MAGNESIUM ACCEPTOR LEVELS IN GAN STUDIED BY PHOTOLUMINESCENCE

Magnesium doped GaN epitaxial layers were grown by metal-organic chemi cal vapor deposition on sapphire substrate. Energy levels of these acc epters were investigated by systematic photoluminescence measurements in the temperature range of 12-300 K. Magnesium concentration was vari ed from <1 x 10(19) to higher than 5 x 10(19) cm(-3). Photoluminescenc e measurements were made on the as-grown and annealed samples. We have observed various transitions related to donor to acceptor and their p honon replicas, conduction band to accepters, and free excitons. Their dependence on temperature, concentration of the magnesium impurity an d annealing conditions was discussed. In our study, two important obse rvations were made. First, very deep level luminescence was not observ ed even in the highly magnesium doped as-grown samples. Second, free e xciton transitions including valence band splittings were observed for the first time in the Mg-doped materials, demonstrating the high qual ity of the samples. (C) 1998 American Institute of Physics.