Lattice Strain In Bulk Gan Epilayers Grown On Crn/Sapphire Template

Microphotoluminescence spectroscopy is used to investigate local strain in GaN films grown on c-sapphire with CrN buffer, where the CrN buffer is partly etched. Biaxial compressive strain dominates GaN films grown on CrN buffer/c-plane sapphire. The emission energies of (DX)-X-0, FXA, and FXA-1LO emission lines shift gradually from a high value to a low one, as the excitation laser beam scans from the unetched side of the sample to the etched side, while the emission intensities show only a slight change. No cracking occurs in the GaN film during etching except a change in bending of the detached part of the GaN film from convex to concave as determined by surface profiler. Both the lattice parameter and the energy position of the bound exciton emission peaks from a completely detached GaN are almost the same as those reported for strain-free GaN. The line width of the (0002) omega scan of a GaN film is narrowed from 352 to 331 arc sec through detaching presumably due to decrease in bending. Those properties suggest that gradual lattice strain relaxation takes place in GaN layers grown on CrN buffer as etching of CrN buffer proceeds and that the chemical lift-off enables to detach a GaN film from a sapphire substrate without generating defects.