Low‐Energy UV Ultrafast Laser Controlled Lift‐Off for High‐Quality Flexible GaN‐Based Device

Abstract A one‐step laser lift‐off (LLO) for patterned gallium nitride (GaN) film and GaN‐based light‐emitting diode (LED) device is achieved using 355 nm picosecond laser irradiation in this research. The laser fluence required for separation is 0.09–0.13 J cm⁻², which is much lower than that for the currently reported LLO methods. The separated GaN film is intact with only 0.04 GPa of residual stress. The ultra‐smooth separated surface with root mean square roughness of only 5.2 nm is attributed to the interconnection of microcrack‐free flat cavities formed by the combination of high photon energy‐induced intrinsic absorption and subsequent plasma generation. The flat cavity with a depth‐to‐width ratio of 1:4000 limits the delamination region to a few nanometers at the GaN/sapphire interface. GaN‐based LED is transferred with perfect electroluminescence (EL) by the strategy. The stable EL spectral peak positions and intensity independent of the bending state prove that the presented low‐energy ultrafast LLO technique ensured the flexibility of the separated LED device without affecting the performance. This research provides a promising strategy to achieve the LLO of GaN devices with low energy consumption, high controllability, and high efficiency, which is significant for the industrial fabrication of flexible GaN‐based electronics.