Vacancy defects in photoexcited GaAs studied by positron two-dimensional angular correlation of annihilation radiation

The positron two-dimensional angular correlation of annihilation radiation (2D-ACAR) technique has been coupled with optical excitation to study the native point defects in semi-insulating GaAs. The As vacancy was observed below ∼170 K when illuminated with 1.41±0.07 eV photons. The temperature dependence of the 2D-ACAR spectra, with and without illumination, was studied. Data were also collected at 25 K as a function of the intensity of infrared light. The 2D-ACAR spectra reflect the ${\mathit{e}}^{+}$-${\mathit{e}}^{\mathrm{-}}$ pair momentum distribution at or near the vacancy and provides symmetry and electronic structure information, which can be used as a unique defect signature for the vacancy.