Direct determination of the silicon donor ionization energy in homoepitaxial AlN from photoluminescence two-electron transitions

Abstract

We report on the identification of a two-electron transition for the shallow donor silicon in homoepitaxial AlN. One c-oriented sample was analyzed by low temperature PL spectroscopy on multiple excitation spots. We find a unique correlation of one single emission band, 76.6 meV below the free excitonic emission with the luminescence of excitons bound to neutral silicon proving the identity as a two-electron transition. The assignment is confirmed by temperature dependent PL investigations. We find a donor ionization energy of 63.5 +/- 1.5 meV for silicon in AlN. Beyond, based on our experimental results, we comment on the discussion about the role of silicon impurities in wurtzite AlN supporting the approach that silicon forms a DX center with the DX-ground state lying closely below the neutral donor state.