Stress analysis of transferable crack-free gallium nitride microrods grown on graphene/SiC substrate

Crack-free GaN microrods were fabricated on graphene/SiC substrate by hydride vapor phase epitaxy. The GaN microrods were hexagonal with the diameter up to 100 µm and the height above 80 µm. Raman spectra showed that E2-high peak frequency of GaN microrod near the graphene/SiC surface had 0.3 cm−1 decrease compared to stress-free GaN, the stress of the GaN microrod was 0.071 GPa. As a result, the microrods were crack-free and can be easily released by micro-mechanical exfoliation technology. After exfoliation, Raman spectra showed that graphene still existed at separated region on the surface of SiC substrate, but only GaN peaks were observed from the bottom surface of GaN microrods. GaN microrods were released from the surface of graphene instead of being released together with graphene.