystalline GaAs/ErAs/GaAs structures are fabricated by migration-enhanced epitaxy at 320-degrees-C. When the ErAs layer thickness is less than 3 monolayers, reflection high-energy electron diffraction patterns, double crystal x-ray diffraction analysis, and transmission electron microscopy observations show successful overgrowth of GaAs on the ErAs layer. Distinct satellite peaks are observed in an x-ray rocking curve of an ErAs/GaAs superlattice grown under a similar condition, indicating that high-quality multilayer structures with very thin ErAs layers can be fabricated by migration-enhanced epitaxy.

 

139.    H. Yamaguchi and Y. Horikoshi

            "As Desorption From Gaas And Alas Surfaces Studied By Improved High-Energy Electron Reflectivity Measurements"

            J. Appl. Phys. 71 (4), 1753-1759 (1992).

 

            ABSTRACT: The desorption of As from GaAs (001), (111)B, and AlAs(001) is studied in detail by measuring the electron-beam current reflected from these surfaces. When the As supply to the surface was terminated, the electron specular reflectivity decreases exponentially with time due to the As desorption. The decay rate was much smaller for AlAs (001) than for GaAs (001) and (111)B, which indicates stronger atomic bonding for AlAs than for GaAs. For the GaAs (001) surface, the decay rate and the activation energy for the decay in specular reflectivity change discontinuously at the transition between (2 x 4) and (3 x 1) reconstructions. This shows the As desorption process is sensitive to the transition of surface reconstruction. The dependence of the As desorption rate on the thickness of the top GaAs layer in GaAs/AlAs heterostructures indicates an abrupt change of bond strength near the interface.

 

140.    H. Yamaguchi and Y. Horikoshi

            "1st-Order Surface-Structure Transition On The (001) Inas Surface Studied With Improved High-Energy Electron Reflectivity Measurements"

            Phys. Rev. B 45 (3), 1511-1513 (1992).

 

            ABSTRACT: The electron-beam specular reflectivity of an InAs(001) surface was quantitatively measured as current through an electrode at several substrate temperatures. The reflectivity changes discontinuously at the reconstruction transition from As-stable (2 x 4) to In-stable (4 x 2) with hysteresis cycle as a function of the substrate temperature, indicating a first-order transition. The reflectivity change during As desorption shows that the desorption rate has a local minimum at the transition because of the existence of a metastable state due to the first-order transition.

 

141.    Y. Yamamoto and H. A. Haus

            "Effect Of Electrical Partition Noise On Squeezing In Semiconductor-Lasers"

            Phys. Rev. A 45 (9), 6596-6604 (1992).

 

            ABSTRACT: Amplitude fluctuations in the light from a laser and the partition noise attributable to a beam splitter are analyzed using an equivalent-circuit model that incorporates amplitude squeezing. When the energy is not carried by photons but by electrons and also when electrons can be treated as classical particles, the circuit model need not be changed. One simply applies the general circuit model to low frequencies h-nu << k(B)T. Conversion of an electric current to photon flux, and vice versa, converts classical sub-shot-noise spectra of electric currents into quantum squeezing of photon fluxes, and vice versa. The sub-shot-noise character of electric currents, unlike that of quantum squeezing, is not necessarily destroyed by current loss.

 

142.    Y. Yamamoto, S. Machida, and G. Bjork

            "Cavity Quantum Electrodynamics In Quantum-Well Lasers"

            Surf. Sci. 267 (1-3), 605-611 (1992).

 

            ABSTRACT: The physics and applications of cavity quantum electrodynamics in semiconductor lasers are discussed. Spontaneous emission from a quantum well was drastically modified by the microcavity structure. The increase in the coupling efficiency of spontaneous emission into a cavity resonant mode leads to the reduction of the threshold current. Oscillation without inversion is possible if the coupling efficiency is increased to close to one.

 

143.    Y. Yamamoto, S. Machida, and G. Bjork

            "Micro-Cavity Semiconductor-Lasers With Controlled Spontaneous Emission"

            Opt. Quantum Electron. 24 (2), S215-S243 (1992).

