Diffusion and native defects in GaAs

Native defects, i.e., vacancies and interstitials, are responsible for controlling the diffusion of atoms in GaAs. Three classes of experimental design are available to probe native defects: equilibrium, weak nonequilibrium, and strong nonequilibrium. The necessary and sufficient conditions required to define and quickly bring the native defect concentrations to their equilibrium values are discussed. Experimental results are presented which show that native defect equilibrium can be approximated in practice, and used to determine that interdiffusion of either Al or In occurs via a Ga vacancy, with a charge of -1, in both n- and p-type GaAs. Strong nonequilibrium which applies when substantial mass transfer occurs, is of little help in understanding diffusion. Weak nonequilibrium corresponds to a perturbation in the equilibrium concentration of one native defect. Such experiments have been used to show that positively charged Zn and Ga interstitials are the first defects in the crystal to equilibrate with the ambient vapor