The electrical properties of GaAs single crystals were measured after annealing at various elevated temperatures in controlled atmospheres. Two types of defects were introduced as the result of annealing: (i) donors having a high concentration near the surface and (ii) acceptors having a lower surface concentration but extending further into the crystal. The As overpressure dependencies indicate that the donors are As vacancies and the acceptors are Ga vacancies since their respective concentrations are proportional to iPAs4minus;1/4and iPAs4+1/4. The entropy and enthalpy changes for the vacancy formation reactions at the surface were evaluated, based on experimental data and thermodynamic analysis. The diffusion coefficients of vacancies follow the relationsD(VGa) =2.1times;10minus;3thinsp;exp(minus;2.1/kT) andD(VAs) =7.9times;103thinsp;exp(minus;4.0/kT). Both types of vacancies form nonradiative centers as determined from photoluminescence experiments.
展开▼
