Photoluminescence and Raman spectroscopy of Mg-doped GaN; as grown, hydrogen implanted and annealed

Hydrogen-ion implantation was studied for Mg-doped hexagonal GaN grown on sapphire. Low temperature photoluminescence spectroscopy (PL) shows two significant features; the implantation-annealing induced yellow band (YL) and a remarkable sharp excitonic peak. In the region 1.73–1.79 eV well resolved optical transitions were observed, which resemble the well known R1 and R2 emission bands from Cr3+ in Al2O3 (ruby). Structural and electronic changes were monitored by inelastic light scattering (ILS) spectroscopy. At high implantation dose and high annealing temperature we observed well resolved bands at 320, 380 and 640 cm−1. The latter band ‘splits’ into 645 and 672 bands at the highest implantation dose. Additionally, implantation-annealing induced band was observed at 430 cm−1. This band was not observed before. Besides these, four of the six Raman allowed modes are present in the spectra: 2A1, E1 and E2. Second order Raman spectroscopy yields several bands in the region 860–1470 cm−1. On the high energy side of the spectra, we monitor luminescence bands at 1.878, 1.85, 1.836 eV and for the first time observed a 1.8 eV band. Using a group-theoretical approach we assign symmetries of the first order phonons at k=0 as well as some experimentally observed second order symmetry allowed modes.