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

Abstract

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