 

            ABSTRACT: The principle and applications of quantum electrodynamics in microcavity semiconductor lasers are reviewed. The coupling efficiency of spontaneous emission into a lasing mode and the spontaneous lifetime are modified by various microcavity structures. As a consequence of the increased coupling efficiency, those microcavity semiconductor lasers are expected to feature a low threshold current, high quantum efficiency and broad modulation bandwidth. One remarkable result of the increased coupling efficiency is 'lasing without inversion'. The other is 'intensity squeezing at any pump rate'.

 

144.    Y. Yamamoto, S. Machida, and W. H. Richardson

            "Photon Number Squeezed States In Semiconductor-Lasers"

            Science 255 (5049), 1219-1224 (1992).

 

            ABSTRACT: Electromagnetic fields, with the noise on one quadrature component reduced to below the quantum mechanical zero-point fluctuation level and the noise on the other quadrature component enhanced to above it, are currently of great interest in quantum optics because of their potential applications to various precision measurements. Such squeezed states of light are usually produced by imposing nonlinear unitary evolution on coherent (or vacuum) states. On the other hand, squeezed states with reduced photon number noise and enhanced phase noise are generated directly by a constant current - driven semiconductor laser. This is the simplest scheme for the generation of nonclassical light, and so far it has yielded the largest quantum noise reduction. The mutual coupling between a lasing junction and an external electrical circuit provides opportunities for exploring the macroscopic and microscopic quantum effects in open systems.

 

145.    Y. Yamamoto and S. Tarucha

            "Regulated Single Electron To Single Photon Conversion In A Constant-Current-Driven Pn Microjunction"

            Jpn. J. Appl. Phys. Part 2 - Lett. 31 (8B), L1198-L1201 (1992).

 

            ABSTRACT: The single electron-hole pair injection followed by the emission of a single photon is regulated with time separation tau = e/I in a constant-current-driven semiconductor pn microjunction. Oscillation of the junction voltage with a frequency f = I/e results from the coexistence of continuous uniform charging into a depletion layer via a high-impedance constant-current source and discrete thermionic emission of an electron into the active p-region. The principle is similar to the Coulomb blockade in an ultrasmall-capacitance tunnel junction. The proposed scheme is expected to open up an interesting new field of combined single electronics and single photonics.

 

146.    Y. Yamauchi and N. Kobayashi

            "Decomposition Process Of Alane And Gallane Compounds In Metal-Organic Chemical Vapor-Deposition Studied By Surface Photoabsorption"

            Jpn. J. Appl. Phys. Part 2 - Lett. 31 (9A), L1263-L1265 (1992).

 

            ABSTRACT: We used surface photo-absorption (SPA) to study trimethylamine alane (TMAA) and dimethylamine gallane (DMAG) decomposition processes on a substrate surface in metal-organic chemical vapor deposition. The decomposition onset temperatures of these group III hydride sources correspond to the substrate temperature at which the SPA reflectivity starts to increase during the supply of the group III source onto a group V stabilized surface. It was found that TMAA and DMAG start to decompose at about 150-degrees-C on an As-stabilized surface, which is much lower than the decomposition onsets of trialkyl Al and Ga compounds. Low temperature photoluminescence spectra exhibit dominant excitionic emissions for GaAs layers grown by DMAG at substrate temperatures above 400-degrees-C, indicating that carbon incorporation and the crystal quality deterioration due to incomplete decomposition on surface is much suppressed by using DMAG. A comparison of AlGaAs photoluminescence between layers by TMAA/triethylgallium and triethylaluminum/triethylgallium shows that the band-to-carbon acceptor transition is greatly reduced by using TMAA. TMAA and DMAG were verified to be promising group III sources for low-temperature and high-purity growth with low-carbon incorporation.

 

147.    T. Yanagawa, H. Nakano, Y. Ishida, and Y. Sasaki

            "Photodarkening Mechanism In Colored Filter Glasses"

            Opt. Commun. 88 (4-6), 371-375 (1992).

