Strain-tunable band alignment and band gap of GaSe/WTe2 heterojunction for water splitting and light-emitting

Abstract

Van der Waals heterojunctions (vdWHs) based on transition metal dichalcogenides (TMDs) attract much attention due to their unique electrochemical and physical properties. However, most vdWHs in TMD family are type II with indirect band gap. For vdWHs in TMD family, it is difficult to obtain the direct band gap through band arrangement approaches, limiting their applications in optoelectronics and photocatalysis. In present work, a type-I GaSe/WTe2 heterojunction with direct band gap (1.13 eV) is found by first-principles calculations. We find that this heterojunction has dipoleallowed direct band gap transition and large band offsets, which are beneficial to light emission efficiency. The effects of strain on electronic structure and optical properties of GaSe/WTe2 heterojunction are investigated. We find that band gap of type-I GaSe/WTe2 heterojunction can be tuned in large range by strain and it is a promising platform to develop strain-tunable light-emitting device which can emit various wavelengths. The band alignment type of GaSe/WTe2 heterojunction can be tuned from type-I to type-II by strain. Our results show that, in type-II alignment, it has efficient photocatalyticactivity in water splitting and the photocatalytic efficiency can be enhanced by strain. We hope our work can make a contribution to exploring a strain-tuned platform for photocatalytic and light-emitting devices.