High-temperature stimulated emission studies of MOCVD-grown GaN films

Edge and surface-emitted stimulated emission (SE) in optically pumped GaN thin films was studied in the temperature range of 20 K to 700 K. The single-crystal GaN films used in this work were grown by MOCVD on (0001) sapphire and 6H-SiC substrates.. We have observed that the SE peak shifts from 360 nn at 20 K to 412 mn at 700 K, which is the highest temperature at which SE has been reported for this material. The temperature sensitivity of the SE threshold was studied over the entire temperature range. The characteristic temperature was found to be about 170 K over the temperature range of 300 K to 700 K for samples grown on both sapphire and SiC substrates. The energy position of the SE and spontaneous emission peaks were shown to shift linearly to longer wavelengths with increasing temperature and empirical expressions for this shift are given, We demonstrate that the energy separation between the spontaneous and SE peaks gradually increases from 90 meV at 300 K to 200 meV at 700 K indicating that an electron-hole plasma is responsible for the SE mechanism above room temperature (RT). We demonstrate that the surface-emitted SE in GaN epilayers comes from cracks, burn spots, and other imperfections, and is due to the scattering of a photon flux propagating parallel to the surface. Our results suggest that these defects are effective scattering centers and, under strong optical excitation, become points of origin for burning of the sample surface. This study shows that GaN has an extremely low temperature sensitivity compared to other semiconductors and is suitable for the development of light emitting devices that can operate significantly above RT.