 

            ABSTRACT: It is clearly shown that a nanosecond pulse dye laser can provide the same photodarkening effect in colored filter glasses as a picosecond hybridly mode-locked dye laser. This suggests that the photodarkening mechanism is associated with a kind of solarization and a state of surface activation due to the production of a snowball comprised of impurity ions around CdSxSe1-x microcrystallites. It is also shown that the laser annealing effect is the same as the photodarkening effect.

 

148.    R. Yano, M. Mitsunaga, and N. Uesugi

            "Stimulated-Photon-Echo Spectroscopy.1. Spectral Diffusion In Eu3+ Yalo3"

            Phys. Rev. B 45 (22), 12752-12759 (1992).

 

            ABSTRACT: Systematic measurements of stimulated-photon-echo intensities as a function of the first-to-second (tau) and second-to-third (T) pulse separations allow the investigation of the dynamical properties of the spectral diffusion for the F-7(0)-D-5(0) transition of a cryogenic Eu3+:YAlO3 sample. The existence of spectral diffusion was verified by the significant broadening (from 1.2 to 7.2 kHz) of the homogeneous linewidth (GAMMA) as T increases from microseconds to milliseconds, the effect being attributed to the flip flop of nearby aluminum nuclear spins surrounding the Eu3+ ion. A similar broadening effect (from 0.61 kHz, to a few kHz) was also observed in the presence of a static magnetic field H0 = 137 G, but with a much slower diffusion rate. To explain these observations, we use three theoretical models: the Bai-Fayer model, the diffusion-equation model, and the Monte Carlo model. Each agrees reasonably well with the experimental data and indicates the flip rates of sub-kHz order at H0 = 0 and an order of magnitude lower at 137 G.

 

149.    R. Yano, M. Mitsunaga, and N. Uesugi

            "Nonlinear Laser Spectroscopy Of Eu3+Y2sio5 And Its Application To Time-Domain Optical Memory"

            J. Opt. Soc. Am. B-Opt. Phys. 9 (6), 992-997 (1992).

 

            ABSTRACT: Linear- and nonlinear-optical properties of Eu3+:Y2SiO5 have been investigated. All the energy levels of the 7F0,1,2. ground-state manifold and the 5D0,1,2 excited-state manifold were identified, and they were found to be doubly structured because of the two inequivalent optical sites. Two absorption lines of the 7F0-5D0 transition were studied in detail by using nonlinear spectroscopic techniques, photon-echo and stimulated-photon-echo methods. It was found by the photon-echo measurement that the optical dephasing time for one site is extremely long and is excitation-intensity dependent. With the smallest possible intensity we observed the longest ever dephasing time in a solid, 822-mu-s, or a 387-Hz homogeneous linewidth. From the stimulated-photon-echo measurement, the linewidth was found to be constant over a wide range of time scales, implying the absence of spectral diffusion in this crystal. These quite advantageous properties of this crystal were used for the demonstration of two novel types of time-domain optical data readout: time- and frequency-domain hybrid optical memory and spectrally programmed coherent transients.

 

150.    R. Yoshimura, H. Nakagome, S. Imamura, and T. Izawa

            "Coupling Ratio Control Of Polymeric Wave-Guide Couplers By Bending"

            Electron. Lett. 28 (23), 2135-2136 (1992).

 

            ABSTRACT: Directional couplers are successfully fabricated on acrylic substrates using polymers synthesised from deuterated methacrylate and deuterated fluoromethacrylate monomers. The excess loss of a 50 mm long coupler is about 0.7 dB including waveguide and fibre coupling losses. A novel method is proposed for tuning the coupling ratio. By bending the coupler, high precision control of within 1% is attained without optical polarisation dependence.

 

151.    S. Zhang and N. Kobayashi

            "Using Tertiary Butylamine For Nitrogen Doping During Migration-Enhanced Epitaxial-Growth Of Znse"

            Jpn. J. Appl. Phys. Part 2 - Lett. 31 (6A), L666-L668 (1992).

