Low-temperature (1.7 to 20K) photoluminescence and reflectance methods were used to investigate free and bound exciton, and shallow impurity, states. A 300μm-thick nitride layer, grown via hydride vapor-phase epitaxy onto sapphire (00•1), and with an exceptionally low (3 x 106/cm2) dislocation density was used to obtain very high quality spectra. Both free and bound n = 2 excitons were identified, thus confirming that the A free exciton binding energy was about 0.0264eV; regardless of strain. Principal neutral donor-bound exciton peaks involving 2 to 3 different donors were resolved, as were 2-electron satellites which involved up to 5 different residual donors with binding energies ranging from 0.022 to 0.0345eV.

Low-Temperature Luminescence of Exciton and Defect States in Heteroepitaxial GaN Grown by Hydride Vapor Phase Epitaxy. B.J.Skromme, J.Jayapalan, R.P.Vaudo, V.M.Phanse: Applied Physics Letters, 1999, 74[16], 2358-60