Contact properties of 2D/3D GaSe/Si(1 1 1) heterostructure

For utilization of two-dimensional (2D) materials in nanoelectronic devices, it is necessary to investigate mixed-dimensional van der Waals (vdW) heterostructures combining those diverse 2D materials with conventional three-dimensional (3D) ones. In this study, we have investigated atomic and electronic structures of heterostructures that consist of 2D GaSe and 3D Si using density functional theory calculations. Especially, we focus on different contact behaviors at heterojunctions between GaSe and Si depending on two types of Si(1 1 1) surface terminations. Calculations show that GaSe/clean Si(1 1 1) (c-Si(1 1 1)) and GaSe/H-covered Si(1 1 1) (H-Si(1 1 1)) heterostructures show semiconductor/metal and semiconductor/semiconductor contact behaviors, respectively. GaSe forms n-type contact with c-Si(1 1 1) and thus Fermi level pinning occurs at GaSe/c-Si(1 1 1) interfaces with metal-induced gap states. In the case of GaSe/H-Si(1 1 1), we identify that the interfaces form p-n heterojunction, especially with type II band alignment. From the understanding of contact behaviors between GaSe and Si(1 1 1), we suggest the possibility of applications in nano- and optoelectronic devices.