Phase-Dependent Band Gap Engineering in Alloys of Metal-Semiconductor Transition Metal Dichalcogenides

Bandgap engineering plays a critical role in optimizing the electrical and optical properties of semiconductors. Alloying can be used to tune band gaps by combining isovalent semiconductors. Here, we present a novel form of bandgap engineering involving alloying non-isovalent cations in a two-dimensional transition metal dichalcogenide [1]. By alloying semiconducting MoSe₂ with metallic NbSe₂, two structural phases of Mo_0.5Nb_0.5Se₂, 1T and 2H, are produced, each with emergent electronic structure. At room temperature, the 1T and 2H phases are semiconducting and metallic, respectively. Electron diffraction patterns of the 1T structure show the presence of a nearly commensurate charge density wave (NCCDW). Density-functional theory calculations confirm that local distortions open a band gap in 1T-Mo_0.5Nb_0.5Se₂ by facilitating charge transfer. In 2H-Mo_0.5Nb_0.5Se₂, electrical transport measurements show a low-temperature transition to a commensurate CDW state with a bandgap. Our work expands the boundaries of alloy-based band gap engineering by using alloying to access CDW phases.

[1] S. Wang et al., Advanced Functional Materials (2020). https://doi.org/10.1002/adfm.202004912