TEMPERATURE-DEPENDENT OPTICAL BAND-GAP OF THE METASTABLE ZINCBLENDE STRUCTURE BETA-GAN

The temperature-dependent (10-300 K) optical band gap E(0)(T) of the epitaxial metastable zincblende-structure beta-GaN(001)4X1 has been determined by modulated photoreflectance and used to interpret low-temperature photoluminescence spectra. E(0) in beta-GaN was found to vary from 3.302+/-0.004 eV at 10 K to 3.231+/-0.008 eV at 300 K with a temperature dependence given by E(0)(T) = 3.302-6.697 X 10(-4)T(2)/(T+600) eV. The spin-orbit splitting Delta(0) in the valence band was determined to be 17+/-1 meV. The oscillations in the photoreflectance spectra were very sharp with;a broadening parameter Gamma of only 10 meV at 10 K. The dominant transition observed in temperature-dependent photoluminescence was attributed to radiative recombination between a shallow donor, at congruent to 11 meV below the conduction-band edge and the valence band.