Metastability of the UV luminescence in Mg-doped GaN layers grown by MOVPE on quasi-bulk GaN templates

Optical metastability in Mg-doped GaN layers grown by metal–organic vapor phase epitaxy on thick GaN templates grown by halide vapor phase epitaxy has been studied by photoluminescence (PL) and cathodoluminescence (CL). The total Mg concentration varies from 1×1019 to 1×1020 cm−3. Both PL and CL spectra change the initial shape within a few minutes exposure to the excitation source. The effect is permanent at low temperatures but the emission spectrum can be recovered to its initial shape after heating to room temperature. The difference in PL and CL spectra is explained by activation of different regions in the sample by laser and electrons, respectively. In CL the increase of the defect-related luminescence seems to be connected with an enhanced structural defect reaction under electron irradiation, which competes with the regular radiative recombination, while in PL the main effect is related to dissociation of Mg–H complexes with consequent passivation of the residual shallow acceptors.