Impact of Interface and Surface Oxide Defects on WS₂ Electronic Properties from First Principles

The industrial-scale growth of dielectrics on top of a 2D material transistor channel without deterioration of its transport characteristics remains challenging today. Here, we investigate the origin of the performance degradation issue by constructing several atomistic interface models between a WS₂ monolayer and an amorphous Al₂O₃ or HfO₂ thin film. We then computed their properties using first-principles methods. We show that, while it is in principle possible to achieve a van der Waals interface between these materials, surface defects (e.g., undercoordinated metal atoms at the surface) are detrimental since they create localized states close to the bottom of the conduction band of WS₂. Even in their absence, the inhomogeneity of the surface topology creates a nonuniform potential that is felt by charge carriers in WS₂. While surface defects can potentially be kept under control with an appropriate oxide choice, the surface inhomogeneity appears to act as a bottleneck, limiting the performance of WS₂ as a transistor channel and, in general, for all 2D materials.