Simulation of the transient indiffusion-segregation process of triply negatively charged Ga vacancies in GaAs and AlAs/GaAs superlattices

Abstract

In GaAs and AlAs/GaAs superlattice crystals containing n-type regions, several sets of recent experimental results obtained from diffusion studies require the interpretation that the responsible point defect species, the triply negatively charged Ga vacancy (VGa3−), has attained its thermal equilibrium concentration (CVGa3−eq) at the onset of an experiment. This could be due to either the fact that under heavy n-doping conditions CVGa3−eq is fairly temperature independent, or the fact that the transient process of populating VGa3− from an undersaturated to the appropriate CVGa3−eq value via indiffusion from the surfaces to the interior of the crystals is extremely rapid. We have simulated the transient process of populating VGa3− to the crystal interior. The experiments use crystals consisting of adjacent intrinsic and n-type regions for which CVGa3−eq values are different, leading to the simultaneous occurrence of VGa3− diffusion and segregation phenomena. A diffusion-segregation equation has been derived and subsequently used in the simulation calculations. The simulation results showed that, as long as n-type regions are involved, such transient processes are ineffective and therefore cannot explain the experimental requirement that VGa3− is already present in the appropriate CVGa3−eq(n) value at the onset of an experiment. On the other hand, the transient process is sufficiently rapid for the purely intrinsic crystal cases. These simulation results support our recent finding that the CVGa3−eq(n) values are essentially temperature independent, obtained via a thermodynamic treatment.