We present a comprehensive study of epitaxially grown and As-coated GaAs(100) surfaces as a function of As desorption temperature and background pressure. We have used low-energy electron diffraction to determine surface reconstruction, and core-level and valence-band soft-x-ray photoemission spectroscopy to perform chemical and electronic characterization of these surfaces. We find gradual changes in surface geometry and composition, and a limited (-120 meV) Fermi-level movement over numerous reconstructions in the 250-650'C annealing temperature range. The surface ionization potential and work function exhibit large changes between different surface reconstructions. In conjunction with other techniques, work-function measurements present evidence of surface inhomogeneity for many of the desorption temperatures and surface reconstructions. This inhomogeneity appears related to the existence of differently reconstructed patches on the surface. Our results emphasize the complexity of reconstructed GaAs(100) surfaces and the advantages of a multiple-technique approach for their characterization.

We report results from a statistical analysis of avalanches of cohesive powders in a slowly rotated drum. Interparticle adhesion, which diminishes the effect of inertia and whose magnitude strongly fluctuates in a local scale, makes avalanches in slightly cohesive powders eligible for displaying self-organized criticality. However, the results show that avalanche sizes, time interval between avalanches, and maximum stable angle do not follow a power-law distribution. Otherwise, these parameters scale with powder cohesiveness.

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We have used cathodoluminescence (CL) and photoluminescence spectroscopy to observe deep-level states in GaAs grown at low-substrate temperatures by molecular beam epitaxy (LT GaAs) and the evolution of these states upon annealing. The as-grown material shows intense deep-level emissions which can be associated with an excess concentration of arsenic, mostly present as As-antisite and As-interstitial defects. These emissions subside with annealing for a few minutes at temperatures above 450 °C. CL measurements clearly show a dramatically reduced concentration of traps in the post-growth 600 °C annealed material. Additional measurements carried out on As/GaAs systems indicate a high surface-recombination velocity for these interfaces. These results account for a diminished role of electronic point defects in controlling the insulative behavior of LT GaAs and strongly supports a ‘‘buried’’ Schottky barrier model, which involves ultrafast recombination of carriers at surfaces of embedded arsenic clusters formed during the annealing processing of LT GaAs.

Inhomogeneous and wide range of barrier heights at metal/molecularbeam epitaxy GaAs(100) interfaces observed with electrical measurements Lowtemperature GaAs epitaxial growth using electroncyclotron resonance/metalorganicmolecularbeam epitaxy We report soft x-ray photoemission studies of metal/molecular-beam epitaxy (MBE)-GaAs(lOO) interfaces formed at low temperature. Our results indicate that rectifying barrier heights are proportional to the metal work function in accordance with Schottky's original description of metal-semiconductor contacts. These results confirm the predictions of a selfconsistent model of metal-semiconductor interfaces, and suggest that metal-induced gap states and native defect mechanisms are not major factors in determining the Fermi level energy at "ideal" interfaces. We attribute deviations from the ideal Schottky limit behavior observed for interfaces formed at room temperature to metallization-induced atomic relaxations (rather than electronic relaxations) occurring at metal-semiconductor contacts. We present a useful methodology for analyzing electronic properties at metal-semiconductor interfaces. The pronounced differences in barrier height formation between MBE vs melt-grown GaAs can evidence the role of deep states in controlling Schottky barriers at metal/melt-grown GaAs.