Selective uv-laser processing for lift-off of GaN thin films from sapphire substrates

摘要

Gallium nitride (GaN) thin films on sapphire substrates were successfully separated and transferred onto Si substrates by pulsed UV-laser processing. A single 600 mJ/cm~2, 38 ns KrF excimer laser pulse was directed through the transparent substrate to induce a rapid thermal decomposition of the GaN at the GaN/sapphire interface. The decomposition yi8elds metallic Ga and N_2 gas that allows separation of the GaN film from the substrate. Three-micron-thick free-standing GaN membranes were also fabricated using the laser life-off technique. Surface roughness of the exposed interfacial layer was meausred to be approx 24 nm (rms) by atomic force microscopy. Photoluminescence measurements of the GaN membranes showed no optical degradation of the GaN after liftoff from the saphire. Based on a 10 meV blue-shift of the donor-bound exciton peak, an estimated biaxial compressive stress of approx 0.4 GPa in the GaN film was relieved by separation from the sapphire growth substrate.