Experiments were performed on Zn diffusion at between 620 and 870C, using a dilute Ga-Zn source. The low Zn partial pressure established during annealing led to Zn surface concentrations of below 2 x 1019/cm3, and to the formation of characteristic S-shaped diffusion profiles. Accurate modeling of the Zn profiles, which were measured by means of secondary ion mass spectroscopy, showed that Zn diffusion under these doping conditions was mediated mainly by neutral and singly positively charged Ga interstitials via the kick-out mechanism. The temperature dependence of the individual contributions of neutral and positively charged Ga interstitials to Ga diffusion, for electronically intrinsic conditions, was determined. The data values were lower than the total Ga self-diffusion coefficient and were therefore consistent with the general interpretation that Ga diffusion under intrinsic conditions was mediated mainly by Ga vacancies. These results disproved the generally accepted interpretation of Zn diffusion in GaAs as occurring via doubly and triply positively charged Ga interstitials, and explained inconsistencies which were related to the electrical compensation of the acceptor dopant Zn by the multiply-charged Ga interstitials.

Zinc Diffusion in Gallium Arsenide and the Properties of Gallium Interstitials. H.Bracht, S.Brotzmann: Physical Review B, 2005, 71[11], 115216 (10pp)