R. Tsu

Tunneling in a finite superlattice

We have computed the transport properties of a finite superlattice from the tunneling point of view. The computed I‐V characteristic describes the experimental cases of a limited number of spatial periods or a relatively short electron mean free path.

Resonant tunneling in semiconductor double barriers

Resonant tunneling of electrons has been observed in double‐barrier structures having a thin GaAs sandwiched between two GaAlas barriers. The resonance manifests itself as peaks or humps in the tunneling current at voltages near the quasistationary states of the potential well. The structures have been fabricated by molecular beam epitaxy which produces extremely smooth films and interfaces.

A new semiconductor superlattice

We treat theoretically, through the use of Bloch functions, a new semiconductor superlattice where the interaction of the conduction band in one host material with the valence band of the other host material plays an important role. The result indicates that this superlattice offers new intriguing features, realizable with the In1−xGaxAs‐GaSb1−y Asy system. In addition, the tunneling probability is calculated across a barrier involving this system.

Electrical Transport Properties in a Superlattice

Boltzmanns equation is solved for electrons in a one‐dimensional superlattice under the influence of a uniform electric field; an energy independent scattering time and nonspherical energy bands are assumed. The current density‐electric field characteristic shows negative differential conductivity at fields of 103−104 V/cm independent of the detailed shape of the minibands.

Nonlinear Optical Response of Conduction Electrons in a Superlattice

The nonlinear optical response of conduction electrons in a one‐dimensional superlattice has been examined theoretically. Our results indicate that such structure may be a promising medium for nonlinear mixing of photons.

Laser‐induced recrystallization and damage in GaAs

We have investigated the recrystallization of ion‐implanted amorphous GaAs using a frequency‐doubled 10−8‐s pulsed Nd : YAG laser. The best results were obtained by spatially overlapping laser pulses at 20 MW/cm2. At power densities above 20 MW/cm2, not only does the GaAs surface begin to show uneven solidification, but also an increasing degree of disorder is revealed in Raman scattering and by a broad hump in the spectrum of channeled He‐ion backscattering. This laser‐induced damage is similar for single‐crystal and ion‐implanted GaAs samples. We attribute the damage at high power densities to the loss of arsenic and subsequent rapid cooling of a gallium‐rich liquid.

Vacancy Association of Defects in Annealed GaAs

Cathodoluminescence measurements were performed at 5 °K on GaAs annealed from 600 to 1100 °C under controlled arsenic vapor pressures. Various energy levels of defects were observed, and their association with Ga or As vacancies were determined from the pressure dependence. The defects associated with Ga vacancies were found to become increasingly important with increasing temperatures. Fast diffusing species such as copper can be ruled out as being responsible for the observed defects.

Profiling of periodic structures (GaAs–GaAlAs) by nuclear backscattering

In aiming at an electronic superlattice, epitaxial structures consisting of alternating layers of GaAs and GaAlAs have been grown by molecular‐beam evaporation. The technique of He‐ion backscattering provides a unique method for the direct and non‐destructive profiling of these structures for superlattice layers of a few hundred angstroms if detailed account is made of the backscattering process. The results of Raman spectroscopy and scanning electron microscopy are shown also to furnish complementary information on compositions and thicknesses, respectively. The three techniques give similar results.

A new mechanism for negative differential conductivity in superlattices

Abstract Electrons in a superlattice at high fields are suitably described in terms of localized states related to the potential wells. Conduction is dominated by transitions between adjacent wells if the potential drop over a superlattice period exceeds the width of the lowest miniband. It is shown that the probability of these transitions, and consequently the current as well, decrease with increasing field. This effect originates from decreasing overlap between electron states of neighbouring wells, and it is found for the interaction with acoustic phonons and with impurities as well.

Optical properties of semiconductor superlattice

Reflectivity measurements for a GaAs−AlAs superlattice and a Ga0.5Al0.5As alloy were performed. Analyses of these results permit the determination of both refractive indices and absorption coefficients. The absorption edges for the alloy and superlattice are approximately 2 and 1.63 eV, respectively. A shift of 0.11 eV from the absorption edge of GaAs compares favorably with transport measurements showing that the lowest energy state in such a superlattice is about 0.1 eV above the bottom of the conduction band of GaAs.