INFLUENCE OF RAPID THERMAL ANNEALING ON THE OPTICAL-PROPERTIES OF GALLIUM NITRIDE GROWN BY GAS-SOURCE MOLECULAR-BEAM EPITAXY

Raman scattering, photoluminescence (PL), and nuclear reaction analysi s (MA) have been employed to investigate the effects of rapid thermal annealing (RTA) on GaN films grown on sapphire (0001) substrates by ga s-source molecular-beam epitaxy, The Raman spectra showed the presence of the E-2 (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 signific ant effect on the strain relaxation caused by the lattice and thermal expansion misfit between the GaN epilayer and the substrate. The PL pe ak 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 an nealing time. This effect was attributed to H concentration variation in the GaN film, which was measured by NRA. A high H concentration exi sts in as-grown GaN, which can neutralize the deep level, and the H-bo nded complex dissociates during RTA, This leads to the appearance of a luminescent peak in the PL spectrum. (C) 1998 American Institute of P hysics.