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 ba nd the deep levels spectra measured by optical transient current spect roscopy (OTCS) is always dominated by a hole trap at E-v + 0.85 eV whi ch is absent in the spectra of the samples with weak yellow luminescen ce. Based on the results of recent theoretical calculations it is sugg ested that these traps could be gallium Vacancies V-Ga and that the ce nters responsible for yellow luminescence are formed by pairing such v acancies with shallow donors. The results indicate that the yellow lum inescence band could be the dominant recombination channel in the samp les with strong yellow luminescence band whereas in the samples with w eak yellow luminescence recombination this role is taken over by nonra diative recombination centers. Deep levels transient spectroscopy (DLT S) measurements revealed the existence of a barrier for capture of ele ctrons for electron traps at E-c-0.55 eV (0.15 eV) and E-c-0.8 eV (abo ut 0.35 eV) and a possible role of such traps in persistent photocondu ctivity at room temperature in n-GaN is discussed. (C) 1998 Elsevier S cience Ltd. All rights reserved.