Reversible direct-indirect band transition in alloying TMDs heterostructures via band engineering

Abstract

Alloying is a feasible and practical strategy to tune the electronic properties of 2D layered semiconductors. Here, based on first-principles calculations and analysis, we demonstrate band engineering through alloying W into a prototype MoS2/MoSe2 heterostructure. Especially, when the W compositions x > 0.57 in Mo1-xWxS2/MoSe2, it exhibits remarkable and reversible direct- to indirect-gap transition. This is because for Mo1-xWxS2/MoSe2, the valence band maximum located at the K point originates from dominant MoSe2, while the competing Gamma state stems from the hybridization of both Mo1-xWxS2 and MoSe2, which is extremely sensitive to the interlayer coupling. Consequently, alloying in MoS2 layer induces direct- to indirect-gap transition and gap increase due to the weakened p-d coupling. We also observe that whether initial alloying in MoS2 or MoSe2, the mu Mo-mu W poor condition should always be used. Our findings are generally applicable and will significantly expand the band engineering to other alloying TMDs heterostructures.