DEFECT FORMATION DURING ZINC DIFFUSION INTO GAAS

The defect structure induced by zinc diffusion at 1170 K into undoped and indium-doped, semi-insulating GaAs single crystals was characterized for various diffusion times by analytical transmission electron microscopy of cross-sectional specimens. The results were compared with zinc concentration profiles obtained by spreading-resistance measurements on the same samples. Corresponding to zones of different zinc concentrations, three regions of characteristically different defect structures were distinguished. In the diffusion front region, interstitial-type dislocation loops, dislocation networks and gallium precipitates with voids in spatial correlation with the dislocations were found independent of diffusion conditions. The defect structure in the surface region depends on the diffusion conditions and is dominated by zinc-rich precipitates. For longer diffusion times, a transition region is observed where faceted voids and large vacancy-type dislocation loops coexist. A model for the formation of the diffusion-induced defects is presented which is based on the creation of a supersaturation of interstitial gallium atoms by the interstitial-substitutional zinc exchange and a resulting supersaturation of arsenic vacancies during diffusion.