We have grown Mg-doped GaN films by metalorganic chemical vapor deposition with various CP2Mg flow rates. After 750 degrees C postgrowth annealing, p-type GaN films with carrier concentrations and mobilities about 2 X 10(17)/cm(3) and 10 cm(2)/V s, respectively, have been achieved. A dominant photoluminescence (PL) line around 2.9 eV was observed at room temperature. By studying the dependence of PL on excitation density at 20 K, the emission line around 2.95 eV can be attributed to a donor-to-acceptor pair transition rather than to a conduction band-to-impurity transition involving the Mg-related deep level. We suggest that the DAP transition line is caused by a Mg related deep level at about 510 meV above the valence band. It is much deeper than the acceptor level at 250 meV commonly produced by the Mg dopants. (C) 1998 American Institute of Physics. [S0021-8979(98)02720-0]
