OPTICAL-PROPERTIES OF GAN EPILAYERS GROWN ON SI(111) AND SI(001) SUBSTRATES

We report the observation of bright photoluminescence (PL) emission fr om two types of GaN epilayers grown by molecular beam epitaxy (MBE). W urtzite phase GaN/Si (111) epilayers are grown by gas source MBE proce ss, whereas cubic phase GaN epilayers are grown on (001) Si covered by thin SIC film in the process of Si annealing in propane prior to the GaN growth. PL emissions are identified based on the results of detail ed PL and time-resolved PL investigations. For the wurtzite phase GaN we observe an efficient up in the energy transfer from bound to free e xcitons. This process is explained by a large difference in the PL dec ay times for two types (free and bound (donor, acceptor)) of excitonic PL emissions. For cubic phase GaN we confirm recent suggestion that a ccepters have smaller thermal ionization energies than those in the wu rtzite phase GaN. (C) 1997 Elsevier Science S.A.