Tuning the Band Alignment and Electronic Properties of GaSe/Sn X 2 ( X = S , Se ) Two-Dimensional van der Waals Heterojunctions via an Electric Field

Abstract

Two-dimensional (2D) material-based van der Waals heterostructures (vdWHs) have been identified as an excellent platform from which to expand various device applications for light-emitting, photovoltaic, and field-effect transistors because of their different band alignments, including type-I, type-II, and type-III. However, it is difficult to achieve transformations between types of band alignment in a single heterostructure for diverse applications. In this study, the effects of a vertical electric field on the band alignment transition and electronic properties of 2D ${\rm{GaSe}}/{\rm{SnS}}_{2}$ (${\rm{SnSe}}_{2}$) vdWHs are investigated systematically using density functional theory calculations. The study shows that the electric field can modulate not only the band gap but also the band alignment to produce multifunctional device applications. A positive electric field can control the band alignment transformation from type-II to type-I for electric field values of approximately 0.39 V/\AA{} (0.12 V/\AA{}), while a negative electric field can transform the type-II to type-III band alignments for electric field values of about \ensuremath{-}0.2 V/\AA{} (\ensuremath{-}0.16 V/\AA{}) in ${\rm{GaSe}}/{\rm{SnS}}_{2}$ (${\rm{SnSe}}_{2}$) vdWHs. We trace these surprising results to the conduction band and valence band edge position movements for the linear decrease of ${\rm{GaSe}}$, while the linear increase of ${\rm{SnS}}_{2}$ (${\rm{SnSe}}_{2}$) occurs with the applied electric field. The present work may provide a direction for tunable multiple-band alignments in 2D vdWHs and help achieve multifunctional device applications.