Si-defect concentrations in heavily Si-doped GaAs: Changes induced by annealing

Previously reported annealing effects on the carrier density and free-carrier absorption are correlated with photoluminescence and localized vibrational mode infrared absorption measurements of annealed samples of heavily doped GaAs: Si. Annealing in the range 400≤TA≤750 °C produces the following qualitative changes: (i) a major reduction in the free-carrier concentration ne, (ii) an increase in the carrier absorption cross section, (iii) a reduction of the SiGa localized mode absorption band, and (iv) the introduction of a new photoluminescence band at 0.98 eV. A defect model is proposed which is consistent with the observed changes. There is a major reduction in [SiGa], the Si donor concentration, which is a function of the anneal temperature between 400 and 750 °C. The reduction is probably through the formation of (SiGa − VGa) pairs. There is little change if any in [SiAs] the Si acceptor concentration. When TA = 400°C the ne = [SiGa] −[SiAs]. When TA = 600 and 750°C, a new acceptor is formed having concentrations ≃3 to 4×1018 cm−3, in samples having [Si]≃4×1019 cm−3, and ne≠[SiGa] − [SiAs]. The new acceptor defect is a Si complex with an acceptor state ≃0.54 eV above the valence band. There is no evidence for SiGa → SiAs site transfer after annealing at any TA in the 400–750°C range. Annealing at 1100 °C removes all the lower-temperature annealing effects including the new acceptors and again ne =[SiGa] − [SiAs].