Influence of Si and S doping on structural defects in LEC-grown gallium arsenide

Abstract

The influence of Si and S doping on the reduction of the dislocation density in <111>LEC-grown GaAs crystals is re-evaluated by means of selective DSL photoetching. Based on the ability of the DSL technique to discriminate between grown-in and stress-induced dislocations new arguments are presented on the controversial mechanism of the reduction of the dislocation density by impurities. It is concluded that S-doping above a critical carrier concentration of 1 x 1018 cm-3 results in solution and dispersion hardening (i.e. the critical resolved shear stress is increased), while in heavily Si-doped GaAs no hardening occurs but dislocation generation is prevented by the elimination of nucleation sites formed by intrinsic point defects, presumably Asi. Si-doped GaAs crystals appear to be advantageous over S-doped GaAs crystals because apart from the overall reduced dislocation density, microdefect-free GaAs crystals can be obtained with carrier concentrations up to 6 x 1018 cm-3, while heavily S-doped ingots contain a high density of microdefects presumably faulted arsenic interstitial loops and/or small Ga-S precipitates.