1.         M. Akagi

            "Modeling Of Contextual Effects Based On Spectral Peak Interaction"

            J. Acoust. Soc. Am. 93 (2), 1076-1086 (1993).

 

            ABSTRACT: This paper presents a model of contextual effects able to cope with coarticulation problems, especially vowel neutralization. This model is designed to model the superior recognition ability mechanisms of humans and apply these mechanisms to automatic speech recognition and synthesis. It predicts target spectral peaks in reduced vowels, based on interactions between spectral peak pairs. To construct and substantiate the model, psychoacoustic experiments were carried out to measure the extent of phoneme boundary shift with a single formant stimulus as a preceding anchor. The results of the experiments were compared with the spectral peak interaction results obtained from real speech data using the model. This comparison showed that the obtained spectral peak interactions, measured through perceptual boundary shifts with a single formant anchor, are similar to the spectral peak interactions estimated by the model. Additionally, recovery simulations of reduced spectral peak trajectories with real speech data showed that the spectral peak interactions obtained from the psychoacoustic experiments can be used to predict target spectral peaks from reduced spectral peak trajectories in the same manner as the spectral peak interaction function estimated by the model. These results suggest that the model may be emulating aspects of the human mechanisms, that the contextual effects resulting from the interactions between single formant stimuli can play an important role in improving phoneme neutralization recovery, and that the neutralization recovery model can be formulated as the sum of the interactions between spectral peaks. Furthermore, the model can be implemented as a speech recognition preprocessor to reduce recognition error rates because it can overshoot spectral peak trajectories, shift spectral peaks toward their targets, and increase distances among category centers and Bhattacharyya distances between vowel categories.

 

2.         M. Amamiya, F. Mizoguchi, K. Hirata, and H. Yasukawa

            "Special Issue - Selected Papers From The International-Conference On 5th Generation Computer-Systems 1992 - Preface"

            New Gener. Comput. 11 (3-4), 223-225 (1993).

 

            ABSTRACT:

3.         H. Ando, S. Nojima, and H. Kanbe

            "Band-Edge Optical-Absorption Spectra Of Gaas Quantum Wires Calculated By Multiband Effective-Mass Theory"

            J. Appl. Phys. 74 (10), 6383-6390 (1993).

 

            ABSTRACT: Optical absorption spectra of quasi-1D GaAs quantum well wires are theoretically investigated within the framework of multiband effective mass theory. In the calculation, the mixing of heavy-hole and light-hole bands resulting from both ID quantum confinement and electron-hole Coulomb interaction is considered. Detailed excitonic structures in the absorption spectrum near the band edge are clarified by taking into account Coulombic bound states and unbound continuum states. Polarization dependence of the optical absorption spectra is discussed in terms of the band mixing effects.

 

4.         S. Ando, T. Honda, and N. Kobayashi

            "Self-Limited Facet Growth For Gaas Tetrahedral Quantum Dots"

            Jpn. J. Appl. Phys. Part 2 - Lett. 32 (1A-B), L104-L106 (1993).

 

            ABSTRACT: When metal-organic chemical vapor deposition is used to fabricate GaAs tetrahedral quantum dots by selective epitaxy on triangular windows of (111)B GaAs, there is a condition under which growth automatically stops before the tetrahedral shape is completed. Under a constant growth condition, the size of self-stopped (111)B triangular top facets is extremely uniform and is not influenced by fluctuation of mask window size. Experiments showing that the size of top facet increases with increasing substrate temperature and with decreasing trimethylgallium partial pressure imply that the size is determined by the submicron diffusion length of Ga atoms on (111)B GaAs surface.

 

5.         S. Ando, N. Kobayashi, and H. Ando

            "Novel Hexagonal-Facet Gaas/Algaas Laser Grown By Selective-Area Metalorganic Chemical-Vapor-Deposition"

            Jpn. J. Appl. Phys. Part 2 - Lett. 32 (9B), L1293-L1296 (1993).

 

            ABSTRACT: A GaAs hexagonal prism structure with (110) sidewall facets perpendicular to the (111)B substrate surface is obtained by selective area metalorganic chemical vapor deposition using a SiO2 mask. These (110) sidewall facets are extremely smooth like a cleaved surface, so they can be used as the cavities of a semiconductor laser. A novel hexagonal-facet (HF) GaAs/AlGaAs double heterojunction laser structure is proposed and preliminary lasing characteristics are presented. The average threshold of the optical pumping energy for the HF-laser array is approximately 18 pJ for 416 nm excitation. Single-mode (inscribed hexagonal mode) lasing at 875 nm is obtained at room temperature.

 

6.         T. Bever, G. Pfeiffer, T. Prescha, D. I. Bohne, J. Weber, A. D. Wieck, and K. Ploog

            "Deep-Level Transient Spectroscopy On Focused Ion-Beam Written Inplane Capacitances"

            J. Appl. Phys. 74 (10), 6088-6093 (1993).

 

            ABSTRACT: We discuss defects created by focused Ga ion beam implantation in GaAs or AlGaAs/GaAs heterostructures using deep level transient spectroscopy (DLTS). A novel contact configuration which is sensitive to defects located at the boundary between implanted and unperturbed regions at a well-defined depth is presented. The DLTS spectra for these samples are dominated by a peak with an activation energy of E(a) = 0.38 eV. The results show that this peak is associated with implantation-induced damage independent of the ion species. The defect is also found in a sample with Schottky contacts on top of a Ga-implanted Ga.As layer.

 

7.         T. Bever, K. Vonklitzing, A. D. Wieck, and K. Ploog

            "Velocity Modulation In Focused-Ion-Beam Written In-Plane-Gate Transistors"

            Appl. Phys. Lett. 63 (5), 642-644 (1993).

 

            ABSTRACT: The mobility of a one-dimensional electron gas can be changed markedly by moving the electron path from the high-mobility channel toward the low-mobility focused ion-beam-implanted regions. This can be done simply by applying different biases to the two adjacent in-plane gates. When the bias voltage on one gate is fixed, we increase the other gate potential and force the current path close to the ion-implanted region. In this way the mobility rather than the density of the carriers is controlled, which is the key feature of the velocity modulation transistors with inherently fast response.

 

8.         A. Chavezpirson, H. Ando, H. Saito, and H. Kanbe

            "Polarization Properties Of A Vertical-Cavity Surface-Emitting Laser Using A Fractional Layer Superlattice Gain Medium"

            Appl. Phys. Lett. 62 (24), 3082-3084 (1993).

 

            ABSTRACT: We investigate the polarization properties of a vertical cavity surface emitting laser that uses an (Al0.5Ga0.5As)1/2(GaAs)1/2 fractional-layer superlattice (FLS) as an anisotropic gain medium. The anisotropy in the gain enables us to both control and switch the polarization state of the optically pumped lasing output. We obtain room-temperature lasing for wavelengths from 690 to 720 nm. The output is linearly polarized and the polarization direction is fixed, either parallel or perpendicular to the FLS layers. By tuning the cavity resonance wavelength, we demonstrate high contrast switching between two orthogonal linear polarization states in the FLS surface emitting laser.

 

9.         J. L. Chern and K. Otsuka

            "Information-Theoretic Consideration Of The Chaotic Itinerancy In A Globally Coupled Laser Model"

            Phys. Lett. A 176 (3-4), 213-219 (1993).

 

            ABSTRACT: We apply information theory to the study of chaotic itinerancy in a globally coupled multimode laser model. Structure changes are found in the self-information flow, corresponding to switching among destabilized clustered states. The inhomogeneity in the self-information flows among modes shows that different information transport structures are created by cluster switching in chaotic itinerancy.

 

10.       J. L. Chern, K. Otsuka, and F. Ishiyama

            "Coexistence Of 2 Attractors In Lasers With Delayed Incoherent Optical Feedback"

            Opt. Commun. 96 (4-6), 259-266 (1993).

 

            ABSTRACT: Dynamic phenomena that incoherent optical feedback induces in single-mode class-B lasers are examined. Numerical simulations reveal the coexistence of sustained periodic relaxation oscillations and regenerative periodic spiking oscillations leading to chaotic oscillations.

 

11.       K. W. Delong, J. Yumoto, and N. Uesugi

            "Frequency-Domain Measurement Of Quantum Beats"

            Phys. Rev. A 48 (1), 702-706 (1993).

 

            ABSTRACT: We use a density-matrix formalism to illustrate the possibilities of detecting quantum-beat phenomena in the frequency domain. In a pump-probe absorption-saturation experiment, the differential-transmission spectrum is shown to have features at frequencies that are separated from the laser frequency by the quantum-beat frequency. We show the conditions under which these features are observable.

 

12.       P. D. Drummond and A. D. Hardman

            "Simulation Of Quantum Effects In Raman-Active Wave-Guides"

            Europhys. Lett. 21 (3), 279-284 (1993).

 

            ABSTRACT: An approximate technique for simulating quantum noise in electromagnetic radiation propagating through a Raman-active Kerr medium is developed. The method is based on a truncated Wigner representation, and is valid at large photon number with a finite frequency cut-off. Results for squeezing in quantum solitons are obtained. We find that at low temperatures Raman scattering does not significantly degrade squeezing.

 

13.       P. D. Drummond, R. M. Shelby, S. R. Friberg, and Y. Yamamoto

            "Quantum Solitons In Optical Fibers"

            Nature 365 (6444), 307-313 (1993).

 

            ABSTRACT: The quantum-mechanical properties of long-lived optical pulses known as solitons have recently been studied theoretically and observed experimentally. These experiments suggest effective ways of reducing quantum noise in signal transmission and of performing quantum-mechanical non-demolition measurements without destroying the signal.

 

14.       S. R. Friberg

            "Demonstration Of Colliding-Soliton All-Optical Switching"

            Appl. Phys. Lett. 63 (4), 429-431 (1993).

 

            ABSTRACT: A colliding-soliton switch that takes advantage of the conservation properties of interacting solitons is demonstrated experimentally. We show that the switch, which can operate as an optical demultiplexer or as a logic gate, responds to incoming signal solitons without altering them. This is a consequence of its quantum nondemolition measurement capabilities, and allows multiple operations to be performed with the same soliton. Operation at rates exceeding 250 Gbit/s should be possible.

 

15.       T. Fujisawa, T. Saku, Y. Hirayama, and S. Tarucha

            "Sub-Mu-M Wide Channels With Surface-Potential Compensated By Focused Si Ion-Beam Implantation"

            Appl. Phys. Lett. 63 (1), 51-53 (1993).

 

            ABSTRACT: We propose and demonstrate a novel technique using focused Si ion beam implantation to produce high-quality mesoscopic channels. Low-energy Si implantation compensates the surface potential of a modulation-doped heterostructure that is designed to have no conductive channels at the heterointerface. The implantation forms a conductive channel separated from the damaged implanted region. The mobility of the channel is improved by decreasing the ion energy from 100 to 35 keV. Sub-mum to 5 mum wide channels fabricated by 35 keV Si+ ions show a mobility of 5.3 x 10(5) cm2/V s and a ballistic length of 3.1 mum at 1.5 K.

 

16.       T. Fukuda and Y. Hirota

            "Scanning-Tunneling-Microscopy Study Of Deoxygenated And Deionized Water Rinsed Gaas(111)-B Surfaces"

            J. Vac. Sci. Technol. B 11 (6), 1982-1986 (1993).

 

            ABSTRACT: GaAs(111)-B (arsenic terminated) surfaces prepared by rinsing with running deoxygenated and de-ionized water (DODIW) were investigated by scanning tunneling microscopy in ultrahigh vacuum. After annealing the sample, As-rich 2 X 2 reconstruction was found between 415 and 500-degrees-C. Above 500-degrees-C, Ga-rich square-root 19 X square-root 19-like structures were also found around As desorbed triangular valleys. Although details of the reconstructions were slightly different from molecular-beam epitaxially grown surfaces, similar temperature dependence proved that DODIW-treated surfaces were effectively passivated against oxidation.

 

17.       T. Furubayashi, K. Kinoshita, T. Yamada, and T. Matsumoto

            "Mossbauer Studies Of Superconducting La2-Xca1+Xcu2o6 Doped With Fe-57"

            Physica C 204 (3-4), 315-321 (1993).

 

            ABSTRACT: Mossbauer spectroscopy and magnetization measurements were employed to study the superconducting oxide (La2-xCa1+x(Cu1-yFey)2O6)-Fe-57 (x=0.18,y=0.01) prepared under oxygen pressures of 2 atm (non-superconducting), 50 atm (T(c)=9 K) and 400 atm (T(c)=43 K). In addition to powder samples, samples with aligned crystal direction were used in a Mossbauer study for evaluating the direction and the sign of the electric field gradient. From the paramagnetic spectra at room temperature, it was concluded that, in the superconducting samples, a larger part of the Fe atoms in Cu sites have an excess oxygen neighbor between two CuO2 planes compared to the non-superconducting sample. The excess oxygen possibly induces superconductivity by increasing holes doped in the CuO2 plane. The measurements at low temperatures showed that the samples prepared in 2 and 50 atm O2 are magnetically ordered with a transition temperature of about 15 K, consistent with the results of magnetization measurements. In contrast, the magnetic ordering was largely suppressed even at 4.2 K in the superconducting sample prepared in 400 atm O2.

