Behavior of electron-irradiation-induced defects in GaAs

In GaAs, electron irradiation is known to produce vacancy-interstitial pairs in the arsenic sublattice (${\mathit{V}}_{\mathrm{As}\mathrm{-}}$ ${\mathrm{As}}_{\mathit{i}}$). The associated levels are electron traps (labeled E1–E5), and hole traps (labeled H0 and H1). In addition, complexes (labeled H2–H5) involving the ${\mathrm{As}}_{\mathit{i}}$ and residual impurities are created in p-type GaAs. This different behavior between n- and p-type materials is found to be related to a difference in the mobility of ${\mathrm{As}}_{\mathit{i}}$ during the irradiation. The existence of the various levels observed for the ${\mathit{V}}_{\mathrm{As}}$-${\mathrm{As}}_{\mathit{i}}$ pair corresponds to a distribution in distance between ${\mathit{V}}_{\mathrm{As}}$ and ${\mathrm{As}}_{\mathit{i}}$. Most of the pairs are correlated in n-type material while in p-type material a large fraction of the pairs are uncorrelated. In order to verify this picture we have performed a study of the pair distribution versus the flux of irradiation in n- and p-type materials and versus the irradiation dose in p-type material. In p-type material, these studies confirm that the defect labeled H1 is a primary defect and the defects H2, H3, and H4 are complexes. The large diffusion length of ${\mathrm{As}}_{\mathit{i}}$ explains the observed creation rates and the annealing behaviors of these defects. In n-type material, a partial annealing of the defects E1–E5 is observed under high flux of irradiation because the mobility of ${\mathrm{As}}_{\mathit{i}}$ is then enhanced by the holes injected during the irradiation. Both this ionization-enhanced annealing and the thermal annealing (which occurs around 200 °C) can be understood in detail. A careful analysis of the kinetics of the pair annihilation and in particular the asymptotic behavior of these kinetics allows the determination of the fraction of correlated pairs and the evaluation to some extent of the distribution in distance of the pairs. Finally these conclusions allow us to propose a microscopic model for the defect E3, resulting from the interaction of ${\mathrm{As}}_{\mathit{i}}$ located at an average distance of 8 Å from the arsenic vacancy.