Enhanced and retarded Ga self-diffusion in Si and Be doped GaAs isotope heterostructures

Ga self-diffusion in undoped, Si- and Be-doped (GaAs)-Ga-71/(GaAs)-Ga-nat isotope heterostructures has been investigated at temperatures between 736 degrees C and 1050 degrees C. Concentration profiles of the Ga isotopes measured separately by secondary ion mass spectrometry reveal retarded (enhanced) self-diffusion when doped p-type (n-type), compared to intrinsic conditions. Electrochemical C-V profiling was performed to determine the free carrier concentrations before and after annealing. Detailed analysis of the doping dependence of Ga self-diffusion includes a compensation of Si donors by negatively charged vacancies and shows that one native defect, presumably the vacancy on the Ga sublattice, in the neutral, singly and doubly negatively charged states governs the self-diffusion process. The energy levels E-V- - E-v = 0.42 eV and E-V2- - E-v = 0.60 eV of the singly and doubly negatively charged gallium vacancy have been deduced from the doping dependence of Ga self-diffusion. No significant contribution from the triply negatively charged Ga vacancy has been found. Our evaluation of the doping dependence of Ga self-diffusion is compared with literature data for the group-III atom diffusion in the AlGaAs material system. Seemingly inconsistent literature data can now be described consistently on the basis of our results. Finally, thermal equilibrium concentrations and transport coefficients of Ga vacancies in GaAs in their various charge states are calculated for different doping conditions taking into account the vacancy related energy levels and the thermal equilibrium concentration of neutral vacancies which were deduced from our self-diffusion data. (C) 1999 Elsevier Science Ltd. All rights reserved.