Secondary ion mass spectroscopy and photoluminescence studies were made of VGa during Zn diffusion into Si-doped material. Photoluminescence spectra were obtained at various etching depths below the sample surface. After annealing the samples in excess As4 vapor at 650C, the conversion of n-type material into p-type material was observed by making electrical measurements in the region near to the sample surface. The importance of the SiGa-VGa emission band in photoluminescence spectra from thermally converted regions indicated that VGa which were generated at the surface during annealing were responsible for the thermal conversion. The results also showed that the main point defects which were generated during annealing under Ga-rich conditions were VAs and GaAs. In the case of Zn-diffused Si-doped substrates at 600C, the disappearance of the VGa-related band from the photoluminescence spectra of diffused regions furnished evidence for the incorporation of Zn interstitials into Ga sites during diffusion. An accumulation of VGa was found ahead of the Zn diffusion front. The Zn-diffused samples were also annealed at 800C for 2h in vacuum, or in As4 vapor with or without a Si3N4 cap. In the case of samples which were annealed in vacuum, an abrupt diffusion front advanced slightly into the bulk; with a supersaturation of VGa ahead of the front. On the other hand, samples which were annealed in As vapor, with or without a cap on the surface, exhibited double Zn concentration profiles with an undersaturation of VGa around the tail region. These results revealed the important role which was played by non-equilibrium point defects, and were explained in terms of a kick-out mechanism for Zn diffusion.

Reactions of Gallium Vacancies during Annealing and Zn Diffusion in GaAs: Si. N.H.Ky, J.D.Ganière, F.K.Reinhart, B.Blanchard: Materials Science Forum, 1994, 143-147, 1397-402

Table 10

Diffusivity of Zn in GaAs