Photoluminescence and Raman scattering in Mg and P co-implanted GaN epitaxial layers

Optical properties of P-Mg co-implanted GaN epitaxial layers with P/Mg concentration ratios of 0-0.5 have been studied. It is found that the photoluminescence intensity significantly increases with the P/Mg ratio, probably due to the suppression of N vacancy generation by co-implanted P atoms. New photoluminescence lines caused by P-related transitions are observed for samples with a large P/Mg ratio. Unlike the usual donor-acceptor pair emission peaks, these newly observed peaks exhibit clear red shifts when the temperature is increased. The P-related emission is found to be associated with the recombination of electrons on the shallow native donors with holes on isoelectronic P traps. The photoluminescence study suggests that the isoelectronic P trap forms a stable charged state in the P-Mg co-implanted GaN with a hole binding energy of approximately 220 meV. In addition, Raman measurements indicate that the P-Mg co-implanted GaN layers are to be annealed at 1200 °C for 10s to achieve a sufficient recovery of crystal quality.