Near-threshold gain mechanisms in GaN thin films in the temperature range of 20-700 K

We report the results of an experimental study on near-threshold gain mechanisms in optically pumped GaN epilayers in the temperature range of 20-700 K. High-quality single-crystal GaN films grown on 6H-SiC and (0001) sapphire were used in this study. We show that the dominant near-threshold gain mechanism is inelastic exciton-exciton scattering for temperatures below similar to 150 K, characterized by band-filling phenomena and a low stimulated emission (SE) threshold. An analysis of both the temperature dependence of the SE threshold and the relative shift between stimulated and band-edge-related emission indicates electron-hole plasma is the dominant gain mechanism for temperatures exceeding 150 K. Based on our results, we discuss possibilities of reducing the room-temperature lasing threshold in laser diode structures with a GaN active medium. (C) 1999 American Institute of Physics. [S0003-6951(99)01401-1].