 

18.       N. Hatakenaka

            "Interaction Time Of Korteweg-Devries Solitons"

            Phys. Rev. E 48 (5), 4033-4036 (1993).

 

            ABSTRACT: The interaction time of Korteweg-de Vries solitons is studied by using Konno and Ito's complex-time-plane method [J. Phys. Soc. Jpn. 56, 987 (1987)]. We find that the behavior of the interaction time reflects the particle-wave dual nature of the soliton. Most of this feature is explained by the rectangular model of Aossey et al. [Phys. Rev. A 45, 2606 (1992)].

 

19.       H. Heitmann, Y. Kadota, T. Kawakami, and Y. Yamamoto

            "Single Transverse-Mode Microcavity Laser With Ultralow Threshold"

            Jpn. J. Appl. Phys. Part 2 - Lett. 32 (8B), L1141-L1143 (1993).

 

            ABSTRACT: We report on experiments with surface emitting microcavity semiconductor lasers with a mesa-like three-dimensional structure. Mode selectivity is introduced by the small diameter of the top mirror, making single transverse mode oscillation possible. This leads to a reduced threshold pump power as compared with a planar sample with the same structure- on optical pumping we observed a threshold power of about 7 muW at 4 K. The observed laser threshold and spontaneous emission coefficient were compared with the theoretical prediction, giving a reasonable agreement.

 

20.       H. Hibino, T. Fukuda, M. Suzuki, Y. Homma, T. Sato, M. Iwatsuki, K. Miki, and H. Tokumoto

            "High-Temperature Scanning-Tunneling-Microscopy Observation Of Phase-Transitions And Reconstruction On A Vicinal Si(111) Surface"

            Phys. Rev. B 47 (19), 13027-13030 (1993).

 

            ABSTRACT: The step structure of a vicinal Si(111) surface misoriented 10-degrees to [112BAR] is studied using high-temperature scanning tunneling microscopy (STM). Phase transitions on the vicinal Si(111) surface are observed in real time on an atomic scale. During cooling from above the (1 X 1)-to-(7 X 7) transition temperature, slender (111) facets with a 7 X 7 structure appear, and these facets widen as the temperature decreases. At the initial stage of step bunching, no surface reconstruction is observed on the step bunch. Below 700-degrees-C, however, nucleation of reconstructed (331) facets starts on the step bunch. These STM results are compared with our previous reflection high-energy electron-diffraction results

 

21.       H. Hibino, N. Shimizu, and Y. Shinoda

            "Mesh Pattern Of Ge Islands Grown Using Solid-Phase Epitaxy"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 11 (5), 2458-2462 (1993).

 

            ABSTRACT: We present mesh patterns of Ge islands grown on a Si (111) surface using solid phase epitaxy. Typical experimental conditions for the formation of these mesh patterns are substrate temperatures of 300-500-degrees-C and a Ge thickness of about 10 angstrom. The mesh pattern is due to preferential crystallization of a-Ge films at steps and at out-of-phase boundaries of 7 X 7 structures.

 

22.       Y. Hirayama and S. Tarucha

            "High-Temperature Ballistic Transport Observed In Algaas/Ingaas/Gaas Small 4-Terminal Structures"

            Appl. Phys. Lett. 63 (17), 2366-2368 (1993).

 

            ABSTRACT: Four-terminal structures are fabricated by focused-ion-beam (FIB) scanning on an AlGaAs/InGaAs/GaAs modulation doped structure. The large carrier density of this system results in small depletion spreading and a 260-nm-square four-terminal structure is successfully formed. The bend resistance of this structure indicates that ballistic coupling between two facing terminals remains up to room temperature. Thermal broadening of electron energy enhances the ballistic nature of the system at high temperature.

 

23.       Y. Hirayama, Y. Tokura, A. D. Wieck, S. Koch, R. J. Haug, K. Vonklitzing, and K. Ploog

            "Transport Characteristics Of A Window-Coupled In-Plane-Gated Wire System"

            Phys. Rev. B 48 (11), 7991-7998 (1993).

 

            ABSTRACT: Low-temperature (T almost-equal-to 50 mK) transport characteristics are measured for parallel wires coupled by a ballistic window. The structure is fabricated by focused Ga ion-beam scanning and subsequent annealing. The size of the structure is modified by in-plane-gated operation. At zero magnetic field, the transport characteristics are governed by the mode matching between one-dimensional modes in the wires and quasi-zero-dimensional modes in the window. When four-terminal resistance is measured as a function of in-plane-gate voltage, a small period oscillation is superimposed on the background oscillation corresponding to the subband population in each wire. At intermediate magnetic fields, Aharonov-Bohm interference effects are observed in both the magnetic field and the in-plane-gate voltage dependence. These originate from the circulating channel in the window. Theoretical calculations essentially reproduce the experimental results, supporting these explanations.

 

24.       Y. Hirota

            "Schottky Characteristics Of Gaas Surface Cleaned By Ultrasonic Running Deionized Water-Treatment"

            Appl. Phys. Lett. 63 (14), 1936-1938 (1993).

 

            ABSTRACT: Schottky characteristics for n-type (001)-GaAs surfaces prepared by ultrasonic running deionized water treatment (URDIW) are investigated by measuring Schottky diodes. Schottky barrier height for the URDIW treated surfaces is more sensitive to the metal work function, and is smaller compared to those of the chemically etched surfaces. We discuss Schottky characteristics for the URDIW treated surfaces based on the hydrogen-terminated model.

 

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

            "Apfim Studies Of Compositional Inhomogeneity In Sputtered Co-Cr Thin-Films"

            IEEE Trans. Magn. 29 (6), 3745-3747 (1993).

 

            ABSTRACT: Atom probe analysis results of Co-22at%CR bulk alloy and its thin films are presented. While no compositional inhomogeneity is detected from the bulk sample, a significant compositional fluctuation is present in the thin film specimen which is sputter deposited on a heated substrate. The concentration of the Cr enriched region is in the range of 30 - 40 at.%Cr, while that of the Cr depleted region is approximately 5 at.%Cr. Such compositional fluctuations are present within a grain. These results are in agreement with NMR and TEM results.

 

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

            "Atom-Probe Analysis Of Sputtered Co-Cr Magnetic Thin-Films"

            Appl. Surf. Sci. 67 (1-4), 386-390 (1993).

 

            ABSTRACT: Both Co-22at%Cr bulk alloy and its thin films were analyzed by an atom probe field ion microscope. While no compositional inhomogeneity was found in the bulk sample, a significant compositional fluctuation was found in the Co-Cr thin film sample which was deposited on a tungsten tip surface at 200-degrees-C. 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.

 

27.       Y. Horikoshi

            "Migration-Enhanced Epitaxy Of Gaas And Algaas"

            Semicond. Sci. Technol. 8 (6), 1032-1051 (1993).

 

            ABSTRACT: The principle and characteristics of migration-enhanced epitaxy are reviewed. Migration of surface adatoms along the surface is very important for growing high quality layers and atomically flat heterojunctions. In the migration-enhanced epitaxy of GaAs and AlGaAs, migration of surface Ga and Al atoms is enhanced even at low substrate temperatures by evaporating them onto a clean GaAs surface under an As-free or low As pressure atmosphere. Thus, high quality GaAs and AlGaAs layers and flat heterojunctions have been grown by this method. Migration-enhanced epitaxy has also proved useful in investigating atomic processes during epitaxial growth.

 

28.       Y. Horikoshi

            "Surface Processes In Migration-Enhanced Epitaxy Of Iii-V Compound Semiconductors"

            Appl. Surf. Sci. 65-6, 560-568 (1993).

 

            ABSTRACT: Migration-enhanced epitaxy (MEE) of III-V compound semiconductors, which is based on alternately supplying Group III and Group V sources, is useful for growing high-quality epitaxial layers and atomically flat heterojunction interfaces even at very low substrate temperatures and for investigating atomic processes during epitaxial growth. RHEED observation during growth of GaAs revealed that the migration distance of Ga atoms was considerably enhanced by MEE. The effect of MEE is much more pronounced in growth at low substrate temperatures, but MEE using a supplementary As beam was also useful at high temperatures.

 

29.       T. Imada, R. Hari, N. Loveless, L. McEvoy, and M. Sams

            "Determinants Of The Auditory Mismatch Response"

            Electroencephalogr. Clin. Neurophysiol. 87 (3), 144-153 (1993).

 

            ABSTRACT: The auditory mismatch field (MMF) is supposed to reflect a comparison process between an infrequent deviant stimulus and the memory trace left by frequent standard stimuli. Therefore, the MMF amplitude has been thought to depend on the strength of such a trace. We examined this hypothesis in records with a 24-channel planar SQUID magnetometer by varying the number of stimuli preceding each deviant, the interdeviant interval (IDI) and the interstimulus interval (ISI) just preceding the deviant (pISI). When a constant IDI was employed and the number of standards between two deviants varied in different sessions, MMF amplitude increased as the number of standards increased. However, MMF did not depend on the number of standards between two deviants when the number varied within a single session and ISI varied as well. MMF decreased slightly when pISI increased from 0.6 to 3.4 sec. When IDI increased and the ISI remained constant, MMF amplitude increased. Most results can be explained within the framework of the memory-trace hypothesis of MMF generation. However, the strengthening of the trace seems to be a complex process which is also affected by the temporal features of the stimulus sequence.

 

30.       A. Imamoglu and Y. Yamamoto

            "Quantum State Control In Semiconductor Pn Junctions.3. Coulomb Blockade Of Resonant-Tunneling In Pn Microjunctions"

            Int. J. Mod. Phys. B 7 (11), 2065-2083 (1993).

 

            ABSTRACT: We show that Coulomb blockade of resonant tunneling in semiconductor heterojunctions creates correlations between single-charge tunneling and single-photon emission events. The single electron (hole) charging energy has to exceed the characteristic energy of the thermal fluctuations, for these correlations to be observable. The light field generated by the analyzed mesoscopic heterostructure is inherently nonclassical. The effects of quantum confinement and possible applications of the single-electron/single-photon manipulation techniques are discussed.

 

31.       A. Imamoglu and Y. Yamamoto

            "Noise Suppression In Semiconductor P-I-N Junctions - Transition From Macroscopic Squeezing To Mesoscopic Coulomb Blockade Of Electron-Emission Processes"

            Phys. Rev. Lett. 70 (21), 3327-3330 (1993).

 

            ABSTRACT: We analyze noise suppression properties of a constant-current driven p-i-n heterojunction. It is shown that the junction capacitance and temperature determine the minimum measurement time required for obtaining sub-Poissonian electron injection. As the capacitance of the junction is reduced, the noise spectrum develops a ''regulated single electron emission peak'' at the single electron charging frequency, indicating regulation of the individual thermionic emission events and therefore a transition from macroscopic squeezing to Coulomb blockade regime.

 

32.       S. Inoue, S. Machida, and Y. Yamamoto

            "Squeezing In An Injection-Locked Semiconductor-Laser"

            Phys. Rev. A 48 (3), 2230-2234 (1993).

 

            ABSTRACT: The intensity-noise properties of an injection-locked semiconductor laser were studied experimentally. The constant-current-driven semiconductor laser producing the amplitude-squeezed state whose intensity noise was reduced below the standard quantum limit (SQL) by 0.72 dB was injection-locked by an external master laser. The measured intensity-noise level of the injection-locked semiconductor laser was 0.91 dB below the SQL. This experimental result indicates that a phase-coherent amplitude-squeezed state or squeezed vacuum state together with a reference local oscillator wave can be generated directly by semiconductor laser systems.

 

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

            "Phase-To-Amplitude Conversion Noise In Squeezed-Vacuum-State Generation From A Semiconductor-Laser"

            J. Opt. Soc. Am. B-Opt. Phys. 10 (11), 2121-2129 (1993).

 

            ABSTRACT: An excess phase-to-amplitude conversion noise was observed in the interferometric cancellation for the coherent excitation of the squeezed output from an injection-locked laser. We show theoretically that this phase-to-amplitude conversion noise can be eliminated and that it is possible to generate squeezed vacuum states by the use of a semiconductor laser system.

 

34.       T. Irino and H. Kawahara

            "Signal Reconstruction From Modified Auditory Wavelet Transform"

            IEEE Trans. Signal Process. 41 (12), 3549-3554 (1993).

 

            ABSTRACT: We propose a new method for signal modification in auditory peripheral representation: an auditory wavelet transform and algorithms for reconstructing a signal from a modified wavelet transform. We present the characteristics of signal analysis, synthesis, and reconstruction and also the data reduction criteria for signal modification.

 

35.       T. Ito, T. Ohno, K. Shiraishi, and E. Yamaguchi

            "Computer-Aided Materials Design For Semiconductors"

            Adv. Mater. 5 (3), 198-206 (1993).

 

            ABSTRACT: Computer-aided materials design for semiconductors is reviewed. Reliable predictions are possible for a wide range of problems, such as the behavior of various heterovalent atomic species in III-V semiconductors, including C (conduction type), Si (DX-center), Ge (GaAs/Ge superlattices), S, Se and Te (passivation of GaAs surfaces), by using such computer-aided calculation techniques as pseudopotential methods.

 

36.       J. R. Jeffers, N. Imoto, and R. Loudon

            "Quantum Optics Of Traveling-Wave Attenuators And Amplifiers"

            Phys. Rev. A 47 (4), 3346-3359 (1993).

