Influence of silicon doping on vacancies and optical properties of Al_xGa_1-xN thin films

The authors have used positron annihilation spectroscopy and photoluminescence measurements to study the influence of silicon doping on vacancy formation in AlGaN:Si structures. The results show a correlation between the Doppler broadening measurements and the intensity from 510 nm photoluminescence transition. The reduction in the W parameter when the [Si]/[Al+Ga] fraction in the gas phase is above 3×10^-4 indicates that the positrons annihilate in an environment where less Ga 3d electrons are present, i.e., they are trapped in group-III vacancies. The observation of vacancies at these silicon concentrations coincides with the onset of the photoluminescence transition at 510 nm.