Fast interstitial diffusion in As-pressure annealed GaAs

Abstract

Abstract Electronic properties and microstructure of bulk GaAs crystals can be varied over a large range by thermal annealing at different As-gas pressures. Deep-level transient Fourier spectroscopy, Hall effect and DSL etching have been applied to analyse originally semi-insulating GaAs bulk samples after annealing between 800 and 1100°C at As-pressures between 0 and 3 bar. The electrical resistivity, electronic mobility and the EL2 concentrations increased with increasing As-pressure at all temperatures although at levels differing by orders of magnitude. Initially n-type samples are converted to p-type at pressures below 0.5 bar and temperatures above 1000°C. Published results of the Oda-group could be confirmed. As-precipitates disappear at high temperature and reappear at low-temperature annealing. We propose long-range and fast As-interstitial transport between surface and bulk combined with short-range Ga-vacancy migration with dislocations as sources and sinks as elementary processes to explain the observations. The discrepancy with the very small literature values of tracer diffusion coefficients can be resolved by assuming that rapidly diffusing marked interstitials which enter the lattice at the crystal surface tend to exchange sites with unmarked lattice species after which they are immobilized.