Influence of rapid thermal annealing on the optical properties of gallium nitride grown by gas-source molecular-beam epitaxy

Abstract

Raman scattering, photoluminescence (PL), and nuclear reaction analysis (NRA) have been employed to investigate the effects of rapid thermal annealing (RTA) on GaN films grown on sapphire (0001) substrates by gas-source molecular-beam epitaxy. The Raman spectra showed the presence of the E2 (high) mode of GaN and shift of this mode from 572 to 568 cm−1 caused by annealing. The results showed that RTA has a significant effect on the strain relaxation caused by the lattice and thermal expansion misfit between the GaN epilayer and the substrate. The PL peak exhibited a blueshift in its energy position and a decrease in the full width at half maximum after annealing, indicating an improvement in the optical quality of the film. Furthermore, a green luminescence appeared after annealing and increased in intensity with increasing annealing time. This effect was attributed to H concentration variation in the GaN film, which was measured by NRA. A high H concentration exists in as-grown GaN, which can neutralize the deep level, and the H-bonded complex dissociates during RTA. This leads to the appearance of a luminescent peak in the PL spectrum.