Optical properties of residual shallow donors in GaN epitaxial layers grown by horizontal LP-MOCVD

Photoluminescence (PL) properties of the residual shallow donors in GaN epitaxial layers grown by low-pressure metal organic chemical vapor deposition (LP-MOCVD) were reported. Well-resolved free exciton transitions and luminescence due to the residual shallow donors were observed. The localization energy and binding energy of the neutral shallow donor were found to be 7 meV and 35 meV, respectively. In addition we identified a new ionized donor bound exciton center. Temperature dependence of the neutral donor bound exciton PL peak was found to follow the same variation as the band gap with temperature and Varshni's coefficients were obtained. The linewidth of donor bound exciton transition increases linearly with temperature and their interaction with the acoustic phonons was thought to be the only contribution to the linewidth. From the PL intensities the thermal activation energy of the neutral donor bound exciton was estimated as 9 meV. The ratio of the total free excitons' intensity to the total bound excitons' intensity increases with temperature, which shows that the donor bound excitons thermally dissociate releasing free excitons.