GaN-based films grown on sp³-bonded single-crystalline substrates can maintain the coherent growth character. However, exfoliating III-nitride films from these substrates proves difficult because of the strong sp³-type covalent bonds between the substrates and epilayers. The sp²-bonded two-dimensional (2D) materials exhibit hexagonal in-plane lattice arrangements and weakly bonded layers, so the GaN epilayer grown on 2D materials can be transferred onto foreign substrates with ease. In this paper, graphene is used as the inserted layer (IL) on freestanding GaN substrate and the van der Waals coherent epitaxy of GaN-based single-crystalline films on such graphene/GaN templates is investigated. Density functional theory computations are performed to probe the transmission of crystallographic information of wurtzite GaN through the graphene IL. The appropriate layer numbers of graphene IL and GaN growth temperature are optimized to demonstrate the coherent epitaxy character. Both theoretical and experimental results support that the coherent epitaxy of GaN can only be achieved by using a monolayer graphene IL, and the crystalline quality of optimized GaN film can reach the same level of that grown directly on GaN freestanding substrates.

中文翻译：

---

GaN 和 InGaN/GaN 多量子阱通过石墨烯插入层的范德华相干外延

在sp ³键合单晶衬底上生长的GaN基薄膜可以保持相干生长特性。然而，由于衬底和外延层之间的强 sp ³型共价键，从这些衬底剥离 III 族氮化物膜证明是困难的。SP ²键合二维 (2D) 材料具有六边形面内晶格排列和弱键合层，因此在二维材料上生长的 GaN 外延层可以轻松转移到异质衬底上。在本文中，石墨烯被用作独立式 GaN 衬底上的插入层 (IL)，并研究了这种石墨烯 / GaN 模板上 GaN 基单晶薄膜的范德华相干外延。执行密度泛函理论计算以探测纤锌矿 GaN 的晶体信息通过石墨烯 IL 的传输。石墨烯 IL 的适当层数和 GaN 生长温度经过优化，以证明相干外延特性。理论和实验结果都支持GaN的相干外延只能通过使用单层石墨烯IL来实现，