Microstructural and optical properties of stress-free GaN films on graphene prepared by PECVD

The van der Waals epitaxy (vdWE) of three-dimensional (3D) semiconductors on 2D materials has broad prospects for integrating the unique advantages of both. In this study, multilayer graphene (MLG) was synthesized by plasma enhanced chemical vapor deposition (PECVD) on sapphire and then flat GaN thin films were obtained through metal organic chemical vapor deposition (MOCVD) assisted by the sputtering of an AlN buffer layer. Transmission electron microscopy (TEM) showed the existence of low-angle grain boundaries and mainly mixed dislocations at the interface of the epitaxial GaN. As the thickness of the GaN film increased, the number of low-angle grain boundaries dropped by an order of magnitude over the initial 1-3 mu m. Spectral lines typical of a stress-free GaN film were seen in the low-temperature photoluminescence (PL) measurements, and the TEM analysis corresponded well with the luminescent peaks. These detailed characterizations offer an avenue for a better understanding of the growth behavior of GaN films grown on graphene and furthermore, for obtaining high-quality GaN.