 

            ABSTRACT: We use a continuous-mode quantization scheme to derive relations between the output- and input-field operators for traveling-wave propagation along attenuating and amplifying optical fibers. These relations provide complete information on the temporal and longitudinal spatial developments of the signal field. They are used here to obtain the effects of propagation on the first and second moments of the photocount in direct detection and of the signal field measured in balanced homodyne detection. Some of the results are similar to those obtained for attenuation or amplification of standing waves in cavities, and, for example, the survival of any input squeezing still limits the maximum gain to twofold. There are, however, additional propagation effects for the traveling-wave system. Thus, in direct detection, it is necessary to take account of the changes in gain profile with propagation distance, and in homodyne detection there are fundamental quantum-mechanical restrictions on the minimum field uncertainties that can be achieved in measurements at separated space-time points. These uncertainty properties are derived in detail and illustrated by the example of a squeezed input signal.

 

37.       Y. Jimbo, H. P. C. Robinson, and A. Kawana

            "Simultaneous Measurement Of Intracellular Calcium And Electrical-Activity From Patterned Neural Networks In Culture"

            IEEE Trans. Biomed. Eng. 40 (8), 804-810 (1993).

 

            ABSTRACT: Multisite extracellular electrical activity and intracellular calcium were recorded simultaneously. Electrical sig. nals were measured using microelectrode array substrates. A novel cell positioning technique was combined with a method for controlling neurite outgrowth, which allowed cell-electrode contacts to be established easily, thus facilitating the electrical recording. Intracellular calcium was measured optically using the indicator fluo 3. Under low-magnesium conditions, cultured rat cortical neurons showed periodic transients of fluo-3 fluorescence, which were synchronized with the periodic bursting observed electrically. The intervals between bursts could be determined by electrical stimulation through the substrate electrodes. The results suggest that functional synaptic connections are formed in the culture system.

 

38.       N. Jourdan, H. Yamaguchi, and Y. Horikoshi

            "Dependence Of Eras Clustering And Er Segregation In Eras/Gaas Heterostructures On Growth Temperature"

            Jpn. J. Appl. Phys. Part 2 - Lett. 32 (12B), L1784-L1787 (1993).

 

            ABSTRACT: The effect of growth temperature on the growth properties of ErAs/GaAs heterostructures grown by low-temperature migration-enhanced epitaxy and molecular beam epitaxy is investigated in detail using transmission electron microscopy, double-crystal X-ray diffraction and secondary ion mass spectroscopy. Our results demonstrate that the formation of ErAs clusters at the ErAs/GaAs interface occurs even at very low growth temperatures (320-degrees-C). Moreover, we clearly observe that the size of the clusters drastically increases and Er segregation takes place when the growth temperature is increased. All our characterization results suggest that when the samples are grown by migration-enhanced epitaxy at 320-degrees-C, these problems can be limited, leading to an enhancement of crystal quality.

 

39.       Y. Kanemitsu, T. Ogawa, K. Shiraishi, and K. Takeda

            "Visible Photoluminescence From Oxidized Si Nanometer-Sized Spheres - Exciton Confinement On A Spherical-Shell"

            Phys. Rev. B 48 (7), 4883-4886 (1993).

 

            ABSTRACT: We report strong visible photoluminescence (PL) at room temperature from oxidized Si nanometer-sized spheres with a spherical crystalline Si (c-Si) core and an amorphous SiO2 (a-SiO2) surface layer. The peak energy of the broad PL spectrum is about 1.65 eV, which is independent of the core diameter. We propose a model in which excitons are confined on a spherical shell, an interfacial layer between the c-Si core and the a-SiO2 surface layer, and in which the exciton confinement enhances the oscillator strength and the PL intensity.

 

40.       M. Kasu and N. Kobayashi

            "Equilibrium Multiatomic Step Structure Of Gaas(001) Vicinal Surfaces Grown By Metalorganic Chemical Vapor-Deposition"

            Appl. Phys. Lett. 62 (11), 1262-1264 (1993).

 

            ABSTRACT: We have studied, in the equilibrium state, the multiatomic step (multistep) structure only a few nanometers high on GaAs(001) vicinal surfaces grown by metalorganic chemical vapor deposition (MOCVD). Annealing (growth interruption) straightens multistep edges, but even after the annealing the multistep on the [110BAR]-misoriented surface is straighter than the multistep on the [110]-misoriented surface. This indicates that the free energy of the [110BAR]-step is lower than that of the [110]-step. Step bunching on this vicinal surface is caused by the formation of two facets with different orientations.

 

41.       M. Kasu, N. Kobayashi, and H. Yamaguchi

            "Scanning-Tunneling-Microscopy Observation Of Monolayer Steps On Gaas(001) Vicinal Surfaces Grown By Metalorganic Chemical-Vapor-Deposition"

            Appl. Phys. Lett. 63 (5), 678-680 (1993).

 

            ABSTRACT: Using scanning tunneling microscopy (STM), we have observed monolayer steps for the first time on (001) GaAs vicinal surfaces grown by metalorganic chemical vapor deposition (MOCVD). The surface was passivated with As to protect it from air during the transfer from the MOCVD to the STM. We found that the monolayer step edges on the surface misoriented in the [110] direction undulate with about 2 times larger amplitude than the surface misoriented in the [110BAR] direction.

 

42.       K. Kinoshita and T. Yamada

            "Superconducting Properties Of 2126 Compounds La2-Xca1+Xcu2o6 (0.08-Less-Than-Or-Equal-To-X-Less-Than-Or-Equal-To-0.25)"

            Phase Transit. 41 (1-4), 143-148 (1993).

 

            ABSTRACT: Superconducting properties of La2-xCa1+xCu2O6 (0.08 less than or equal to x less than or equal to 0.25) as functions of composition (x) and oxygen pressure during synthesis (P-O2, up to 400 atm) were investigated through measurements of electrical resistivity and magnetic susceptibility. The highest T-c(onset) and T-c(zero) were obtained at the solubility limit of Ca for La (x = 0.25) under P-O2 of 400 atm, which were about 60 K and 51 K, respectively. Three-dimensional (3D) antiferromagnetic order was observed in nonsuperconducting and weakly superconducting La2-xCa1+xCu2O6+/-delta.

 

43.       M. Kitagawa and M. Ueda

            "Squeezed Spin States"

            Phys. Rev. A 47 (6), 5138-5143 (1993).

 

            ABSTRACT: The basic concept of squeezed spin states is established and the principles for their generation are discussed. Two proposed mechanisms, referred to as one-axis twisting and two-axis countertwisting, are shown to reduce the standard quantum noise S/2 of the coherent S-spin state down to 1/2(S/3)1/3 and 1/2, respectively. Implementations of spin squeezing in interferometers are also discussed.

 

44.       N. Kobayashi and Y. Kobayashi

            "Insitu Monitoring And Control Of Atomic Layer Epitaxy By Surface Photoabsorption"

            Thin Solid Films 225 (1-2), 32-39 (1993).

 

            ABSTRACT: Surface photo-absorption (SPA) is a real-time optical probe for examining growth and gives us a microscopic insight into atomic processes occurring on a growth surface. SPA observations during GaAs and InP atomic layer epitaxy (ALE) using trimethyl Group III sources and Group V hydrides demonstrate that the adsorption of trimethyl source saturates during the trimethyl source supply period and that the saturated surface corresponds to a metastably methyl-terminated surface with a lifetime of several tens of seconds. In contrast, when the trimethyl source is supplied onto the Group III metal surface, an increase in the SPA reflectivity from the metal surface level is observed, indicating that the trimethyl source molecule decomposes on the Group III metal surface via adsorption. These observations give rise to the conclusion that the growth rate self-limitation in ALE is caused by the inhibited adsorption of excessively supplied Group III source molecules on the methyl-terminated surface, and not by a selective adsorption mechanism. SPA observation also makes it possible to determine readily and precisely the growth parameters for ALE which strongly depend on the reactor design and the gas flow condition.

 

45.       M. Kondo, K. Morigaki, K. Takeda, K. Shiraishi, and M. Fujiki

            "Photocreated Metastable State In Organopolysilanes"

            J. Non-Cryst. Solids 166, 1267-1270 (1993).

 

            ABSTRACT: A photocreated metastable state in organopolysilanes has been studied using the electron spin resonance technique. Depending on the excitation photon energy, two different kinds of signals have been observed for the first time. The origin of the signals are discussed, in comparison with a first principles calculation. As a result, the self-trapping of an electron and the sodium related defect creation are suggested in organopolysilane depending on the excitation energy. These results are compared with the Staebler-Wronski effect in a-Si:H.

 

46.       J. C. Lodder, H. Vankranenburg, K. Takei, and Y. Maeda

            "Nmr Measurements On Obliquely Evaporated Co-Cr Films"

            J. Magn. Magn. Mater. 118 (1-2), 248-262 (1993).

 

            ABSTRACT: The distribution of the hyperfine fields or the resonance frequencies in metals and alloys obtained by NMR measurements have been known for a long time. Recently, new experimental data have been published about thin films for studying their chemical inhomogeneities. An example is the study on sputtered and evaporated Co-Cr layers. In this paper we report on the compositional distribution of co-evaporated Co-Cr films by using the Co spin-echo NMR technique. For comparison single source evaporated samples of Co-Cr and pure Co as well as two alloyed ribbons (''bulk'' samples) have also been measured. Based on the NMR results the local Cr concentration of the ferromagnetic and less ferromagnetic regions are determined. In comparison the data from the co-evaporated films, even at low substrate temperature, have clearly shown the presence of a process-induced compositional separation. This is in qualitative agreement with the magnetic properties of the samples.

 

47.       N. Maeda, M. Kawashima, and Y. Horikoshi

            "Epitaxial-Growth Of Al Films On Modified Alas(001) Surfaces"

            J. Appl. Phys. 74 (7), 4461-4471 (1993).

 

            ABSTRACT: In order to understand the physical principles which underlie the formation of metal/semiconductor interfaces, epitaxial Al films are grown by molecular beam epitaxy on As-stabilized and Al-stabilized AlAs(001) surfaces some of which were coated with a single monolayer (1 ML) of Ga or In. Reflection high-energy electron diffraction and x-ray diffraction measurements reveal that the growth direction and epitaxial relationship of the Al films are drastically changed by the surface modification by 1 ML Ga or In. A variety of Al film configurations are obtained, of which the Al(001)/Ga(or In)/AlAs(001) heterostructure is technologically important because it has an ideally lattice matched metal/semiconductor heterostructure. We propose structural models for three Al phases, i.e., Al(001) and two kinds of Al(110), and discuss the physical origin of the variation of Al phases. It is shown that the changes observed in the epitaxial relationships of Al films can be systematically explained in terms of bond strengths at the interface. In the growth of metals on semiconductors, interface modification is shown to be effective for controlling the growth.

 

48.       Y. Maeda

            "Compositional Separation In Co-Cr Based Alloy-Films"

            Adv. Mater. 5 (3), 210-211 (1993).

 

            ABSTRACT: Co-Cr based alloy thin films are being studied extensively for applications as high-density magnetic recording media. The observation of a compositional microstructure, the ''chrysanthemum-like pattern'' (CP) in the Figure, is the first step towards understanding the mechanisms that make such applications possible. Much work remains to be done on the origin of the compositional separation causing the CP and on methods of controlling the CP.

 

49.       Y. Maeda, K. Takei, and D. J. Rogers

            "Detection Of Compositional Separation In Co-Ru Alloy Magnetic-Films"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 32 (10), 4540-4541 (1993).

 

            ABSTRACT: We examined the possible occurrence of compositional separation (CS) in hcp Co-Ru alloy magnetic films. Using spin echo Co-58 NMR and transmisson electron microscopy, we found that CS, which produces a Co-rich component (almost-equal-to 10 at.% Ru), occurs in sputtered Co- almost-equal-to 33 at % Ru-films when substrate temperature is elevated to 400-degrees-C. The results suggest that the origin of CS lies in magnetically induced phase separation during film growth.

 

50.       T. Makimoto and N. Kobayashi

            "Carbon Atomic Layer Doping In Algaas By Metalorganic Chemical-Vapor-Deposition And Its Application To A P-Type Modulation-Doped Structure"

            Jpn. J. Appl. Phys. Part 2 - Lett. 32 (9B), L1300-L1303 (1993).

 

            ABSTRACT: Carbon (C) atomic layer doping in AlGaAs is demonstrated. During undoped AlGaAs growth by conventional low-pressure metalorganic chemical vapor deposition, C atomic layer doping is performed by supplying trimethyl-gallium onto AlGaAs surfaces under arsine-free conditions. C incorporation increases with increasing Al composition of the surface layer onto which trimethylgallium is supplied, suggesting that the C incorporation mechanism is that As atoms of the AlGaAs surface are partially replaced by C atoms of methyl groups to become acceptors. The capacitance-voltage measurement of the C atomic layer doped AlGaAs shows a carrier profile with a full width at half-maximum as narrow as 8.0 nm at a peak carrier concentration of 2.1 x 10(18) cm-3, indicating that the diffusion of C atoms in AlGaAs is not serious during growth at 610-degrees-C. A p-type modulation doped AlGaAs/GaAs structure was fabricated using C atomic layer doping, and a mobility of 1. 3 x 10(5) cm2/V - s was obtained at 1.5 K for a sheet hole density of 3.9 x 10(11) cm-2. Because of the high quality two-dimensional hole gas, a region limited by acoustic phonon scattering can be seen in the temperature dependence of hole mobility.

