Overview of Quantum Physics and Electronics
Research
Naoshi Uesugi
Physical Science Laboratory
Our research in the fields of quantum physics
and electronics, which is based on ultra-small
semiconductor structures fabricated by high-quality
semiconductor crystal growth and advanced
device fabrication techniques, focuses on
single-electron control, new electron transport
mechanisms and wide-bandgap semiconductor
physics. Our aim is the development of innovative
semiconductor devices. The Quantum Solid
State Physics Research Group and the Wide-Bandgap
Semiconductor Research Group are working
in the following areas.
Quantum Solid State Physics Research Group
(1) Electronic properties of low-dimensional
semiconductor heterostructures (two dimensional
carrier transport and correlation effects
in high-mobility semiconductors, carrier
interactions in bilayer (electron-electron
and electron-hole) systems, and cyclotron
resonance in low-dimensional semiconductors).
(2) Single-electron control in quantum dot
systems (electronic properties of semiconductor
artificial atoms and molecules, control of
electronic states in coupled quantum dots
by electromagnetic waves and magnetic fields,
and fundamental properties of solid-state
quantum computers using artificial molecules).
(3) Controlled semiconductor-surface crystal
growth and nano-scale evaluation (heterostructure
growth mode on high-index crystal surfaces
and its application to novel electronic devices,
and direct nano-scale observation of electronic
states by low-temperature scanning-tunneling-microscopy
(STM) technique).
Wide-Bandgap Semiconductor Research Group
(1) High-quality GaN crystal growth (mechanism
of GaN crystal growth by MOCVD, high-concentration
p-type doping, and device processing technology).
(2) Facet growth (GaN facet growth mechanism,
InP compound semiconductor facet growth mechanism,
and their applications for surface-emitting
devices).
(3) GaN semiconductor device physics (electronic
and optical properties of GaN quantum well
structures, high-temperature electron devices,
and short-wavelength light emitting devices).
(4) Crystal growth under low gravity (high
quality InGaAs compound crystal growth in
low gravity).
Major results obtained this fiscal year 1999
are reported in the following pages. We fabricated
two-dimensional electron bilayer systems
using high-quality double-quantum-well structures
and experimentally demonstrated that the
magnetoresistance exhibits a periodic structure
when the electron densities in the two layers
are varied independently. This periodic pattern
reflects how the electrons occupy the orbits
of the quantum-mechanically-coupled bilayer
system, which may lead to "quantum correlated
electronics" where the correlation between
carriers in semiconductors is actively utilized.
By the combination of atomically-flat epitaxial
growth technique and suppression of strong
internal electrical field inherent to nitride
materials, we were able to fabricate an AlGaN
quantum-well light emitting diode with an
emission wavelength of 346 nm - the shortest
wavelength to date from nitride materials
-under cw current injection at room temperature.
This achievement is an important step in
the realization of an ultra-violet laser
diode.
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