Selective photoluminescence of donor-acceptor pairs was used to study compensating donors in p-type layers which had been grown by means of molecular beam epitaxy, and doped with N from a radio-frequency plasma. More than 13 lines were identified in the energy range of optical phonons. It was demonstrated that the dominant features were associated with local modes of N bound phonons. Transitions which involved a shallow donor with a binding energy of 0.0291eV were also revealed. This donor had never previously been reported and, contrary to popular opinion, it was not one of the residual impurities that were usually found in non-intentionally doped layers. Two lines were attributed to resonant donor-acceptor pair photo-neutralization in the n = 2 states of a deep donor. The deep-donor ionization energy was thereby deduced to be 0.0452eV.

C.Morhain, E.Tournié, G.Neu, C.Ongaretto, J.P.Faurie: Physical Review B, 1996, 54[7], 4714-21