DONOR-ACCEPTOR PAIR IN MOLECULAR-BEAM EPITAXY-GROWN GAN

We have recently found evidence of new donor acceptor pair (DAP) lumin escence in molecular beam epitaxy (MBE) grown films. A variety of nomi nally undoped samples have been studied by photoluminescence (PL) over a temperature range of 5-300 K. The samples show intensive luminescen ce al energies of 3.404-3.413 eV varying with different sample at 5 K, as well as a fairly strong (DX)-X-0 line at low temperature. We attri bute the Line at 3.404-3.413 eV to DAP recombination which is over 0.1 eV different from the well known DAP caused by ME-doping in GaN. The DAP line shows fine structure. it even predominates in one particular sample. The peak position shifts to higher energy with temperature inc reasing from 5 up to 70 K, and as the excitation laser intensity incre ases. The data are consistent with DAP luminescence involving an accep tor level of about 90 meV (presumably carbon) above the valence band e dge in GaN. It is much shallower than the acceptor level of 250 meV pr oduced by the p-type dopant Mg which is commonly used at present. (C) 1997 Elsevier Science S.A.