Structural investigation of InGaN/GaN LEDs prepared by femtosecond laser lift-off

Laser lift-off (LLO) has become a viable technique to detach epitaxially grown light-emitting diodes (LEDs) from their original sapphire substrates. In conventional LLO, intense UV irradiation from e.g. excimer lasers with pulse widths in the nanosecond regime is applied. It is directed to the backside of the wafer, transmitted through the sapphire substrate and then linearly absorbed at the interface to the epitaxially grown GaN stack, resulting in thermal decomposition of the first layers. As an alternative novel approach, we present a successful implementation of LLO process with 350 fs short pulses in the green spectral range (520 nm) based on two-photon absorption mechanism. By means of electroluminescence measurements and electron microscopy (i.e., SEM and TEM), the impact of the irradiation on the GaN crystal quality has been investigated and compared with that from conventional lift-off processes.