Influence of nitridation on III-nitride films grown on graphene/quartz substrates by plasma-assisted molecular beam epitaxy

Growing III-nitride semiconductors on non-single-crystalline substrates at low temperature is essential to realize low-cost and large-area GaN-based transferable and flexible devices. Two-dimensional (2D) layered materials such as graphene have the similar in-plane lattice arrangements compare with III-nitrides, hence III-nitrides can be grown on various non-single-crystal substrates through van der Waals epitaxy (vdWE) assisted by 2D layered material. Nevertheless, because of the low chemical reactivity of perfect graphene surface, it is hard to obtain high-quality GaN thin film with smooth surface without any artificial treatments at the initial stage of epitaxy growth. In this work, the influence of nitridation process on vdWE grown III-nitride films on graphene/quartz substrates has been investigated by using plasma-assisted molecular beam epitaxy. It is demonstrated that moderate intentional defects can be introduced into the surface of graphene/quartz substrate by N-2 plasma treatments in the initial stages of vdWE, which is beneficial to the following nucleation process of III-nitrides. Besides, suitable nitridation conditions are essential in order to obtain high-quality GaN film on graphene/quartz substrates at low growth temperature. Such results can act as paradigms for vdWE of III-nitrides when using other 2D layered materials or non-single-crystalline substrates.