Interfacial Engineering of Single-Layer Graphene/GaN Heterojunctions: Few-Layer h-BN and GaN Lattice Orientations

Understanding the regulation mechanism of GaN lattice orientation and hexagonal boron nitride (h-BN) layer thickness on the electrical and interfacial physical properties of single-layer graphene (SLG)/GaN heterojunctions is crucial for enhancing photoelectric performance of heterojunction devices. Here, we report the role of h-BN insertion layers (1–5 layers) and GaN lattice orientations (polar Ga-plane and N-plane, semipolar r-plane and nonpolar a-plane) in modulating the electrical and interfacial physical properties of SLG/GaN heterojunctions, including barrier height and charge transfer. The structure and electrical properties of the heterojunction were characterized using Raman spectrometer, scanning electron microscopy, and probe station. Increasing the h-BN thickness can enhance 10 interface-related parameters (e.g., barrier height) while suppressing current and reducing 4 charge transfer-related parameters (e.g., Fermi level shift) in heterojunctions. Initial h-BN insertion significantly boosts threshold voltage while suppressing current. The SLG/GaN heterojunction on r-plane GaN exhibits the highest current response at fixed voltage among all orientations, whereas the a-plane configuration shows the lowest response, with current enhancement ranging from 2.278× (minimum, r-plane) to 7.536× (maximum, N-plane). Heterojunctions on semipolar r-plane and nonpolar a-plane GaN exhibit markedly distinct current responses and physical properties compared to those on polar GaN surfaces (Ga- and N-planes), which show relatively minor variations in interface states, electrical properties, and certain physical properties such as barrier height. Contact potential difference (CPD) variation partially reflects charge transfer efficiency. These insights advance the development of interface engineering strategies for graphene/GaN heterojunctions and facilitate the fabrication of heterojunction-based devices.