TEMPERATURE-DEPENDENCE OF EXCITONIC PHOTOLUMINESCENCE AND RESIDUAL SHALLOW DONORS IN HIGH-PURITY GAN AL2O3/

The temperature dependence of free and bound exciton lines in high-pur ity, undoped wurtzite GaN layers has been studied by photoluminescence (PL) between 2 and 300 K. Below 30 K the neutral donor bound exciton D degrees X produces the strongest near band gay PL signal whereas fre e A and B excitons dominate the spectrum at room temperature. A deconv olution of the asymmetric D degrees X line shape provides strong evide nce for two residual shallow donors differing in ionisation energies b y a factor of 1.5. The origin of a PL line occurring at E-g = 116 meV is discussed in two alternative models. (C) 1997 Elsevier Science S.A.