Photoquenching effect and thermal recovery process for midgap levels in GaAs: An<i>EL</i>2 family in GaAs

Abstract

We have studied the photocapacitance quenching effect and the thermal recovery process for the EL2 family in heat-treated GaAs. During the heat treatment at 850 \ifmmode^\circ\else\textdegree\fi{}C with use of an infrared rapid thermal process, it was identified that EL2, as the main midgap-level defect in GaAs, does not exist alone, but three different midgap levels at 0.73, 0.81, and 0.87 eV below the conduction band coexist with it as a family in various proportions. The EL2 out-diffusion coefficient of 1.02\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ ${\mathrm{cm}}^{2}$/s indicates that EL2 should have a contribution from an interstitial arsenic atom (${\mathrm{As}}_{\mathrm{i}}$). These three midgap levels represent a nonexponential quenching transient at 77 K and three activation energies (150, 300, and 350 meV) of the thermal recovery process. Our data indicate that three midgap levels in GaAs make up the EL2 family, each involving a different metastable state. We suggest that three kinds of EL2 could each have their own metastable states and coexist as a family. We conclude that, if EL2 has the atomic structure of ${\mathrm{As}}_{\mathrm{Ga}+\mathrm{X}}$, X might be an interstitial arsenic atom (${\mathrm{As}}_{\mathrm{i}}$) or a vacancy complex with ${\mathrm{As}}_{\mathrm{i}}$..AE