 

51.       T. Makimoto and N. Kobayashi

            "High 2-Dimensional Electron-Mobility In Si Atomic-Layer Doped N-Algaas Gaas Grown By Metalorganic Chemical-Vapor Deposition"

            Jpn. J. Appl. Phys. Part 2 - Lett. 32 (5A), L648-L649 (1993).

 

            ABSTRACT: Si atomic-layer doped n-AlGaAs/GaAs structures have been grown by metalorganic chemical vapor deposition using triethyl sources, arsine and silane. Two dimensional electron mobility of 1.3 x 10(6) cm2/V.s is obtained at 4.2 K for a sheet electron concentration of 4.8 x 10(11) cm-2. Because of the high quality of the two-dimensional electron gas, acoustic phonon scattering can be seen in the temperature dependence.

 

52.       P. Mandel, C. Etrich, and K. Otsuka

            "Laser Rate-Equations With Phase-Sensitive Interactions"

            IEEE J. Quantum Electron. 29 (3), 836-843 (1993).

 

            ABSTRACT: We derive a set of multimode rate equations which couple the complex fields to the mean number of amplifiers. We show that in the case of semiconductor lasers, phase-sensitive interactions must be retained. The resulting equations are studied and bifurcation diagrams are presented that display the steady, periodic, and quasiperiodic solutions.

 

53.       P. Mandel, M. Georgiou, K. Otsuka, and D. Pieroux

            "Transient And Modulation Dynamics Of A Multimode Fabry-Perot Laser"

            Opt. Commun. 100 (1-4), 341-350 (1993).

 

            ABSTRACT: The two-mode rate equations for a laser in a Fabry-Perot cavity are studied, taking into account the dynamics of spatial hole-burning. We prove analytically that each mode intensity has a transient behavior characterized by two damped oscillation frequencies, while the total intensity displays a domain where only the largest oscillation frequency remains; this domain appears to display antiphase dynamics. These results are generalized to N lasing modes. We then analyze the response of the two-mode laser to a periodic pump modulation. For small modulation depth, the two oscillation frequencies are clearly displayed as resonances on the response curve. For deeper modulation depth, the beating of the modulation frequency and the largest internal oscillation frequency produces a subharmonic sequence to chaos. This chaotic domain disappears in a crisis when it collides with the branch of stable periodic oscillations associated with the smaller oscillation frequency which coexists with the subharmonic cascade.

 

54.       F. M. Matinaga, A. Karlsson, S. Machida, Y. Yamamoto, T. Suzuki, Y. Kadota, and M. Keda

            "Low-Threshold Operation Of Hemispherical Microcavity Single-Quantum-Well Lasers At 4-K"

            Appl. Phys. Lett. 62 (5), 443-445 (1993).

 

            ABSTRACT: We demonstrate low-threshold lasing at 4 K in optically pumped hemispherical In0.2Ga0.8As single-quantum-well microcavities. The incident threshold pump power density is 11 kW/cm2 corresponding to an absorbed power density of about 320 W/cm2, and the measured spontaneous emission factor beta is about 0.01.

 

55.       Y. Matsuoka, K. Kurishima, and T. Makimoto

            "High-Frequency Inp/Ingaas Double-Heterojunction Bipolar-Transistors On A Si Substrate"

            IEEE Electron Device Lett. 14 (7), 357-359 (1993).

 

            ABSTRACT: Self-aligned high-frequency InP/InGaAs double heterojunction bipolar transistors (DHBT's) have been fabricated on a Si substrate for the first time. A current gain of 40 was obtained for a DHBT with an emitter dimension of 1.6 x 19 mum2. The S parameters were measured for various bias points. In the case of I(C) = 15 mA, f(T) was 59 GHz at V(CE) = 1.8 V, and f(max) was 69 GHz at V(CE) = 2.3 V. Due to the InP collector, breakdown voltage was so high that a high V(CE) of 3.8 V was applied for I(C) = 7.5 mA in the S-parameter measurements to give an f(T) of 39 GHz and an f(max) of 52 GHz.

 

56.       N. Mitani and S. Kurihara

            "Superconductivity Coupled To Density Waves"

            Phys. Rev. B 48 (5), 3356-3367 (1993).

 

            ABSTRACT: We investigate a mechanism of superconductivity on the basis of the nested-Fermi-liquid theory. A set of parquet equations is derived to investigate the instability towards superconductivity and spin- or charge-density-wave states. The phase diagram is examined on the basis of the parquet equations. We find that the polarization mode of the marginal-Fermi-liquid-type is of vital importance to superconductivity. We also discuss the properties of a superconductor on the basis of the nested Fermi liquid.

 

57.       N. Mitani and S. Kurihara

            "Radiative-Corrections To Spin-Waves In The Interacting Hole-Spin Model"

            Physica C 206 (1-2), 13-21 (1993).

 

            ABSTRACT: We investigate the quantum fluctuation effect of the two-dimensional Heisenberg antiferromagnet coupled to conduction holes via a Kondo-type exchange interaction. By the use of the large-S expansion, we find that the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction around the momentum transfer Q of antiferromagnetic (AFM) fluctuations has the crucial effect of ''melting'' the AFM long-range order. We obtain a qualitative phase boundary as a function of temperature and hole doping. We examine analytically the effects of the renormalized spin waves on the superconducting phase. We show the effects of quantum spin fluctuations on the superconducting phase boundary and the NMR spin relaxation rate.

 

58.       M. Mitsunaga, N. Uesugi, and K. Sugiyama

            "Kilohertz-Resolution Pump-Probe Spectroscopy In Pr3+Yalo3"

            Opt. Lett. 18 (15), 1256-1258 (1993).

 

            ABSTRACT: We observed saturated absorption spectra of hole widths as narrow as 10.5 kHz with an excellent signal-to-noise ratio in a cryogenic Pr3+:YAlO3 sample, using a frequency-stabilized dye laser in a noncollinear frequency-domain pump-probe measurement. More-detailed theoretical and experimental analyses revealed the existence of an ultranarrow peak of width 10 Hz at the center of the line shape that could be attributed to grating diffraction of the pump beam.

 

59.       N. Nagaosa and T. Ogawa

            "Electron-Hole System In One-Dimension"

            Solid State Commun. 88 (4), 295-299 (1993).

 

            ABSTRACT: A high-density electron-hole system in one dimension is studied theoretically. Competition between the exciton Bose condensation and other Fermi-surface instabilities is clarified within a framework of the two-band g-ology. There is a parameter region where unconventional interband Cooper pairing with nonzero total momentum occurs. Optical spectra yield the Fermi-edge singularity resulting from the exciton condensation. Effects of backward scattering and random potential are also discussed.

 

60.       I. Nagata, A. Kawana, and N. Nakatsuji

            "Perpendicular Contact Guidance Of Cns Neuroblasts On Artificial Microstructures"

            Development 117 (1), 401-408 (1993).

 

            ABSTRACT: Rodent CNS neuroblasts show parallel and perpendicular contact guidance behaviors on aligned neurite bundles in microexplant cultures (Nakatsuji, N. and Nagata, I. (1989) Development, 106, 441-447; N. I. and N. N. (1991) ibid., 112, 581-590). To test the hypothesis that the physical surface structure of the neurite bundle causes the perpendicular contact guidance, we cultured dissociated neuroblasts on quartz plates on which grating-like microstructures were fabricated by lithographic techniques. Various types of CNS neuroblasts, but not PNS neurons, oriented their processes and migrated both perpendicular and parallel to the axis of the microstructure. Perpendicular orientation was frequently observed when the microstructured grooves had depths between 0.3 mum and 0.8 mum and a width of 1 mum, which roughly mimics a tightly aligned neurite bundle. Thus, CNS neuroblasts have the ability to extend their processes and migrate perpendicular to aligned surface microstructures.

 

61.       J. Nakamura, H. Ban, M. Morita, and A. Tanaka

            "Pattern Fabrication Of Chemically Amplified Resist On An Interdigitated Array Electrode"

            Jpn. J. Appl. Phys. Part 2 - Lett. 32 (6A), L813-L815 (1993).

 

            ABSTRACT: The patterning of the chemically amplified resist SAL601 on an interdigitated array electrode (IDA) has been carried out. When direct current is applied to resist films during the post-exposure baking process, the resist sensitivity is low near the edge of the cathode on the IDA and there is a semicircular cavity in a cross-sectional-developed pattern. It is considered that catalytic protons generated during exposure reduce, becoming electrically neutral on the cathode surface and losing their catalytic ability f or crosslinking reactions. From the size of the cavity, the acid diffusion coefficient can be roughly estimated to be 70 nm2/s.

 

62.       H. Nakano and H. Takayanagi

            "Quasi-Particle Interferometer Controlled By Quantum-Correlated Andreev Reflection"

            Phys. Rev. B 47 (13), 7986-7994 (1993).

 

            ABSTRACT: We propose a quasiparticle interferometer and give a theoretical analysis for it. It consists of a Josephson junction (JJ) and a Y junction composed of normal-electron waveguides. The interferometer should enable us to confirm experimentally the phase interaction between a quasiparticle and a super-conducting state at the superconductor-normal-metal (SN) interface. This interaction is caused by Andreev reflection. The supercurrent through the JJ modifies, by Andreev reflection, the interference of a quasiparticle in the waveguide and affects the normal resistance of the waveguide. The dependence of the resistance on the phase difference of JJ is determined by the characteristics of the Y junction and the normal reflection at the SN interface.

 

63.       S. Nakata

            "Observation Of Coulomb-Blockade Oscillations By The Back Gate With Subattofarad Mutual Capacitance"

            Phys. Rev. B 47 (3), 1679-1682 (1993).

 

            ABSTRACT: A quantum dot is formed in AlxGa1-xAs/GaAs using the split-gate method. First the characteristics of the point contact, which determine the electron transport in the quantum dot, are investigated. Quantized conductance peculiar to the one-dimensional subband is observed. Next the transport properties of the quantum dot are studied by changing the voltage of the back gate, which is placed about 360 mum from the dot. Coulomb-blockade oscillations are observed before the current is completely pinched off. The charging energy of the dot is estimated to be about 0.6 meV based on the temperature dependence and source-drain voltage dependence of the oscillations. It is clarified experimentally that only the mutual capacitance between the back gate and the dot determines the oscillation period.

 

64.       H. Nejoh, M. Ueda, and M. Aono

            "Single-Electron-Charging Effect Controlled By The Distance Between A Substrate And A Liquid-Crystal Molecule"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 32 (3B), 1480-1483 (1993).

 

            ABSTRACT: Single-electron-charging effects in a minuscule liquid-crystal molecule cannot be described in terms of a single-parameter-the capacitance. We performed a molecular-orbital-calculation to explain unequal Coulomb-staircase-edge spacings observed at room temperature. Since Coulomb blockade is a phenomenon associated with electron tunneling, it is describable using a transition probability from the initial state to the final state, where the initial state is the state before an electron enters into a molecule and the final state is the state after an electron enters into the molecule. When the applied electric field strength to the molecule overcomes an energy increase in the final state, the transition probability increases abruptly. This causes the Coulomb staircase edges. The effective charge confined within a molecule is determined by the distance between a molecule and a substrate.

 

65.       S. Nishida and T. Sato

            "2 Kinds Of Motion Aftereffect Reveal Different Types Of Motion Processing"

            Invest. Ophthalmol. Vis. Sci. 34 (4), 1363-1363 (1993).

 

            ABSTRACT:

66.       O. Niwa, M. Morita, and H. Tabei

            "Highly Sensitive Small-Volume Voltammetry Of Reversible Redox Species With An Ida Electrochemical-Cell And Its Application To Selective Detection Of Catecholamine"

            Sens. Actuator B-Chem. 14 (1-3), 558-560 (1993).

 

            ABSTRACT:

67.       K. Nozawa and Y. Horikoshi

            "Misorientation In Gaas On Si Grown By Migration-Enhanced Epitaxy"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 32 (1B), 626-631 (1993).

 

            ABSTRACT: The misorientation of GaAs grown on Si(100) by migration-enhanced epitaxy is investigated using X-ray diffraction. In addition to the usual tilt misorientation of GaAs with respect to the Si substrate, almost all of the GaAs layers are found to exhibit a misorientation of rotation about the substrate surface normal. The misorientation depends systematically on the initial growth conditions such as the substrate off-orientation and the nucleation conditions of the first GaAs monolayer, which include growth initiations by Ga- or As-supply first and simultaneous supply of Ga and As4 with various V/III flux ratios. A model which describes the observed tilt is proposed, based on the relaxation of misfits perpendicular to the Si surface. Reducing unnecessary misorientation leads to better crystal quality even for thick (approximately 4 mum) samples including strained-layer superlattices, which can provide a very low dislocation density. The surface etch-pit densities are 6.2 X 10(4) cm-2 for the thick sample with a rotation angle beta = 2-degrees, and 3.1 x 10(5) cm-2 for beta = 12-degrees, even though they are grown under identical conditions except for the initial growth conditions.

