Optical properties of a high-quality insulating GaN epilayer

Picosecond time-resolved photoluminescence (PL) spectroscopy has been used to investigate the optical properties of an insulating GaN epilayer grown b y metalorganic chemical vapor deposition on a sapphire substrate. Two emiss ion lines at 3.503 and 3.512 eV in the continuous wave (cw) PL spectra obse rved at 10 K under a low excitation intensity (similar to 23 W/cm(2)) were identified as the band-to-band transitions involving the A and B valence ba nds, respectively. A third emission line at 3.491 eV was identified as a ba nd-to-impurity transition involving a shallow donor. The PL decay behavior can be well understood with a model taking into account both the free carri ers and impurities. The effective recombination lifetime of the band-to-ban d transition in GaN was found to be about 3.7 ns. Possible mechanisms for t he band-to-band transition being dominant in this high quality insulating G aN epilayer have also been discussed. (C) 1999 American Institute of Physic s. [S0003-6951(99)04025-5].