Identification of the defect state associated with a gallium vacancy in GaAs andAlxGa1−xAs

Arguments based on new data as well as an analysis of the literature are given to show that the so-called $E3\mathrm{}$ radiation-damage defect state in GaAs and ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ is most likely a gallium vacancy. It is first shown that on the basis of chemical trends one should expect vacancies in GaAs to be stable at room temperature. It is then argued that most of the defects observed in room-temperature 1-MeV electron-irradiated GaAs are likely to be simply native defects rather than clusters or impurity complexes. Data on the orientation dependence of the defect production rate are given which show that the defects which recover at 500 K in GaAs are all due to Ga atom displacements. Finally, data are presented on the energy-level shifts of seven deep levels, including the $E3\mathrm{}$ level, in ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ as a function of Al mole fraction. These data show that the $E3\mathrm{}$ level is anomalous and remains fixed relative to the valence band whereas all other levels shift in energy to maintain their same relative position in the gap. This anomalous behavior is interpreted on the basis of theories of surface dangling bonds and vacancy states to be evidence that the $E3\mathrm{}$ level is a gallium vacancy.