YELLOW LUMINESCENCE AND RELATED DEEP STATES IN UNDOPED GAN

Photocapacitance spectra in undoped, metal-organic vapor-phase-epitaxy -grown GaN layers, in a range of a photon energies from 0.6 to 3.5 eV, reveal two main persistent features: a broad increase of the capacita nce from 2.0 to 2.5 eV, and a steep decrease at 1 eV, only observed af ter a previous Light exposure to photon energies above 2.5 eV. A deep trap (E(v)+1 eV) that captures photoelectrons from the valence band, a fter being emptied with photons above 2.5 eV, is proposed as the origi n of these features. Optical-current deep-level transient spectroscopy results also show the presence of a trap at 0.94 eV above the valence band, only detected after light excitation with photon energies above 2.5 eV. A correlation is found between the ''yellow band'' luminescen ce intensity at 2.2 eV and the amplitude of the photocapacitance decre ase at 1 eV, pointing to a deep trap at 1 eV above the valence band as the recombination path for the yellow band. The detection of the yell ow band with below-the-gap photoluminescence excitation supports the p roposed model.