Abstract
Picosecond time-resolved photoluminescence (PL) spectroscopy has been used to investigate the optical properties of an insulating GaN epilayer grown by metalorganic chemical vapor deposition on a sapphire substrate. Two emission lines at 3.503 and 3.512 eV in the continuous wave (cw) PL spectra observed at 10 K under a low excitation intensity (∼23 W/cm2) were identified as the band-to-band transitions involving the A and B valence bands, respectively. A third emission line at 3.491 eV was identified as a band-to-impurity transition involving a shallow donor. The PL decay behavior can be well understood with a model taking into account both the free carriers and impurities. The effective recombination lifetime of the band-to-band transition in GaN was found to be about 3.7 ns. Possible mechanisms for the band-to-band transition being dominant in this high quality insulating GaN epilayer have also been discussed.
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