Impact of ultraviolet-laser heating on the photoluminescence of ensembles of GaN microcrystallites

We present optical analysis concerning the redshift of the photoluminescence (PL) of ensembles of GaN microcrystals. We found that the extent of the redshift depends on the laser power as well as on the size of the ensemble. For ensembles of similar to30 mum, the laser power in our experimental specification impacted the PL energy and caused a redshift of up to 120 meV. This phenomenon was not observed for a small ensemble of similar to1 mum or less. For the small ensemble, the PL redshift was negligible and depended weakly on the laser power; similar behavior was found in GaN thin film. The above findings were observed in the PL of GaN microcrystalline of wurtzite as well as the cubic structure. Our results point to a laser heating event occurring in the large ensemble; the emitted scattered light is confined among the microcrystallites thus causing heating. For a small ensemble, the light has a higher probability of diffusing outside the enclosure, and thus no laser heating occurs. (C) 2003 American Institute of Physics.