It is shown that bulk MOVPE-grown GaN can exhibit dramatically increased near-band-edge and below-bandgap emission after argon plasma etching. The temperature dependence of the near-band-edge emission shows that donor-bound excitons are the dominant species in Ar-etched samples while free excitons dominate spectra from unetched samples. Under UV illumination and a low temperatures metastable behaviour is apparent from the defect-related blue and yellow luminescence bands. The clear linkage between the yellow and blue emission bands indicates that any microscopic model of the defect(s) associated with the yellow luminescence must also be able to explain the blue luminescence. At room temperature, UV illumination over a period of time enhances the yellow emission by a factor of 20 and it is shown that this effect can be employed for room-temperature optical data storage and retrieval.
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