Computational Assessment of I-V Curves and Tunability of 2D Semiconductor van der Waals Heterostructures

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have received significant interest for use in tunnel field-effect transistors (TFETs) due to their ultrathin layers and tunable band gap features. In this study, we used density functional theory (DFT) to investigate the electronic properties of six TMD heterostructures, namely, MoSe₂/HfS₂, MoTe₂/ZrS₂, MoTe₂/HfS₂, WSe₂/HfS₂, WTe₂/ZrS₂, and WTe₂/HfS₂, focusing on variations in band alignments. We demonstrate that WTe₂/ZrS₂ and WTe₂/HfS₂ have the smallest band gaps (close to 0 or broken) from the considered set. Furthermore, combining DFT with the nonequilibrium Green's function method (DFT-NEGF), we analyzed the output I-V characteristics, revealing increased current as band gap closes across all studied heterostructures. Notably, WTe₂/ZrS₂ and WTe₂/HfS₂ show a potential negative differential resistance (NDR) even without a broken gap. Importantly, the inclusion of a p-doped gate effect in WTe₂/ZrS₂ enhances the current flow and band-to-band tunneling. The rapidly increasing tunneling current under low applied voltage indicates that the WTe₂/ZrS₂ and WTe₂/HfS₂ heterostructures are promising for applications in TFETs.