Optical characterizations of GaN/MoS2 van der Waals heterojunctions with different band alignments

The integration of gallium nitride (GaN) with 2D molybdenum disulfide (MoS2) to form GaN/MoS2 semiconductor heterojunctions will have high potential applications in novel electronics and optoelectronics. In this study, GaN thin films were grown on pulse-laser-deposited MoS2 layer by plasma-assisted MBE at different substrate temperatures (500 °C, 600 °C and 700 °C, respectively). The energy-band alignments of GaN/MoS2 semiconductor heterostructures were analyzed by X-ray photoelectron spectroscopy. The epitaxial growth conditions of GaN films influenced the band alignment of GaN/MoS2 heterojunction. Type-I heterostructure, a straddling relation between narrow-bandgap MoS2 and wide-bandgap GaN, was observed at the optimized growth temperature of 600 °C. At the same time, photoluminescence (PL) and photoreflectance spectroscopies were employed to analyze the optical properties of MoS2 and GaN/MoS2 heterostructures. The PL and exciton energy transition of 2D MoS2 layer can be enhanced by the capping layer GaN, especially for type-I band alignment structure.