 

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

            "Fermi-Edge Singularity In One-Dimensional Metals - Effects Of Hole Recoil And Electronic Correlation"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 32, 76-78 (1993).

 

            ABSTRACT: The Fermi-edge singularity in optical spectra is studied theoretically for one-dimensional (ID) metals. Using the intermediate-coupling method, the critical exponent is obtained analytically for an arbitrary mass of an optical hole. The electronic correlation is also taken exactly into account by the Tomonaga-Luttinger's bosonization technique. 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.

 

69.       T. Ogawa and A. Shimizu

            "Dimensional Crossover Of Excitons In One-Photon And 2-Photon Absorption Processes"

            Phys. Rev. B 48 (7), 4910-4913 (1993).

 

            ABSTRACT: We develop a theory of one- and two-photon absorptions (OPA and TPA) of Wannier excitons in the intermediate regime, where the dimensionality of the excitons is intermediate between one and two. We find that the TPA spectrum changes drastically with variations in the dimensionality, whereas the OPA spectrum keeps its qualitative nature. The theory explains the puzzling results of a recent experiment on the TPA spectrum of a quantum wire [R. Cingolani et al., Phys. Rev. Lett. 69, 1276 (1992)].

 

70.       K. Otsuka

            "Transverse Effects On Antiphase Laser Dynamics"

            Jpn. J. Appl. Phys. Part 2 - Lett. 32 (10A), L1414-L1417 (1993).

 

            ABSTRACT: Transverse effects on antiphase dynamics in a multi-longitudinal-mode solid-state laser are investigated experimentally We show a three-dimensional self-organization resulting from the cross saturation dynamics in the longitudinal and transverse directions, in which the intensity noise spectrum of partial output within the beam cross-section possesses the antiphase relaxation oscillation components inherent in multi-longitudinal-mode lasers and the noise spectrum changes along transverse direction, while these antiphase components vanish completely for the entire beam. Modulation dynamics in a multi-transverse-mode laser featuring transverse synchronization and clustering is also demonstrated.

 

71.       K. Otsuka, P. Mandel, M. Georgiou, and C. Etrich

            "Antiphase Dynamics In A Modulated Multimode Laser"

            Jpn. J. Appl. Phys. Part 2 - Lett. 32 (3A), L318-L321 (1993).

 

            ABSTRACT: Antiphase periodic oscillatlons and clustering in a modulated microchip multimode solid-state laser have been demonstrated experimentally. Chaotic relaxation oscillations featuring intermode statistical non-independence that result from cross-saturation dynamics among oscillating modes have been observed.

 

72.       K. Prabhakaran, Y. Kobayashi, and T. Ogino

            "Interference Of Agl Radiation In The Xps Of Si And Au Using An Al/Mg Twin Anode"

            J. Electron Spectrosc. Relat. Phenom. 63 (3), 283-288 (1993).

 

            ABSTRACT: We report the observation of ghost peaks in the X-ray photoelectron spectrum of Si and Au surfaces. In the XPS of Si excited by Mg Kalpha as well as Al Kalpha, a strong peak at 1144.6 eV kinetic energy was observed. Similarly, we observed ghost peaks in the spectrum of Au foil excited with Mg Kalpha and Al Kalpha at kinetic energies 945.6, 859.6, 778.6 and 693.6 eV. Detailed analysis of the anode employing XPS and electron probe micro analysis (EPMA) showed evidence for Ag contamination, which causes emission of Ag Lalpha and Lbeta radiations. All the ghost peaks have been explained as photoemission peaks originating from Ag Lalpha and Lbeta radiations. EPMA is seen to give more reliable information than XPS in characterising the contaminated anode.

 

73.       K. Prabhakaran, Y. Kobayashi, and T. Ogino

            "Chemically Prepared Oxides On Si(001) - An Xps Study"

            Surf. Sci. 290 (3), 239-244 (1993).

 

            ABSTRACT: Thin oxide. layers prepared on Si(001) by various chemical treatments have been investigated using X-ray photoelectron spectroscopy. The oxides are prepared by treatment with HCl, H2SO4 and HNO3. The O 1s spectra consists of two peaks at 532.6 eV (low binding energy component, LBC) and 533.6 eV (high binding energy component, HBC) in all the cases. The LBC is assigned to a monatomic bridging oxygen, Si-O-Si and HBC to a monatomic non-bridging oxygen, Si-O species. Conversion of Si-O to Si-O-Si takes place on annealing the sample. The concentration of Si-O species is low in the case of HCI oxide. In in situ prepared oxide, the O 1s is predominantly due to Si-O-Si.

 

74.       K. Prabhakaran, T. Nishioka, K. Sumitomo, Y. Kobayashi, and T. Ogino

            "Insitu Oxidation Of A Thin-Layer Of Ge On Si(001) - Observation Of Geo To Sio2 Transition"

            Appl. Phys. Lett. 62 (8), 864-866 (1993).

 

            ABSTRACT: A thin layer of Ge grown on Si(001) surface is oxidized in situ and investigated using XPS, AES, RHEED, and MEIS. The samples used are, Ge layer formed by deposition at room temperature and SiGe mixed layer formed by deposition at 550-degrees-C. Oxidation at 250-degrees-C of the RT grown layer leads to the formation of GeO and on heating the surface to 360-degrees-C, oxygen bonds with Si forming SiO2, thereby reducing GeO to elemental Ge. In the epitaxially grown layer (grown at 550-degrees-C), after oxidation, SiO2 and a small amount of GeO are formed. Similar reaction takes place on this surface also, forming SiO2 as the final product on the surface. In the RT grown layer, after oxidation, MEIS shows evidence for the diffusion of Si through the Ge layer towards the surface.

 

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

            "Migration-Enhanced Epitaxial-Growth Of Gaas On Si Using (Gaas)1-X(Si2)X/Gaas Strained-Layer Superlattice Buffer Layers"

            J. Vac. Sci. Technol. B 11 (3), 820-822 (1993).

 

            ABSTRACT: (GaAs)1-x(Si2)x/GaAs strained-layer superlattices (SLS) have been used as buffer layers to reduce the dislocation density in GaAs grown on Si by migration-enhanced epitaxy. The cross-sectional transmission electron microscopy (TEM) investigations revealed extensive threading dislocation bending at each interface of (GaAs)1-x(Si2)x and GaAs, making the SLS highly efficient. The observed highly effective dislocation bending, it is believed that due to a combined effect of built-in strain in the SLS and the relatively high elastic stiffness constant of (GaAs)1-x(Si2)x alloys. Plan-view TEM studies indicated dislocation densities < 10(6) cm-2 at a distance of 0.2 mum from the surface of GaAs on Si.

 

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

            "Migration Enhanced Epitaxy Growth Of Gaas On Si With (Gaas)1-X(Si2)X/Gaas Strained Layer Superlattice Buffer Layers"

            Appl. Phys. Lett. 62 (2), 154-156 (1993).

 

            ABSTRACT: (GaAs)1-x(Si2)x/GaAs strained-layer superlattices (SLS) have been used as buffer layers to reduce the dislocation density in GaAs grown on Si by migration enhanced epitaxy (MEE). Double-crystal x-ray diffractograms of GaAs on Si grown using MEE with 3 packets of 5 period (GaAs)1-x(Si2)x/GaAs SLS buffer layers, exhibited a GaAs (004) peak full width at half maximum value of 150 arcsecs. The cross-sectional transmission electron microscopy investigations revealed extensive threading dislocation bending at each interface of (GaAs)1-x(Si2)x and GaAs, making the SLS highly efficient. The observed highly effective dislocation bending, we believe is due to a combined effect of built-in strain in the SLS and the relatively high elastic stiffness constant of (GaAs)1-x(S2)x alloys. Plan-view transmission electron microscopy studies indicated dislocation densities < 5 X 10(5) cm-2 at a distance of 0.2 mum from the surface of GaAs on Si.

 

77.       H. P. C. Robinson, M. Kawahara, Y. Jimbo, K. Torimitsu, Y. Kuroda, and A. Kawana

            "Periodic Synchronized Bursting And Intracellular Calcium Transients Elicited By Low Magnesium In Cultured Cortical-Neurons"

            J. Neurophysiol. 70 (4), 1606-1616 (1993).

 

            ABSTRACT: 1. In Mg2+-free external solution, rat cortical neurons in cultured networks entered a stable firing mode, consisting of regular bursts of action potentials superimposed on long-lasting depolarizations. The average separation between bursts varied from culture to culture, but was usually between 5 and 20 s. The distribution of burst intervals followed a Gaussian or normal distribution, with a standard deviation of typically 10% of the average burst period. 2. A gradually depolarizing pacemaker potential was never observed between bursts, but the threshold for action potentials during the quiescent phase was greater-than-or-equal-to 10 mV above the resting potential. No progressive change in conductance or excitability was observed during the quiescent period. Intracellular stimulation of action potentials did not reproduce the long-lasting depolarization. 3. Switching from current clamp to voltage clamp at the resting potential revealed large postsynaptic currents, mainly excitatory but with a small inhibitory component, at the same phase and frequency as the spike bursts, showing that periodic synaptic input is responsible for the burst-depolarizations. The current could be eliminated by local application of 2-amino-5-phosphonovaleric acid (APV) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) to the postsynaptic cell. In the presence of tetrodotoxin, irregular miniature excitatory postsynaptic currents were observed. 4. A fluorescent calcium indicator (fluo-3, 100 muM) was included in the whole-cell pipette solution, to allow simultaneous electrical and calcium measurements in the same cell. In current clamp, transient intracellular calcium increases were found, which were synchronized to the spike bursts. The Ca2+ rise lasted as long as the action potential burst, and was followed by an exponential decay considerably slower than that of the membrane potential. Calcium transients disappeared during voltage clamp at the resting potential, suggesting that calcium influx through voltage-dependent calcium channels greatly exceeds that through synaptic channels. 5. Multisite Ca2+ recording, after loading with fluo-3 acetoxymethyl (AM) ester, revealed that the onsets of burst-related calcium transients were synchronized in all active cells of each view-field, to within approximately 20 ms. Occasionally, secondary rhythms were observed in which only a subset of cells participated. The times to peak and the decay times of calcium transients varied among synchronized cells. 6. The pharmacology of the burst-related calcium transients was investigated by bath application of a variety of compounds. Tetrodotoxin (1 muM) produced reversible inhibition of transients, as did APV (100 muM) and Mg2+ (1 mM), implying that voltage-dependent sodium channels and N-methyl-D-aspartate (NMDA) receptor-mediated channels are essential. Bicuculline (20 muM) and strychnine (20 muM) both produced a reversible increase in the burst period, sometimes with a slight increase in the amplitude of transients, whereas muscimol (10 muM) reversibly arrested the transients. 7. To investigate the timing of action potential firing at many sites, we cultured cells on substrates with embedded arrays of transparent electrodes. Simultaneous recordings at up to eight sites showed extracellular action potential bursts coincident with intracellular action potentials. Differences in burst initiation times of approximately 20 ms were observed at physical separations of approximately 1 mm. The order of burst initiation at different channels and the detailed firing pattern changed from burst to burst, implying that the wave of excitation was initiated randomly. 8. The phase of periodic bursting could be locked to stimulating current pulses passed through individual sites in the electrode array, and periodic bursting could be initiated in silent cultures. 9. These results indicate that the periodic spike bursts and intracellular calcium transients are generated by periodic excitatory synaptic conductance transients, with a slow NMDA receptor-mediated component. The depolarization opens voltage-dependent calcium channels and the resulting calcium elevation persists during the interburst quiescent period. The random direction and timing of excitation and the lack of any observed pacemaker potential in cells could be explained if the prevalent spontaneous miniature excitatory synaptic events and tonically active NMDA channels act as random sources of excitation.

 

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

            "Periodic Bursting Of Cultured Cortical-Neurons In Low Magnesium - Cellular And Network Mechanisms"

            Jpn. J. Physiol. 43, S125-S130 (1993).

 

            ABSTRACT: The origin of the 0.1 Hz bursting of cultured rat cortical neurons in zero Mg2+ was studied by whole-cell recording, fluo-3 Ca2+ imaging, and multi-unit electrode array recording. A model is proposed in which spontaneous synaptic currents act as a random pacemaker.

 

79.       H. Saito, K. Uwai, and N. Kobayashi

            "Gaas Quantum-Wire Laser Using Fractional Layer Superlattice"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 32 (10), 4440-4445 (1993).

 

            ABSTRACT: In (AlAs)k/n(GaAs)l/n (k+l=n) fractional layer superlattice (FLS) growth on the (001) GaAs vicinal surface 2-degrees off toward [110BAR] by metal-organic chemical vapor deposition, using a (AlAs)m(GaAs)n(m, n<3) short period superlattice as the buffer layer very much improve the uniformity of lateral periodicity in the FLS near the FLS/buffer interface compared with using binary (GaAs and AlAs) and ternary AlGaAs as the buffer layers. This is due to the improvement in the uniformity of the terrace width on the surface of a short period superlattice by step-ordering. As a result, a large polarization anisotropy of about 50% is observed in the photoluminescence spectrum for the quantum-wire array structure oriented toward [110] in which a 4-nm-thick (AlAs)1/4(GaAS)3/4 FLS layer is sandwiched by (AlAs)3(GaAs)3 short period superlattice layers. Separated confinement heterostructures consisting of a 12-nm-thick undoped (AlAs)1/4(GaAs)3/4 FLS quantum-wire active layer, doped (AlAs)1(GaAS)2 carrier confinement layers, and doped Al0.6Ga0.4As optical confinement layers are grown. To prevent the disordering of the FLS layer induced by the diffusion of intentionally doped impurity atoms during the growth and the processing, low-diffusive Si and C atoms are used for n- and p-type doping into carrier and optical confinement layers. Lasing operation is obtained by current injection below 195 K for the electrode with simple stripe geometry. The lasing wavelength depends on the orientation of the stripe electrode. The electrode with [110] orientation which is parallel to the quantum wire array has a lasing wavelength of 662 nm, and the [110BAR] orientation which is perpendicular to the array has a lasing wavelength of 667 nm at 10 K.

