Are the Models of the Triply Charged Gallium Vacancy and Doubly Charged Gallium Interstitial Alive or Dead

We have found that the measured diffusivity can be quite different than predicted by recent models of multiply-charged defects. Key problems dealing with the measurement and the interpretation of diffusion mechanisms are discussed. Using a few common variations in GaAs epilayer growth, we have obtained diffusivities which range over several orders of magnitude at the same temperature. Making use of the relatively weak In-As bond, we have used In as a marker to measure group III interdiffusion, DIII. DIII is consistent with the results of others using Al as a marker in n-type GaAs, but orders of magnitude smaller than predicted by the triply charged Ga vacancy, V3−Ga, model of Tan and Gosele. Although diffusion can be attributed to a negatively charged vacancy in n-type GaAs, In is found to often move by a kick-out mechanism in p-type GaAs. It appears likely that many early experiments with n- and p-type GaAs-AlAs interdiffusion were affected by large concentrations of Ga interstitials, IGa, caused by Fermi energy pinning at the growing surface. We present the first direct experimental evidence for the existence of a positively charged Ga interstitial. Our results, combined with those of others, suggest that VGa has a single negative charge associated with it. Because epilayer growth conditions appear to cause the point defect concentrations to deviate substantially from equilibrium, we conclude that the exact charge states of VGa and IGa still remain to be determined.