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

Abstract

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≤T_A≤750 °C produces the following qualitative changes: (i) a major reduction in the free‐carrier concentration n_e, (ii) an increase in the carrier absorption cross section, (iii) a reduction of the Si_Ga 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 [Si_Ga], 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 (Si_Ga − V_Ga) pairs. There is little change if any in [Si_As] the Si acceptor concentration. When T_A = 400°C the n_e = [Si_Ga] −[Si_As]. When T_A = 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 n_e≠[Si_Ga] − [Si_As]. The new acceptor defect is a Si complex with an acceptor state ≃0.54 eV above the valence band. There is no evidence for Si_Ga → Si_As site transfer after annealing at any T_A in the 400–750°C range. Annealing at 1100 °C removes all the lower‐temperature annealing effects including the new acceptors and again n_e =[Si_Ga] − [Si_As].