Origin of microstructural defects in single-crystalline films van der Waals epitaxy on graphene

Van der Waals epitaxy (vdWE) of three-dimensional (3D) semiconductors on 2D materials has broad prospects for integrating their distinguishing features. However, many defects, including grain boundaries, basal plane stacking faults (BSFs), and threading dislocations (TDs), exist in the 3D semiconductors, and the origin of those defects has not been studied systemically. Here, we investigate the origin of microstructural defects systemically in a case of single-crystalline GaN films vdWE on graphene. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used for macroscopic and microscopic characterization of the defects of GaN films. Low-angle grain boundaries were existed in the initial 1-2 pm, and the BSFs were formed at the interface of GaN about 200 nm. Moreover, the mixed TDs, as one of threading TDs, were the main line defects in GaN films. This research provides a systematic introduction of various defects (volume, plane, and line defects) in 3D semiconductors vdWE on 2D materials.