Comparative simulation study of intra-layer band-to-band tunneling in monolayer transition metal dichalcogenides

Intra-layer band-to-band tunneling transmission function T(E) through monolayer transition metal dichalcogenides is calculated using the nonequilibrium Green function method combined with the tight-binding approximation. We focus on the differences in T(E) according to structures (nanosheet and nanoribbon) or materials (MoS₂, WS₂, MoSe₂, WSe₂, MoTe₂, and WTe₂). We find T(E) of the nanoribbon structure becomes much lower than that of the nanosheet structure due to the indirect transition and the small spatial overlap of the wave functions at the conduction band (CB) and valence band (VB) edges. In the nanosheet structure, the material dependence of T(E) is shown to be understood in terms of the tunneling mass and the bandgap energy. In the nanoribbon structure, MoTe₂ and WTe₂ show large T(E) due to the large spatial overlap of the wave functions at the CB bottom and VB top. (author)