Residual strain dependence of stimulated emission in GaN layers grown on (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 trimethylgallium. The lattice constants a and c in the layer were estimated by X-ray diffraction. The threshold power density for stimulated emission was measured by photopumping the layers. It was found that the grown layers were elastically deformed and that the residual strain can be sustained by decreasing the Bow rate of trimethylgallium. It was also found that the threshold power density of stimulated emission decreases as the lattice constant a decreases. This tendency indicates that the strain relaxation mechanism is associated with enhancement of nonradiative recombination.