Stress relaxation of GaN microstructures on a graphene-buffered Al2O3 substrate

GaN microstructures were grown on c-Al2O3 with a multi-stacked graphene buffered layer using metal metal-organic chemical-vapor deposition. Under the same growth conditions, the nucleation of GaN was suppressed by the low surface energy of graphene, resulting in a much lower density of microstructures relative to those grown on c-Al2O3. Residual stress in the GaN microstructures was estimated from the peak shift of the E-2 phonon using micro-Raman spectroscopy. The results showed that the compressive stress of approximately 0.36 GPa in GaN on c-Al2O3 caused by lattice mismatch and the difference in the thermal expansion coefficient was relaxed by introducing the graphene layer. ((c) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)