 

80.       H. Saito, K. Uwai, Y. Tokura, and T. Fukui

            "Step Ordering During Fractional-Layer Superlattice Growth On Gaas(001) Vicinal Surfaces By Metalorganic Chemical-Vapor-Deposition"

            Appl. Phys. Lett. 63 (1), 72-74 (1993).

 

            ABSTRACT: Step ordering during fractional-layer superlattice (FLS) growth is observed by transmission electron microscopy. A cross-sectional transmission electron micrograph of an (AlAs)1/2(GaAs)1/2FLS shows that the steps of unequal spacings observed on a GaAs surface develop a sequence of uniformly spaced steps of single monolayer height during the growth. Comparison of the observed FLS structure with a numerical simulation based on the assumption of unequal incorporation probabilities of adatoms into up steps and down steps shows that a net flux into the up steps 2%-4% larger than that into the down steps is enough to reproduce the FLS growth. It is demonstrated that the FLS growth provides a unique opportunity to observe the step ordering process directly and determine the anisotropy of diffusion quantitatively.

 

81.       E. T. Sano and Y. Horikoshi

            "Se Adsorption On (001) Gaas Under Various As4-Pressures"

            Jpn. J. Appl. Phys. Part 2 - Lett. 32 (5A), L641-L644 (1993).

 

            ABSTRACT: We used reflection high-energy electron diffraction (RHEED) to investigate the adsorption of Se on (001) GaAs surfaces under different residual As4 pressures at a substrate temperature of 510-degrees-C. Under a fixed Se pressure of 5 x 10(-9) Torr, the diffraction pattern showed a (2 x 4) reconstruction when the AS4 pressure was 5 x 10(-8) Torr. When the AS4 pressure was reduced to the level of Se pressure, the surface showed (4 x 3) reconstruction. When the AS4 pressure was further reduced to 5 x 10(-10) Torr, the diffraction spots in the RHEED pattern disappeared, and a halo pattern became dominant. These results show that even at a fixed substrate temperature, the surface structure of Se-adsorbed (001) GaAs can be sensitively changed by varying the AS4 pressure.

 

82.       T. Sato and S. Nishida

            "2nd-Order Depth-Perception With Texture-Defined Random-Check Stereograms"

            Invest. Ophthalmol. Vis. Sci. 34 (4), 1438-1438 (1993).

 

            ABSTRACT:

83.       H. Shaked, J. D. Jorgensen, B. A. Hunter, R. L. Hitterman, K. Kinoshita, F. Izumi, and T. Kamiyama

            "Defect Structure And Superconducting Properties Of La1.8srxca1.2-Xcu2o6-Delta"

            Phys. Rev. B 48 (17), 12941-12950 (1993).

 

            ABSTRACT: We have studied the relationship between structural defects and superconductivity in La1.8SrxCa1.2-xCu2O6-delta (0 less-than-or-equal-to x less-than-or-equal-to 0.8). The samples were prepared by synthesis under different oxygen Pressures, P(O2) = 50, 250, and 400 atm. Six of the seven samples were found to be superconducting with 22 less-than-or-equal-to T(c) less-than-or-equal-to 58 K. The structural properties were determined by neutron powder diffraction. The inter-CuO2-plane spacing, d(Cu-Cu), increases as Ca on the M(1) site between these planes is replaced by the larger Sr and La ions. The metal-site ordering is influenced by the oxygen pressure during synthesis. We have used the inter-CuO2-plane spacing, neutron-diffraction measurements of the scattering from the metal sites, and chemical constraints to determine the occupancies of La, Sr, and Ca at the M(1) site. For the same overall composition, higher oxygen pressure leads to a larger fraction of La on the M(1) site. Oxygen occupancy of the vacant O(3) site in the M(1) plane increases sharply when d(Cu-Cu) exceeds 3.5 angstrom. The superconducting transition temperature T(c) decreases systematically as the occupancy of O(3) increases for samples that would otherwise be expected to be superconducting.

 

84.       H. Shibata, T. Watanabe, K. Kinoshita, A. Matsuda, and T. Yamada

            "Infrared Reflectivity Of La1.89ca1.11cu2o6-Plus-Or-Minus-Delta Single-Crystals At Various O2 Annealing Pressures"

            Phys. Rev. B 48 (18), 14027-14030 (1993).

 

            ABSTRACT: The ab-plane reflectivity of La1.89Ca1.11Cu2O6+/-delta single crystals, whose properties change from semiconductor to superconductor under high-oxygen-pressure annealing, is measured between 250 and 20000 cm-1 at room temperature. Although the annealing increases the oxygen content very slightly, the spectra change in the same way as seen in other cuprates with carrier doping: a charge-transfer peak disappears and low-energy excitation increases. We suggest the possibility that holes in the apex oxygen redistribute to the CuO2 planes. Mid-infrared absorption is observed in all samples. Relation between the mid-infrared absorption and the influence of La and Ca disorder on the CuO2 planes is also discussed.

 

85.       T. Sogawa, S. Ando, and H. Kanbe

            "Gaas/Alas Trench-Buried Quantum Wires (Less-Than-20nmx20nm) Fabricated By Metalorganic Chemical-Vapor-Deposition On Nonplanar Substrates"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 32 (12B), 6224-6227 (1993).

 

            ABSTRACT: We report the fabrication of quantum wires buried in U-grooved trenches grown by metalorganic chemical vapor deposition on V-grooved (001) substrates. These trench structures with vertical (110) sidewalls were formed as a result of the faceting of (110) planes, and lateral growth of these planes reduced the trench width to less than 20 nm. A cross-sectional scanning electron micrograph shows that these trench-buried structures have GaAs wires of about 20 nm lateral width. Photoluminescence (PL) blue shifts and strong PL anisotropy confirm two-dimensional quantum confinement.

 

86.       A. Sugimura

            "Effect Of Reservoir-Electron Motion On The Frequency-Response Of Double-Barrier Resonant-Tunneling"

            Phys. Rev. B 47 (15), 9676-9683 (1993).

 

            ABSTRACT: The frequency response of the double-barrier resonant-tunneling current to the bias-voltage modulation is studied theoretically taking into account the effect of the dynamic motion of reservoir electrons in the contacts. A density-matrix approach with a transfer Hamiltonian is used and the incoherent scatterings in the contacts are modeled with damping constants. It is shown that the bandwidth of the device is determined not only by the electron-transfer rates through the barriers but also by the phase-smearing rates for the tunneling electrons. It is also shown that the frequency response of the tunneling current exhibits resonance enhancements in the high-frequency region. The enhancements are attributed to the quantum oscillations of the electrons between the quantum well and contact regions.

 

87.       M. Suzuki, H. Hibino, Y. Homma, T. Fukuda, T. Sato, M. Iwatsuki, K. Miki, and H. Tokumoto

            "Real-Time Observation Of (1x1)-(7x7) Phase-Transition On Vicinal Si(111) Surfaces By Scanning-Tunneling-Microscopy"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 32 (7), 3247-3251 (1993).

 

            ABSTRACT: Scanning tunneling microscopy of a Si(111) surface with a misorientation of 10-degrees reveals that the (7 x 7) domains form stripes whose widths are quantized in units of a (7 x 7) unit cell. The (7 x 7)-to-(1 x 1) phase transition on this surface occurs at about 1030 K when the temperature is increased, which is about 80 K lower than that for a nominally flat Si(111) surface, and the (1 x 1)-to-(7 x 7) phase transition occurs at 1003 K when the temperature is reduced. Nucleation and growth of (7 x 7) domains are explained in terms of the domains' energy gain and the energy loss of the domain edges and slant surfaces.

 

88.       M. Suzuki, Y. Homma, H. Hibino, T. Fukuda, T. Sato, M. Iwatsuki, K. Miki, and H. Tokumoto

            "Real-Time Scanning-Tunneling-Microscopy Of Phase-Transition And Faceting On A Vicinal Si(111) Surface"

            J. Vac. Sci. Technol. A-Vac. Surf. Films 11 (4), 1640-1643 (1993).

 

            ABSTRACT: We have used scanning tunneling microscopy for real-time observation of the (7 X 7) reconstruction on a Si(111) vicinal surface misoriented by 10-degrees toward [112BAR]. The (1 X 1)-(7 X 7) reconstruction corresponds to the formation of the (7 X 7) stripes perpendicular to the misorientation direction, and the width of the stripe is quantized in half units of (7 X 7) mesh. Moreover the (1 X 1)-(7 X 7) transition on the vicinal surface takes place at a temperature about 80-degrees lower than that for the flat surface. As the temperature is decreased, further phase separation takes place, changing the vicinal surface into a (111) facet and a slanting surface. On the (111) facet the (7 x 7) or (5 X 5) structure is formed, while the slanting surface becomes a (331) facet that shows (12 X 1) periodic structure.

 

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

            "Microdisk Array Electrode Based On Carbonized Poly (P-Phenylene Vinylene) Film"

            Denki Kagaku 61 (7), 820-822 (1993).

 

            ABSTRACT:

90.       A. Taguchi, M. Kawashima, K. Takahei, and Y. Horikoshi

            "Er Luminescence-Centers In Gaas Grown By Migration-Enhanced Epitaxy"

            Appl. Phys. Lett. 63 (8), 1074-1076 (1993).

 

            ABSTRACT: Er-doped GaAs has been grown by migration-enhanced epitaxy. The samples were grown at 300, 400, and 500-degrees-C. Secondary ion mass spectroscopy measurements showed that the Er concentration in the grown epitaxial layer does not depend on the growth temperature between 300 and 500-degrees-C. All samples showed luminescence due to the Er intra-4f-shell transition from the I-4(13/2) excited state to the I-4(15/2) ground state, but the spectra change drastically when the growth temperature is increased from 300-degrees-C to 400 or 500-degrees-C. The photoluminescence spectra of the samples grown above 400-degrees-C are simpler than that of the sample grown at 300-degrees-C. The spectrum of the sample grown at 300-degrees-C became broad after annealing, whereas the spectra of the samples grown at 400-degrees-C and above showed only changes in the relative intensity of the main luminescence lines. Some thermally stable Er luminescence centers seem to be preferentially formed at 400 and 500-degrees-C.

 

91.       T. Takagahara

            "Electron-Phonon Interactions And Excitonic Dephasing In Semiconductor Nanocrystals"

            Phys. Rev. Lett. 71 (21), 3577-3580 (1993).

 

            ABSTRACT: The size dependence of the contribution to the excitonic dephasing rate in semiconductor nanocrystals is clarified for various electron-phonon coupling mechanisms. On the basis of these dependencies, the commonly observed linearly temperature-dependent term of the excitonic dephasing rate and the proportionality of its magnitude to the inverse square of the nanocrystal size are attributed to pure dephasing due to deformation-potential coupling. The calculated coefficients of the linearly temperature-dependent term are quantitatively in good agreement with the experimental results on CdSe and CuCl nanocrystals.

 

92.       T. Takagahara

            "Nonlocal Theory Of The Size And Temperature-Dependence Of The Radiative Decay-Rate Of Excitons In Semiconductor Quantum Dots"

            Phys. Rev. B 47 (24), 16639-16642 (1993).

 

            ABSTRACT: A nonlocal theory of the radiative decay rate of excitons in semiconductor quantum dots is developed and the observed size and temperature dependence for CuCl microcrystallites is explained successfully. The retardation effect due to the finite ratio of the quantum dot radius to the wavelength of light is found to be irrelevant for explaining the experiments. Instead, the homogeneous broadening effect is shown to be essential in saturating the mesoscopic enhancement of the excitonic radiative decay rate or, in other words, in determining the effective exciton coherence length.

 

93.       T. Takagahara

            "Effects Of Dielectric Confinement And Electron-Hole Exchange Interaction On Excitonic States In Semiconductor Quantum Dots"

            Phys. Rev. B 47 (8), 4569-4585 (1993).

