The same band alignment of two hybrid 2D/3D vertical heterojunctions formed by combining monolayer MoS2 with semi-polar (11–22) GaN and c-plane (0001) GaN

Abstract

Traditional c-plane (0001) GaN based devices are subject to a strong polarization field at the hetero-interfaces which handicaps the performance of photoelectric devices. However, the semi-polar (11–22) GaN has great potential for reducing the polarization effects compared with c-plane (0001) GaN. Here, we have fabricated MoS2/(11–22) GaN heterojunction and determined the band alignment by X-ray photoelectron spectroscopy (XPS). For comparison, the band alignment of MoS2/(0001) GaN heterojunction has also been measured to explore the influence of GaN with different crystal orientations on the energy band of MoS2/GaN heterojunction. Surprisingly, the band alignments of the two MoS2/GaN heterojunctions are the same, which could be caused by the unsaturated and omnidirectional properties of van der Waals forces at the interface of MoS2 and GaN. The measurement result of the valence band offsets (VBOs) of the two MoS2/GaN heterojunctions is 1.54 ± 0.15 eV. And the conduction band offsets (CBOs) are determined to be 0.29 ± 0.15 eV, revealing type-II band alignments of the two heterojunctions. We have also confirmed the number of MoS2 layers on the MoS2/GaN heterojunctions by Raman spectroscopy and the orientations of the GaN substrates by X-ray diffraction. The determination of band alignments between two-dimensional (2D) MoS2 and three-dimensional (3D) semi-polar (11–22) GaN opens up a way for modeling and designing high performance photoelectric devices based on hybrid MoS2/semi-polar GaN heterojunctions.