Effect of Annealing on Thermal Expansion Behavior of Free-Standing GaN

During the rapid evolution progress of GaN based optoelectronic devices, GaN bulk material with high crystal quality is regarded as the hope of breakthrough for their efficiency and lifetime. In present work, free-standing GaN films with different thickness were obtained with laser lift-off (LLO) technique after the growth by hydride vapor phase epitaxy (HVPE). The samples were annealed at 1500 K. The temperature dependent lattice parameters of all samples were measured with high resolution X-ray diffractometer (HRXRD). The temperature dependent Raman scattering spectra were measured to analyze the stress in GaN films. The effect of annealing on the changing of thermal expansion coefficient of GaN was studied and the release of bending and residual strain of GaN was characterized.