Broken-Gap Type-III Band Alignment in WTe₂/HfS₂ van der Waals Heterostructure

Van der Waals heterostructures (vdWHs) are attracting a lot of interest for fundamental studies and fabricating novel devices. Currently, most vdWHs exhibit type-I or type-II band alignment, and few systems have been shown to be in the type-III class. Herein, we show first-principles evidence that WTe₂/HfS₂ vdWH possesses the long-sought type-III band alignment with a broken gap, providing a promising platform for developing tunnel field-effect transistors. Moreover, the electronic features of WTe₂/HfS₂ vdWH can be effectively modulated via external strain and electric field. Particularly, an interesting transition from type-III to type-II band alignment can be observed in WTe₂/HfS₂ vdWH upon the application of strain or electric field, which holds great potential for designing multifunctional devices. Our study not only predicts an extraordinary vdWH with type-III band alignment but also provides an outstanding candidate for realizing multiple band alignment transformation.