PHOTOLUMINESCENCE STUDIES OF EXCITONIC TRANSITIONS IN GAN EPITAXIAL LAYERS

GaN epitaxial layers on sapphire substrates were grown by the rotating disk metal organic chemical vapor deposition technique. Excitonic tra nsitions from conduction band to spin-orbit split valence bands were o bserved. At 12 K we observed donor bound exciton and a very weak accep tor bound exciton. The temperature dependence of luminescence peak pos itions of free-excitons A and B were fitted to the Varshni's equation to study the variation of the band gap with temperature. The linewidth of the free exciton (A) was studied as a function of temperature and was explained by theoretical model considering the scattering of excit ons with acoustic phonons and longitudinal optical phonons. In the 12 K spectrum we also observed phonon-assisted excitonic transitions. The activation energy of the free exciton (A) was found to be 26 meV, whi le that of the donor bound exciton was 7 meV. The binding energy of th e donor was estimated as 35 meV and that of the acceptor as 250 meV. T he band gap of GaN was found to be 3.505 eV at 12 K and 3.437 at room temperature. All the parameters obtained in the present investigation are compared with those reported in the literature. (C) 1998 American Institute of Physics. [S0021-8979(98)05119-6].