The thermal equilibrium concentrations of the various negatively charged Ga vacancy species were calculated. The triply negatively charged Ga vacancy, VGa3-, was studied in particular because it dominated Ga self-diffusion and Ga/Al interdiffusion under intrinsic and n-doping conditions, as well as the diffusion of Si donor atoms which occupied Ga sites. Under strong n-doping conditions, the thermal equilibrium VGa3- concentration was found to exhibit a temperature independence or a negative temperature dependence. That is, the concentration was unchanged, or increased, as the temperature was decreased. This was contrary to the normal point defect behavior, in which the point defect thermal equilibrium concentration decreased as the temperature was lowered. The observed behavior explained a number of known experimental results, and required either that VGa3- should attain its thermal equilibrium concentration at the onset of each experiment, or required the operation of mechanisms which involved point defect non-equilibrium phenomena.

T.Y.Tan, H.M.You, U.M.Gösele: Applied Physics A, 1993, 56[3], 249-58