Si-defect concentrations in heavily Si-DOPED GaAs: annealing-Induced changes-II

Isothermal annealing produces changes in the free carrier density, defect-induced localized vibrational mode (LVM) infrared absorption, microstructure as measured by transmission electron microscopy (TEM), and critical resolve shear stress of heavily Si-doped GaAs. The changes have been measured and correlated for three different Si concentrations for several annealing temperatures. The measurements reveal temperature dependent annealing-induced changes in several specific defect concentrations. The observations indicate the following behavior for two ingots with Si] ≳ 2 × 10¹⁹ cm⁻¹³: (1) when the anneal temperature, T_A = 400°C, the concentration of Si_ga donors, as determined from LVM spectra decreases probably due to the generation of V_Ga defects followed by the formation of Si_Ga-V_Ga pairs. This change is responsible for observed decreases in carrier density and the large increase in yield stress. The yield stress shows a dependence of the form σ-σ_o ∝ Si_Ga-V_Ga]^1/4. (2) When T_A = 500°C, the LVM spectra indicate that all of the observed Si defect concentrations change. The decrease in Si_Ga] alone cannot explain the decrease in carrier density, and a previous suggestion that a new acceptor is required is confirmed. Both the LVM measurements and the shear stress indicate that only a small fraction of the Si_Ga] reduction is by the formation of Si_Ga-V_Ga pairs. (3) When T_A = 700°C, a new acceptor is still required and the other experimental observations at T_A = 500°C are also still seen here. There is a large decrease in Si_Ga] and Si_As] observed for short anneal times which coincides with the formation of Si-rich extrinsic loops and the loop area/vol increases with Si]. (4) When T_A > 700°C, all of the changes become smaller as T_A increases. For lower Si] ~ 1.5 × 10¹⁸ cm⁻³, no significant annealing-induced changes are observed for any of the T_A given above.