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.