Impurity and self-diffusion mechanisms, and the nature of the associated point defects, were considered with regard to the Ga sub-lattice. Analyses of doping-enhanced AlAs/GaAs superlattice disordering data and impurity diffusion data led to the conclusion that, under thermal equilibrium and intrinsic conditions, the triply negatively-charged Ga vacancy (VGa3-) governed Ga self-diffusion and Al-Ga interdiffusion in As-rich crystals, while the doubly positively-charged Ga self-interstitial (IGa2+) predominated in Ga-rich crystals. With sufficient doping, VGa3- predominated in n-type crystals, while IGa2+ predominated in p-type crystals; regardless of the composition. The VGa3- species also contributed to the diffusion of the main donor species, Si, while IGa2+ also governed the diffusion of the main acceptor species, Zn and Be, via the kick-out mechanism. The thermal equilibrium concentration of VGa3- was found to exhibit a temperature independence, or even a small negative temperature dependence. That is, when the temperature was lowered, the equilibrium concentration of VGa3- was either unchanged or slightly increased. This behavior was consistent with many experimental results.

T.Y.Tan: Materials Chemistry and Physics, 1995, 40[4], 245-52