PHOTOLUMINESCENCE AND REFLECTANCE STUDIES OF EXCITON-TRANSITIONS IN WURTZITE GAN UNDER PRESSURE

We have measured photoluminescence (PL) and reflectance spectra of hig h-quality wurtzite GaN on sapphire at pressures up to 8 Cpa (T=10 K). All three intrinsic exciton transitions arising from the A, B, and C i nterband transitions were observed in reflectance measurements. The PL spectra are dominated by the A and B free exciton transitions and the recombination of an exciton bound to a neutral donor. Transitions due to the excited n=2 state of the A exciton and the first- and second-o rder LO phonon replicas of the A free exciton were also resolved. The pressure dependence of the A band gap and exciton binding energy is ob tained from the intrinsic exciton energies. The experimental results c learly reveal a sample-dependent change of the biaxial strain in the G aN layers with increasing hydrostatic pressure.