Evaluation of GaN by photoluminescence measurement

Comparison of the room-temperature photoluminescence (PL) spectra from a high-quality freestanding GaN template and an average-quality GaN layer on sapphire substrate shows that the width of the exciton band in the former may be twice larger than that in the latter. The surprising fact can be explained by a wide depletion region and large diffusion length of photogenerated carriers in high-quality GaN templates. Photogenerated electrons and holes in this material recombine at larger distance from the surface, and the exciton emission from this depth experiences stronger absorption that causes distortion of the near-bandedge PL and its broadening. We also explain why the intensity of the exciton emission may be low and the defect-related PL may dominate in the room-temperature PL spectrum of high-quality samples. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim