RESIDUAL STRAIN DEPENDENCE OF STIMULATED-EMISSION IN GAN LAYERS GROWNON (0001) SAPPHIRE SUBSTRATES

We have grown 1.5 mu m-thick GaN layers on (0001) sapphire substrates by metalorganic chemical vapor deposition with various Bow rates of tr imethylgallium. The lattice constants a and c in the layer were estima ted by X-ray diffraction. The threshold power density for stimulated e mission was measured by photopumping the layers. It was found that the grown layers were elastically deformed and that the residual strain c an be sustained by decreasing the Bow rate of trimethylgallium. It was also found that the threshold power density of stimulated emission de creases as the lattice constant a decreases. This tendency indicates t hat the strain relaxation mechanism is associated with enhancement of nonradiative recombination.