 

            ABSTRACT: A general scheme is established within the effective-mass approximation to calculate systematically the excitonic energy spectra in a semiconductor quantum dot including the dielectric confinement effect. This effect is found to appear most pronounced in the quantum-dot structure in comparison with the quantum-well and quantum-wire structures. A formula of the lowest exciton energy in the strong confinement regime is derived and the significance of the dielectric confinement effect is clarified. We investigate the dependence of the binding energy and the oscillator strength of the lowest-energy excitonic state on the quantum-dot radius, the electron-to-hole mass ratio, and the dielectric-constant ratio between the quantum dot and the surrounding medium. The subband mixing effect due to the electron-hole Coulomb interaction gives a finite oscillator strength to excitonic transitions which are forbidden in the absence of the Coulomb interaction. This effect is shown unambiguously in the calculated excitonic energy spectra. Furthermore, the electron-hole exchange interaction in a quantum dot is discussed. The short-range part of the exchange energy is shown to increase in proportion to the inverse of the volume of the quantum dot as the quantum-dot size is reduced. On the other hand, the long-range part of the exchange energy is found to be sensitively dependent on the shape of the quantum dot. In particular, it vanishes for the optically allowed excitonic states in a spherical quantum dot.

 

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

            "Direct Sequencing Of Pcr Products Using Unlabeled Primers"

            Biotechniques 14 (2), 218-221 (1993).

 

            ABSTRACT: An improved protocol is described for using lambda exonuclease to directly sequence PCR products. It is important not to execute PCR cycles beyond the plateau of amplification. The asymmetric PCR and double-stranded DNA sequencing by a snaP-cooling Procedure were also performed using the same DNA samples and primers. The improved method was the most reliable and produced the best results.

 

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

            "Highly Sensitive Detection Of Catecholamine With Interdigitated Array Microelectrodes In Hplc"

            Sens. Actuator B-Chem. 13 (1-3), 336-339 (1993).

 

            ABSTRACT: The highly sensitive detection of catecholamine has been achieved by using an interdigitated array (IDA) microelectrode as an electrochemical detector in a microbore high-performance liquid chromatography (HPLC) system. The current responses for catecholamine are measured for IDA electrodes with different gaps between their adjacent band electrodes. An IDA electrode with a narrow pp produces a high current density and reduces the influence of the auxiliary electrode position on the current response. The current response measured for an IDA electrode incorporated in the microbore HPLC system is about four times greater than that measured for a combination of the same IDA electrode and an ordinary sized column due to current enhancement by redox cycling in the slower stream.

 

96.       K. Takahei and A. Taguchi

            "Selective Formation Of An Efficient Er-O Luminescence Center In Gaas By Metalorganic Chemical-Vapor-Deposition Under An Atmosphere Containing Oxygen"

            J. Appl. Phys. 74 (3), 1979-1982 (1993).

 

            ABSTRACT: To investigate the effects of oxygen codoping on Er luminescence centers in GaAs, we grew Er-doped GaAs by low-pressure metalorganic chemical vapor deposition (MOCVD) and measured the photoluminescence spectrum due to the intra-4f-shell transition of Er. The spectrum of a sample grown in a pure hydrogen atmosphere was complicated, showing many lines and bands. The spectrum of a sample grown in a hydrogen atmosphere containing 0.2 ppm oxygen, on the other hand, was simple and had few lines. The spectrum of the oxygen-codoped sample showed higher peak intensities as well as higher integrated luminescence intensity in the 1.5-1.6 mum region. Secondary-ion mass spectroscopy revealed that the oxygen-codoped sample had a higher concentration of oxygen, indicating the formation of an Er-O complex center. One kind of optically active efficient Er-O complex luminescence center can, therefore, be selectively formed under suitable MOCVD growth conditions.

 

97.       H. Takayanagi, T. Akazaki, and J. Nitta

            "Superconducting Structures On Narrow-Gap Semiconductors"

            Semicond. Sci. Technol. 8 (1), S431-S434 (1993).

 

            ABSTRACT: Nb/n-type InAs/Nb superconducting devices with oxide-free interfaces are fabricated to study the interface effect on the superconducting characteristics of the device. The maximum supercurrent as well as the maximum supercurrent-normal resistance product is enhanced by RF sputter cleaning of the InAs surface. Using a device where Nb is deposited on InAs without breaking the vacuum, the carrier concentration dependence of the proximity-effect-induced pair potential is obtained. This dependence is consistent with the theory if some assumptions are made.

 

98.       K. Takeda and K. Shiraishi

            "Electronic-Structure Of Silicon-Oxygen High Polymers"

            Solid State Commun. 85 (4), 301-305 (1993).

 

            ABSTRACT: The electronic structure of silicon-oxygen high polymers (siloxane and siloxene) have been calculated by the first-principle local-density-functional method. Oxygen's lone-pair (OLP) states play an important role in the electronic structure of these polymers, in accordance with oxygen's spatial position. In siloxane, where oxygen atoms position in the Si skeleton backbone, non-bonding (n) electrons in the OLP states cut Si's sigma-electron delocalization, and widen the band gap. On the contrary, when oxygen atoms are located outside of the Si skeleton (siloxene), the characteristic sigma-n mixing occurring at the band-edge states has a potential to reduce the band gap.

 

99.       K. Takei, J. Suzuki, Y. Maeda, and S. Funahashi

            "Microstructural Analysis Of Cocr Thin-Films By Small-Angle Neutron-Scattering"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 32 (6A), 2665-2666 (1993).

 

            ABSTRACT: Small-angle neutron scattering is applied to the analysis of latent microstructures in compositionally separated CoCr thin films. A fine in-grain structure less than 10 nm in size is observed in a film deposited at 200-degrees-C using small-angle scattering. This structure coincides with that observed by means of transmission electron microscopy (TEM) in chemically etched thin films. The fine in-grain structure disappears when the deposition temperature is increased to 400-degrees-C. This experiment confirms the existence of latent microstructures in CoCr films and reveals that further analysis of magnetic microstructures is possible using neutron scattering.

 

100.    Y. Tanaka, A. Hasegawa, and H. Takayanagi

            "Energy-Spectrum Of The Quasi-Particle In A Quantum Dot Formed By A Superconducting Pair Potential Under A Magnetic-Field"

            Solid State Commun. 85 (4), 321-326 (1993).

 

            ABSTRACT: Basic properties of the quantum dot structure, which represents a normal region created inside the superconducting matter on a subnanometer scale, are predicted. The bound-states of the quasiparticle formed by the superconducting pair potential is calculated under a magnetic field. The spatial dependence of the pair potential and the current density are determined selfconsistently. The bound-state is found to be change dramatically as the number of the magnetic flux quanta changes one by one.

 

101.    M. Taniguchi and K. Takahei

            "Optical-Properties Of The Dominant Nd Center In Gap"

            J. Appl. Phys. 73 (2), 943-947 (1993).

 

            ABSTRACT: The optical properties of the Nd centers in Nd-doped GaP samples grown by metalorganic chemical vapor deposition have been studied. By using resonant photons to excite the Nd ions directly, we found that the energy separations between the spin-orbit-splitting levels are smaller for Nd in GaP when compared with the corresponding energy separations of Nd in ionic crystals. The crystal field-induced splittings of the dominant Nd center are also found to be smaller compared with the splittings of the other Nd centers in the GaP host. The luminescence lifetime value as a function of sample temperature was also studied. It was found that the luminescence lifetime value of the dominant Nd center remains at a constant 25 mus up to 150 K and becomes smaller as the sample temperature is further increased.

 

102.    S. Tarucha, T. Saku, Y. Tokura, and Y. Hirayama

            "Sharvin Resistance And Its Breakdown Observed In Long Ballistic Channels"

            Phys. Rev. B 47 (7), 4064-4067 (1993).

 

            ABSTRACT: Ballistic transport is studied for relatively narrow channels formed in a high-mobility modulation-doped heterostructure. Sharvin resistance is observed in the constricted channel, whose length is extended to 20 mum as the effective width is decreased to 1.5 mum. This is related to the effect of lateral restriction imposed on the high-mobility structure. We also find a strong reduction of the differential channel resistance at a small applied voltage.

 

103.    Y. Tomioka, M. Naito, and K. Kitazawa

            "The Meissner And Shielding Effects In Niobium In Relation To Oxide Superconductors"

            Physica C 215 (3-4), 297-304 (1993).

 

            ABSTRACT: To examine the dependence of the Meissner and shielding effects on vortex pinning, ZFC and FC curves were measured on polycrystalline niobium samples with different pinning strengths. The Meissner fraction was almost unity for the annealed sample from which pinning centers were removed whereas it was much smaller for the unannealed one. The ZFC and FC curves of the unannealed one were discussed in terms of pinning. From the field dependent Meissner fraction of the unannealed samples the T dependence of critical current density was estimated and compared with that of high-T(c) superconductors.

 

104.    M. Ueda and A. Shimizu

            "Nonequilibrium Current Noise Spectrum In A Dissipative Conductor"

            J. Phys. Soc. Jpn. 62 (9), 2994-2998 (1993).

 

            ABSTRACT: We study the noise spectrum of electrical current in a voltage-biased conductor. At low frequencies, the noise power in a nondissipative conductor is below the standard quantum limit which typically appears in tunnel junctions. Energy dissipation in the conductor further reduces the low-frequency noise power, nearly to zero when the dissipation is strong enough. At high frequencies, however, the noise is no longer suppressed, and the noise power approaches the standard quantum limit irrespective of the strength of energy dissipation.

 

105.    K. Uwai, H. Saito, Y. Yamauchi, and N. Kobayashi

            "Arsenic Coverages And Surface-Structures Of As-Stabilized Gaas (001) Surfaces During Metalorganic Chemical-Vapor-Deposition Observed By Reflectance Difference"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 32 (12A), 5479-5486 (1993).

 

            ABSTRACT: We study temporal evolutions of surface anisotropy change detected optically at wavelengths of 633 nm and 488 nm during the formation of Ga-stabilized surfaces to characterize As-stabilized (001) GaAs surfaces grown by metalorganic chemical vapor deposition (MOCVD). Using the evolution of Ga dimer concentration, we find that effective As coverages, which are defined as the amount of As on the surface that can be incorporated into the crystal, are close to 1 for the c(4 x 4) surface and As-richer surfaces, although these surfaces have actual As coverages of more than 1. We also find that three kinds of well-defined As-stabilized surfaces with different As coverages, c(4 x 4)+alpha, c(4 x 4), and (2 x 4), can exist in MOCVD environments depending on the AsH3 partial pressures, with c(4 x 4)+alpha being a c(4 x 4)-like surface with additional As. A fast As desorption with a time constant of <0.5 s at 600-degrees-C and at 570-degrees-C accompanies the conversion from c(4 x 4)+alpha to c(4 x 4). Another As desorption with a time constant of 2 s at 600-degrees-C and 4 s at 570-degrees-C accompanies the conversion from c(4 x 4) to the least-As-rich (2 x 4) surface with theta(As)=0.6-0.7.

 

106.    N. Vanderpost, J. Nitta, and H. Takayanagi

            "Elastic-Scattering And The Current-Voltage Characteristics Of Superconducting Nb-Inas-Nb Junctions"

            Appl. Phys. Lett. 63 (18), 2555-2557 (1993).

 

            ABSTRACT: Superconducting niobium contacts are attached to a 0.8-mum-long epitaxially grown InAs channel sandwiched between insulating InGaAs layers. The current-voltage characteristics show nonlinearities at submultiples of the superconducting energy gap indicative of multiple-Andreev reflections. We demonstrate that an increase in the elastic scattering rate in the InAs channel, caused by Ar-ion etching, diminishes the order of Andreev reflections and explains the overall shape of the current-voltage characteristics.

 

107.    K. Watanabe, H. Iwamura, and Y. Yamamoto

            "Effect Of Additive-Pulse Mode-Locking On An External-Cavity Surface-Emitting Ingaas Semiconductor-Laser"

            Opt. Lett. 18 (19), 1642-1644 (1993).

 

            ABSTRACT: The effect of additive-pulse mode locking on a semiconductor laser is studied experimentally. We reduced the pulse duration from 19 to 6 ps with an external auxiliary cavity containing a 1.3-m fiber in a synchronously pumped external-cavity surface-emitting In0.53Ga0.47As laser. The relatively weak effect of additive-pulse mode locking on pulse shortening is primarily due to the large gain cross section of the semiconductor active medium in this system.

 

108.    T. Watanabe, K. Kinoshita, and A. Matsuda

            "Effects Of High-Oxygen-Pressure Annealing On Transport-Properties For La1.89ca1.11cu2o6+/-Delta Single-Crystals"

            Phys. Rev. B 47 (17), 11544-11547 (1993).

 

            ABSTRACT: We have measured in-plane resistivities rho(ab)(T), out-of-plane resistivities rho(c)(T), and Hall coefficients R(H)(T) of La1.89Ca1.11Cu2O6+/-delta single crystals as a function of temperature for various O2 annealing pressures. As-grown La1.89Ca1.11Cu2O6+/-delta single crystals which are semiconducting become superconducting if they are annealed under high oxygen pressures of more than 100 atm. In each metallic sample, the Hall angles reasonably fit Anderson's formula Cottheta(H) = alphaT2+C (alpha and C are constants and T is temperature). The phenomenological analysis using this relationship showed that the increase in T(c) produced by the annealing mainly results from a reduction in the impurity scattering, while the metallic conduction itself is achieved by an increase in the carrier concentration.

 

109.    M. Weyers and M. Sato

            "Growth Of Gaasn Alloys By Low-Pressure Metalorganic Chemical Vapor-Deposition Using Plasma-Cracked Nh3"

            Appl. Phys. Lett. 62 (12), 1396-1398 (1993).

