Strain at the surface of GaN epilayers and at GaN/sapphire interface before and after laser lift-off (LLO) from the sapphire substrate

摘要

Four GaN epilayers were grown on sapphire by hydride vapor phase epitaxy. The lattice and thermal expansion coefficient mismatches between the epilayers and the sapphire produce a strain in the structure. The strain at the surface of the epilayers was estimated using photoluminescence. By analyzing the variation of the surface strain with thickness, the minimum thickness required to obtain low surface strain was estimated to be approximately 45 μm. Furthermore, the strain at the interface of the sapphire and the epilayers was estimated after laser lift-off of GaN epilayers. The analysis showed that a low and almost constant strain at the surface of the interface for the separated samples can be obtained for an epilayer thickness greater than 18 μm.