Towards controllable optical response of GaN quantum dots in alumina

GaN nanocrystals (in the wurtzite phase) have been synthesized by thermal annealing in reducing atmosphere of Ga++N+ sequentially implanted alumina. We show that the reduction of Ga local concentration (by lowering the implantation dose) yields to an overall increase in the intensity of the GaN photoluminescence signal, to a decrease of the PL bandwidth and to the shift of its onset towards higher energies, due to quantum confinement effects in GaN nanocrystals with a narrow size distribution. The interpretation of the optical results is supported by structural analyses. Moreover, by investigating different forming treatments for GaN synthesis, the key role of hydrogen in the annealing atmosphere is evidenced.