Depth dependence of defect density and stress in GaN grown on SiC

We report high resolution x-ray diffraction studies of the relaxation of elastic strain in GaN grown on SiC 0001 . The GaN layers were grown with thickness ranging from 0.29 to 30 m. High level of residual elastic strain was found in thin 0.29 to 0.73 m thick GaN layers. This correlates with low density of threading screw dislocations of 1-2 107 cm−2, observed in a surface layer formed over a defective nucleation layer. Stress was found to be very close to what is expected from thermal expansion mismatch between the GaN and SiC. A model based on generation and diffusion of point defects accounts for these observations.