Studies of the origin of the yellow luminescence band, the nature of nonradiative recombination and the origin of persistent photoconductivity in n-GaN films

It is shown that in n-GaN samples with a strong yellow luminescence band the deep levels spectra measured by optical transient current spectroscopy (OTCS) is always dominated by a hole trap at E-v + 0.85 eV which is absent in the spectra of the samples with weak yellow luminescence. Based on the results of recent theoretical calculations it is suggested that these traps could be gallium Vacancies V-Ga and that the centers responsible for yellow luminescence are formed by pairing such vacancies with shallow donors. The results indicate that the yellow luminescence band could be the dominant recombination channel in the samples with strong yellow luminescence band whereas in the samples with weak yellow luminescence recombination this role is taken over by nonradiative recombination centers. Deep levels transient spectroscopy (DLTS) measurements revealed the existence of a barrier for capture of electrons for electron traps at E-c-0.55 eV (0.15 eV) and E-c-0.8 eV (about 0.35 eV) and a possible role of such traps in persistent photoconductivity at room temperature in n-GaN is discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.