 

            ABSTRACT: We present a letter on the growth of GaAs1-xNx alloys (0 < x < 0.016). The layers have been grown by metalorganic chemical vapor deposition at very low pressure (25 Pa). The nitrogen source NH3 has been decomposed in a remote microwave plasma, and uncracked triethylgallium and AsH3 were used. The N uptake into the layers shows a strong dependence on the growth temperature. The competition for the group V lattice sites leads to a reduction of the N content at higher AsH3 fluxes. The GaAsN layers show a strong red shift of the photoluminescence with increasing N content.

 

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

            "Boundary-Controlled Quantum Transport In Narrow Wires"

            Solid State Commun. 85 (7), 573-577 (1993).

 

            ABSTRACT: Transport properties of a quasi-ballistic wire with a point-contact (PC) in one-side boundary were studied. In the two-terminal resistance of the wire, when the width were sufficiently narrow, we have observed two competing sets of plateaus. They were able to be distinguished with each other by their different behaviours against variations of a sample size as well as a boundary condition. One of the plateau sets among them was found to originate from the PC itself in the wire boundary. This result indicates a possibility of a new class of narrow wires having a specific transport property due to the tailored quantum boundaries connecting with reservoirs or another wires.

 

111.    H. Yamaguchi and Y. Horikoshi

            "Step Motion And As Desorption On Inas(001) Surfaces Observed By Scanning-Tunneling-Microscopy"

            Phys. Rev. B 48 (4), 2807-2810 (1993).

 

            ABSTRACT: Step motion and As desorption on InAs(001) surfaces are directly observed by scanning tunneling microscopy at high temperatures. Stable (2x4) structures are observed even at temperatures high enough to cause the motion of monomolecular steps and kinks. At higher temperatures, domains with dark contrast (As-desorbed regions) are clearly observed. These results differ from those for GaAs surfaces and indicate strong lateral interaction in (2x4) structures on InAs.

 

112.    H. Yamaguchi and Y. Horikoshi

            "Phase-Transition On Iii-V Compound Semiconductor Surfaces Observed By An Improved Rheed Technique"

            J. Cryst. Growth 127 (1-4), 976-980 (1993).

 

            ABSTRACT: This paper determines quantitatively the electron-beam specular reflectivity of GaAs and InAs (001) surfaces at several temperatures by measuring the current through an electrode in front of a fluorescence screen. At the reconstruction transition, the reflectivity as a function of substrate temperature changes discontinuously with a hysteresis loop for InAs, but changes continuously without hysteresis for GaAs. This difference indicates that the order of surface structure transition differs between these two surfaces. The hysteresis width for InAs is smaller with misoriented surface than with an exactly oriented one. Monte Carlo simulation indicates that this phenomenon can be explained by assuming different As-As interactions along the surface.

 

113.    H. Yamaguchi and Y. Horikoshi

            "Influence Of Monomolecular Steps On The 1st-Order Structure Transition Of An Inas(001) Surface"

            Phys. Rev. Lett. 70 (9), 1299-1302 (1993).

 

            ABSTRACT: The surface stoichiometry transition from As-covered 2x4 to In-covered 4x2 on InAs(001) misoriented surface is studied by reflection high-energy electron diffraction. The width of the hysteresis due to the first-order phase transition between these two structures is smaller with a surface misoriented toward the [110BAR] direction than that with an exactly oriented surface. The results from Monte Carlo simulation indicate that this phenomenon can be explained by the finite size effect on the first-order surface stoichiometry transition caused by the existence of monomolecular steps.

 

114.    H. Yamaguchi, M. Kasu, T. Sueyoshi, T. Sato, and M. Iwatsuki

            "Observation Of Gaas (001) Surfaces At High-Temperatures By Scanning-Tunneling-Microscopy"

            J. Cryst. Growth 127 (1-4), 1064-1067 (1993).

 

            ABSTRACT: The structure of a GaAs (001) surface is studied by scanning tunneling microscopy at high sample temperatures up to 500-degrees-C. Below 460-degrees-C, a stable missing dimer row structure is clearly observed. At 480-degrees-C, however, the observed structures become disordered and change shape from image to image. This indicates that the thermal motion causes the migration of surface atoms as well as the desorption from the surface at this sample temperature.

 

115.    Y. Yamamoto, G. Bjork, A. Karlsson, H. Heitmann, and F. M. Matinaga

            "Quantum State Control In Semiconductor-Pn-Junctions.2. Controlled Spontaneous Emission In Quantum-Well Microcavity Lasers"

            Int. J. Mod. Phys. B 7 (8), 1653-1695 (1993).

 

            ABSTRACT: The principles and applications of controlled spontaneous emission in semiconductor microcavities are reviewed. The coupling efficiency of spontaneous emission into a lasing mode and the spontaneous emission rate can be modified by various microcavity structures. By increasing the coupling efficiency, semiconductor lasers with a very low threshold current, and semiconductors lasers and light emitting diodes with a high quantum efficiency, broad modulation bandwidth and low noise are expected.

 

116.    Y. Yamamoto, S. Inoue, W. Richardson, and S. Machida

            "Quantum State Control In Semiconductor-P-N Junctions.1. Squeezed State Generation In Semiconductor-Lasers"

            Int. J. Mod. Phys. B 7 (8), 1577-1652 (1993).

 

            ABSTRACT: Quantum statistical properties of laser light have been extensively studied for the last thirty years by using an operator Langevin equation, a density operator master equation, and a quantum mechanical Fokker-Planck equation. It has been generally accepted among physicists and quantum electronics engineers that an ideal laser operating at far above the threshold generates a coherent state of light. Various experimental facts such as the Poissonian photoelectron statistics, the shot noise limited photocurrent fluctuations, and the Gaussian distributions of optical homodyne detector output seem to support this. However, recent careful studies on a semiconductor laser have revealed that a semiconductor laser does not necessarily produce a coherent state of light, but generates a number-phase squeezed state, in which the photon-number noise is smaller than the standard quantum limit (shot noise limit or Poisson limit). This paper reviews the theoretical and experimental aspects of number-phase squeezed state generation by a semiconductor laser.

 

117.    Y. Yamamoto, F. Matinaga, S. Machida, A. Karlsson, J. Jacobson, G. Bjork, and T. Mukai

            "Quantum-Electrodynamic Effects In Semiconductor Microcavities - Microlasers And Coherent Exciton-Polariton Emission"

            J. Phys. IV 3 (C5), 39-46 (1993).

 

            ABSTRACT: We discuss the spontaneous emission of quantum well excitons in a monolithic microcavity. When the quantum well is excited by a nonresonant pump wave at high above the bandgap, the incoherent spontaneous emission is concentrated on the single resonant mode and the laser threshold is reduced by many orders of magnitude. When the quantum well exciton is excited by a resonant pump wave, the coherent spontaneous emission based on a ''microcavity exciton-polariton'' is observed. The spectral linewidth and the polarization of the pump wave are preserved and the coupling efficiency into the single resonant mode approaches 100%. The microcavity-induced normal mode splitting is observed in the frequency domain by photoexcitation spectrum measurements and in the time domain by pump-probe measurements.

 

118.    Y. Yamamoto and R. E. Slusher

            "Optical Processes In Microcavities"

            Phys. Today 46 (6), 66-73 (1993).

 

            ABSTRACT:

119.    Y. Yamauchi and N. Kobayashi

            "Low-Temperature Gaas Metalorganic Chemical Vapor-Deposition Using Dimethylamine Gallane And Arsine"

            Jpn. J. Appl. Phys. Part 2 - Lett. 32 (2A), L160-L163 (1993).

 

            ABSTRACT: Dimethylamine gallane (DMAG) is used for low-temperature GaAs metalorganic chemical vapor deposition (MOCVD) because it has a much lower decomposition onset temperature than trialkyl Ga sources. We grow GaAs layers using the simultaneous supply mode (conventional MOCVD) and an alternate supply mode (flow-rate modulation epitaxy-FME) for DMAG and arsine, and compare their electrical and optical properties. Mirror-like surfaces are obtained at substrate temperatures above 250-degrees-C, and low-temperature photoluminescence spectra show different excitonic features for both supply modes. For the simultaneous supply mode, an increase in arsine partial pressure during growth shifts the bound exciton peak to a longer wavelength due to the increase of the defect-related exciton peak. For the FME mode however, no peak shift is observed with increasing arsine partial pressure, indicating that defect incorporation is well suppressed in FME.

 

120.    Y. Yamauchi, K. Uwai, and N. Kobayashi

            "In-Situ Spectrum Observation Of Ga Deposition Process During Gaas Metal-Organic Chemical-Vapor-Deposition Using Surface Photoabsorption"

            Jpn. J. Appl. Phys. Part 2 - Lett. 32 (10A), L1380-L1382 (1993).

 

            ABSTRACT: In situ spectrum measurement by surface photo-absorption (SPA) is applied to study the Ga deposition process on (001) GaAs in metal-organic chemical vapor deposition (MOCVD). The change in SPA spectra is measured in the wavelength range from 300 nm to 800 nm, when triethylgallium is supplied on As-stabilized surface. The change at 470 nm is caused by the disappearance of the uppermost As dimer of c (4 x 4) surface followed by the appearance of a (2 x 4) As dimer domain or the formation of Ga-As back bonds. A broad spectrum from 500 nm to 800 nm is observed after one-monolayer Ga deposition, implying a correlation with Ga droplet formation. The calculated spectrum supports this broad spectrum being due to the photo-absorption by free Ga atoms on Ga-stabilized surface or metallic Ga atoms included in droplets.

 

121.    Y. Yamauchi, K. Uwai, and N. Kobayashi

            "Spectral Observation Of As-Stabilized Gaas-Surfaces In Metal-Organic Chemical-Vapor-Deposition Using Surface Photoabsorption"

            Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 32 (8), 3363-3369 (1993).

 

            ABSTRACT: The spectral dependencies of As-stabilized (001) GaAs surfaces in metal-organic chemical vapor deposition (MOCVD) are measured using the surface photo-absorption (SPA) method and compared them with those obtained in molecular beam epitaxy (MBE). The SPA spectrum of an As-stabilized surface at 600-degrees-C is anisotropic in regards to the perpendicularly intersecting incidence azimuths, [110] and [110BAR], of the monitoring light. It is also very similar at a arsine partial pressure of 4 Pa, which is a common MOCVD growth condition, to the spectrum obtained for an MBE As-surface having a c(4 x 4) reconstruction pattern in reflection high-energy electron diffraction (RHEED) observation, though not to the spectrum corresponding to a(2 x 4) pattern. Below 500-degrees-C, an isotropic signal appears and overlaps with the anisotropic spectrum of a c(4 x 4)-like surface, indicating that As species adsorbs excessively on a c(4 x 4)-like surface, which reduces its anisotropy. It is shown that by using different wavelengths, the dynamics of As desorption from each As-stabilized surface can be measured separately.

 

122.    T. Yanagawa, H. Nakano, Y. Ishida, and K. Kubodera

            "Alkaline Metal Dopants And Photodarkening In Colored Filter Glass"

            Appl. Phys. Lett. 62 (26), 3414-3416 (1993).

 

            ABSTRACT: It is clearly shown for the first time that alkaline metal ions assist the photodarkening effect in colored filter glass. Time responses of samples vary depending on the kind of alkaline metal dopants involved as additive compounds for improving glass quality. Energy relaxation times of photoexcited carriers after laser beam irradiation change following weight quotients of potassium oxides from sodium oxides. The fastest response after irradiation can be obtained when the quotient is approximately two. This quotient corresponds to compositions showing conspicuous mixed-alkali effects from potassium and sodium.

 

123.    T. Yanagawa, H. Nakano, Y. Ishida, and K. Kubodera

            "Host Glass Dependence Of Photodarkening In Colored Filter Glasses"

            Opt. Commun. 100 (1-4), 118-123 (1993).

 

            ABSTRACT: After photodarkening, colored filter glasses obtained from different glass makers show energy relaxation times that depend on dopant components in the glasses. Dopant analysis implies that potassium ions may affect the energy relaxation time shortening. In order to observe dopant dependence of the darkening, laser wavelengths are adjusted to the same absorption in all samples. CdSxSe1-x microcrystallite sizes in this report are confirmed not to affect the energy relaxation times.

 

124.    S. Yarlagadda and S. Kurihara

            "Fermi-Liquid Theory In The Low-Density 2-Dimensional Hubbard-Model"

            Phys. Rev. B 48 (14), 10567-10570 (1993).

 

            ABSTRACT: We examine the validity of Fermi-liquid theory in the low-density two-dimensional Hubbard model. Rom the ground-state energy we obtain the quasiparticle energy and the Landau interaction function. Then we prove that the quasiparticle-interaction function is finite and that the quasiparticle residue is nonzero for repulsive interactions. We also find, as a function of the excitation energy epsilon, that the quasiparticle lifetime approximately 1/epsilon2 ln epsilon. Hence, we conclude that Fermi-liquid theory holds in our model.

 

125.    S. Yarlagadda and S. Kurihara

            "Fermi-Liquid Theory In 2 Dimensions"

            Physica B 188, 971-974 (1993).

 

            ABSTRACT: We examine some of the issues concerning the validity of Fermi liquid theory in two dimensions. Contrary to previous claims, we find that the quasiparticle residue is nonzero and that the quasiparticle interaction function in the forward-scattering case is nondivergent for all values of the repulsive potential.