High-resolution PL spectra of donor- and acceptor-bound excitons in homoepitaxial GaN-layers

Homoepitaxial GaN layers grown by MOVPE on a pre-treated GaN single crystal are almost strain-free, have very low defect densities and low impurity le vels. These layers show strong, extraordinarily sharp photoluminescence spe ctra. Especially, the donor-(D-0, X) and acceptor-(A(0), X) bound excitons at approximate to 3.471 eV and 3.465 eV, respectively, exhibit line widths of approximate to 100 mu eV, and ample fine structures can be resolved. For the (DO, X), complicated spectra are observed in the spectral region of tw o-electron-transitions and in the excited bound exciton state. For both (DO , X) and (AO, X), the respective bound exciton states belonging to all thre e valence bands are found. By variation of the sample temperature and excit ation density, we separate the spectral features contributed by different i mpurities and reassign several lines in the band gap region. (C) 1999 Elsev ier Science B.V. All rights reserved.