Experimental and numerical investigation on GaN/Al₂O₃ laser lift-off technique

Transient temperature field of GaN films has been analyzed by finite element method for laser lift-off (LLO) technique. Temperature distribution in GaN films irradiated by pulse laser with different energy density as a function of time and depth has been simulated. The results show that the high temperature region in GaN films localizes within about 70 nm below the GaN/Al₂O₃ interface. It is also found that the energy density of the pulse laser should be confined to a certain range decided by the simulation to realize damage-free GaN films LLO from sapphire substrates. LLO experiments have also been carried out using KrF excimer laser with 248 nm wavelength and 30 ns pulse width. GaN films are separated from sapphire substrates using the parameters obtained from the simulation. Atomic force microscopy, scanning electron microscopy and photoluminescence measurements show that the surface morphology and optical characteristic of GaN films degrade a little after LLO.