Reversible ultraviolet-induced photoluminescence degradation and enhancement in GaN films

Abstract

UV-induced modifications in undoped metalorganic chemical vapor deposition grown GaN on sapphire are observed from 9 to 160 K. The photoluminescence intensities of bound excitons (3.476, 3.482 eV), the yellow band (2.2 eV) and the blue band (2.9 eV) change with time when a fresh sample is irradiated by 325 nm (He–Cd laser). The free exciton peak at 3.488 eV is unchanged by laser irradiation. Initially the blue and donor-bound exciton emission degrade rapidly and the yellow luminescence increases, each at the same rate. Later, the yellow luminescence degrades and the donor-bound exciton emission increases very slowly, at the same rate. Mechanisms are proposed that may explain the luminescence pathways and defects involved.