D. S. Katzer

Homogeneous Linewidths in the Optical Spectrum of a Single Gallium Arsenide Quantum Dot

The homogeneous linewidths in the photoluminescence excitation spectrum of a single, naturally formed gallium arsenide (GaAs) quantum dot have been measured with high spatial and spectral resolution. The energies and linewidths of the homogeneous spectrum provide a new perspective on the dephasing dynamics of the exciton in a quantum-confined, solid-state system. The origins of the linewidths are discussed in terms of the dynamics of the exciton in zero dimensions, in particular, in terms of lifetime broadening through the emission or absorption of phonons and photons.

Low-temperature spin relaxation in n-type GaAs

on GaAs. Basic facts and a considerable body of ex-perimental and theoretical results related to bulk Group III-Vsemiconductors are collected in Ref. 5. Later on, much newinformation concerning mainly low-dimensional structureshas been obtained. Nevertheless, there remain gaps in thisknowledge that have become visible with the emerging of anapplication-directed angle on spin-related phenomena~spintronics!.

Excited state spectroscopy of excitons in single quantum dots

We describe the results of a photoluminescence study of quantum dots which are formed by interface fluctuations in narrow GaAs/AlAs single quantum wells. The photoluminescence measurements were made with lateral spatial resolution ranging from the macroscopic down to the optical near‐field regime. For spatial resolution below a few square microns the photoluminescence from individual quantum dots is resolved. Photoluminescence excitation spectroscopy is used to study the excited state spectrum of an exciton bound in a single quantum dot.

Current collapse induced in AlGaN/GaN high-electron-mobility transistors by bias stress

Current collapse is observed to be induced in AlGaN/GaN high-electron-mobility transistors as a result of short-term bias stress. This effect was seen in devices grown by both metalorganic chemical vapor deposition (MOCVD) and molecular-beam epitaxy (MBE). The induced collapse appears to be permanent and can be reversed by SiN passivation. The traps responsible for the collapse have been studied by photoionization spectroscopy. For the MOCVD-grown devices, the same traps cause the collapse in both unstressed and stressed devices. These effects are thought to result from hot-carrier damage during stress.

Intrinsic multiple quantum well spatial light modulators

Large improvements are reported in the sensitivity of optically addressed multiple quantum well spatial light modulators. In prior work with these materials the quantum well region has been made semi‐insulating. It is shown that this is unnecessary and in fact detrimental to performance. By placing layers containing high trap concentrations at the ends of the structure and leaving the active quantum well layers intrinsic the speed of the device at a given illumination is improved by more than four times, diffraction efficiency is enhanced and spatial resolution is almost the same.

Reduction of buffer layer conduction near plasma-assisted molecular-beam epitaxy grown GaN/AlN interfaces by beryllium doping

Beryllium doping of epitaxial GaN layers is used to reduce leakage currents through interfacial or buffer conducting layers grown by plasma-assisted molecular-beam epitaxy on SiC. Capacitance–voltage measurements of Schottky barrier test structures and dc pinch-off characteristics of unintentionally doped GaN high-electron-mobility transistors indicate that these leakage currents are localized near the GaN/AlN interface of our AlGaN/GaN/AlN device structures. Insertion of a 2000 A Be:GaN layer at the interface reduces these currents by three orders of magnitude.

Manipulation of the Spin Memory of Electrons in n-GaAs

We report on the optical manipulation of the electron spin relaxation time in a GaAs-based heterostructure. Experimental and theoretical study shows that the average electron spin relaxes through hyperfine interaction with the lattice nuclei, and that the rate can be controlled by electron-electron interactions. This time has been changed from 300 ns down to 5 ns by variation of the laser frequency. This modification originates in the optically induced depletion of an n-GaAs layer.

Interfaces in GaAs/AlAs quantum well structures

We present a study of the bottom interface (GaAs on AlAs) in GaAs/AlAs single quantum wells using reflection high‐energy electron diffraction, luminescence, and luminescence excitation spectroscopy. The results indicate that it is possible to grow GaAs/AlAs quantum wells with two truly smooth interfaces using molecular beam epitaxy with growth interrupts. A set of samples in which the growth interrupt time on the bottom interface was changed illustrates in a systematic way the qualitative behavior possible in luminescence spectra. In particular, the energy splitting between the exciton peaks is observed to vary in the rough regime and in the truly smooth regime, although in a different way.

Measurement of relaxation between polarization eigenstates in single quantum dots

Low temperature relaxation of excitons between polarization eigenstates in single interface fluctuation quantum dots is studied using copolarized and cross-polarized transient differential transmission spectroscopy. The measured spin relaxation times are on the order of ∼100 ps. Such a spin relaxation time is longer than the reported times for thin quantum wells, but considerably shorter than the predicted times for interface fluctuation quantum dots.

High‐resolution spatial light modulators using GaAs/AlGaAs multiple quantum wells

We report improved performance in semi‐insulating GaAs/AlGaAs quantum well based spatial light modulators grown by molecular beam epitaxy. The optically addressed modulator reported here are of a new design and have significantly higher spatial resolution than previously reported devices. Strong diffraction efficiencies are described for spatial periods as fine as 2.6 μm at framing rate as high as 600 kHz. Two modulators are characterized, one with x=0.1 and the other with x=0.3 for the AlxGa1−xAs quantum barriers of the superlattices.