Deep-level transient Fourier spectroscopic, Hall-effect and DSL etching techniques were used to analyze initially semi-insulating bulk samples after annealing at temperatures of between 800 and 1100C under As pressures of between 0 and 3bar. It was found that the electrical resistivity, electronic mobility and EL2 concentration increased with increasing As pressure at all temperatures. Initially n-type samples were converted to p-type at pressures below 0.5bar and temperatures above 1000C. It was noted that As precipitates disappeared at high temperatures, and reappeared during low temperature annealing. In order to explain the observations, it was proposed that long-range rapid As interstitial transport occurred between the surface and the bulk, together with short-range Ga vacancy migration involving dislocations as sources and sinks. It was suggested that a discrepancy, with regard to very small reported tracer diffusion coefficients, could be resolved by assuming that rapidly diffusing marked interstitials which entered the lattice at the crystal surface tended to exchange sites with unmarked lattice species. They then became immobile.

M.Noack, K.W.Kehr, H.Wenzl: Journal of Crystal Growth, 1997, 178, 438-44