Argon plasma etching of gallium nitride: spectroscopic surprises

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