Raman spectroscopy study on free-standing GaN separated from sapphire substrates by 532 nm Nd:YAG laser lift-off

Gallium nitride (GaN) thin films grown on sapphire substrates were successfully lifted onto silicon wafers using a laser lift-off (LLO) process induced by a 532 nm, Nd:YAG pulsed laser. Although the photon energy (2.33 eV) is much lower than the band gap of hexagonal GaN (3.41 eV), free-carriers absorption can heat up and consequently causes detachment of the GaN film from the sapphire substrate. Raman measurement conducted before and after LLO showed that the surface structure of the lifted GaN changed from hexagonal to a cubic structure.