Diffusion mechanisms and superlattice disordering in GaAs
This paper reports recent progress in our understanding of mechanisms of gallium self-diffusion, of impurity diffusion, and of doping-enhanced superlattice disordering in GaAs. An analysis of the available results of Ga-Al interdiffusion in GaAs/AlAs superlattices allows us to conclude that gallium self-diffusion in GaAs is carried by triply negatively charged gallium vacancies under intrinsic and n-doping conditions. The mechanism of the enhanced superlattice disordering due to silicon doping is the Fermi-level effect which increases the concentrations of the charged point-defect species. For the effect of the p dopants beryllium and zinc, the Fermi-level effect has to be considered together with dopant diffusion-induced gallium self-interstitial supersaturation or undersaturation. The self-diffusion of gallium in GaAs under heavy p-doping conditions is governed by positively charged gallium self-interstitials. Consistent with their effect on superlattice disordering, zinc and beryllium diffusion appears to be governed by the kick-out mechanism. The diffusion of silicon appears to be governed by gallium vacancies and the existing silicon pair diffusion model seems satisfactory. In agreement with the gallium self-diffusion mechanism, however, an alternative model has been proposed. Dislocations in GaAs and in other III-V compounds are found to be point-defect sinks and/or sources with only a limited efficiency. Clean experiments are proposed allowing the relation of each result with the effect of only one pre-selected experimental parameter. It is expected that these experiments will yield results which will serve to confirm some of the present findings, to indicate necessary modifications for others, and to unravel phenomena and understanding in previously unexplored areas. © 1988.
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