Wafer-scale fabrication of single-crystal graphene on Ge(110) substrate by optimized CH4/H2 ratio

The synthesis of high-quality wafer-scale single-crystal graphene is indispensable for the commercial applications of graphene-based electronic and photonic devices. Previously large-scale single-crystal graphene was successfully acquired by various growth optimization whereas the methods vary from lab to lab due to the complicated process of chemical vapor deposition. Here we present an approach to fabricate monolayer single-crystal graphene on 4-inch Ge(110) wafer by tuning CH4/H-2 ratio precisely. By directly monitoring the growth process of graphene via atomic force microscopy, it is found that under high CH4/H-2 ratio condition new graphene domains ceaselessly nucleate and enlarge during the whole growth process, while under low CH4/H-2 ratio condition, the density of graphene domains is saturated at early stage, which causes the formation of single-crystal graphene. Terahertz time domain spectroscopy shows that the average carrier mobility of single-crystal graphene wafer is as high as 26351 cm(2)/V.s, comparable to that of the exfoliated graphene. This work provides an efficient and reliable approach to fabricate wafer-scale single-crystal graphene for microelectronics and optoelectronics applications in the future.