ALCHEMI studies on the location of zinc in GaAs

Abstract

The diffusion of Zn in GaAs is anomalous in that the diffusion coefficient D is proportional to the Zn concentration squared. Further, the diffusion rate of the column III species in III-V layer structures (ie. Ga and Al in GaAs-GaAlAs) can be increased by 105 with the addition of doping levels of Zn3. The column V sites are not affected. As an aid to understanding the diffusion process we have located the position of the Zn in the GaAs lattice.There are four high symmetry positions in the zincblende structure that the Zn could occupy: Ga, As, T (Tetrahedral interstitial, located at 1/2 1/2 1/2 with four nearest neighbors at 0.433 a0) and H (Hexagonal interstitial, located at 5/8 5/8 5/8 with six nearest neighbors at 0.415 a0). Interstitial diffusion involves hopping between alternating T and H sites with the energy barrier to diffusion being equivalent to the difference in the potential energy of the two sites. Figure 1 indicates the possible low-index orientations for ALCHEMI studies which can differentiate between these sites.