 

            ABSTRACT: We report the first use of tertiary butylamine as a nitrogen source for doping nitrogen into ZnSe. Tertiary butylamine cracked at various temperatures from 550 to 850-degrees-C was supplied onto ZnSe grown by migration-enhanced epitaxy. Photoluminescence of the doped ZnSe films indicated that nitrogen concentration increases with increasing cracking temperature. Secondary ion mass spectrometry revealed that a uniform nitrogen concentration as high as 8 x 10(18) cm-3 could be achieved. The results of site-selective doping onto Se and Zn surfaces during growth imply that nitrogen is more efficiently incorporated into ZnSe when the dopant is supplied at the same time that Se is supplied.

 

152.    S. Zhang and N. Kobayashi

            "X-Ray-Diffraction Study Of Annealed Znse/Gaas Superlattices"

            Appl. Phys. Lett. 60 (20), 2499-2501 (1992).

 

            ABSTRACT: We investigate the effect of annealing on the structural properties of ZnSe/GaAs superlattices by the x-ray double-crystal rocking-curve technique. A 6-period ZnSe/GaAs superlattice with 61-nm thick ZnSe layers and 6-nm thick GaAs layers is grown by a combination of migration-enhanced epitaxy and solid-phase epitaxy. X-ray diffraction is measured for the ZnSe/GaAs superlattice samples annealed at different temperatures for several annealing periods in flowing H-2 gas. From the change in the (004) and (115) rocking-curve profiles with increasing annealing temperature and annealing period, it was found that about 25% of the parallel strain in the ZnSe layers is relieved by misfit dislocations after annealing at 520-degrees-C for 20 min. The interface properties of the annealed ZnSe/GaAs superlattices are also examined by computer simulation of kinematical diffraction.

 

153.    S. Zhang and N. Kobayashi

            "Photoluminescence From Narrow Znse/Gaas/Znse Quantum-Wells"

            J. Cryst. Growth 117 (1-4), 1074-1074 (1992).

 

            ABSTRACT:

154.    S. Zhang and N. Kobayashi

            "Photoluminescence And Structure Properties Of Gaas/Znse Quantum-Wells"

            Appl. Phys. Lett. 60 (7), 883-885 (1992).

 

            ABSTRACT: By improving the quality of the GaAs well layer on a ZnSe barrier, we were able to observe the quantum size effect in photoluminescence of ZnSe/GaAs/ZnSe quantum wells. After solid phase epitaxy of 2-ML GaAs on ZnSe epilayer, migration-enhanced epitaxy (MEE) of the GaAs well layer was carried out while the growth temperature was elevated in steps. Photoluminescence from the obtained quantum wells has been appreciably improved by this method. The photoluminescence spectra show a systematic shift to higher energies as the well width is reduced, clearly demonstrating the size effect in the ZnSe-GaAs system. By comparing the experimental data with calculated emission energies, the valence-band and conduction-band discontinuities between ZnSe and GaAs in the <001> direction have been determined to be 1.27 +/- 0.02 and 0.03 +/- 0.02 eV, respectively.

 

155.    S. Zhang, N. Kobayashi, and Y. Horikoshi

            "Growth And Characterization Of Thin Znse/Gaas/Znse Quantum-Wells"

            Surf. Sci. 267 (1-3), 124-128 (1992).

 

            ABSTRACT: ZnSe/GaAs/ZnSe single quantum wells (QW's) with a well width as thin as 2 nm and 15-period ZnSe/GaAs (with a barrier width of 97 nm and a well width of 3 nm) multiple quantum wells have been successfully grown by Migration-Enhanced Epitaxy (MEE). The structures have been confirmed by transmission electron microscopy (TEM) and high-resolution scanning electron microscopy (SEM). It has been also revealed that the quantum well structures are formed coherently on the GaAs(001) substrate. Furthermore, emissions due to the quantum size effect in the ZnSe/GaAs system have been achieved in photoluminescence measurements.