Reversible Band Alignment Transition in WS2/InSe Heterostructures Enabled by Strain Engineering

Abstract

Assembling 2D van der Waals heterostructures by stacking different 2D layered semiconductors is attracting tremendous interest owing to its advancements in electronics and optoelectronics. A key factor determining the application scenarios of these heterostructures is the band alignment, particularly the significance of type-I alignment (straddling gap) in photo-emitting diodes and type-II alignment (staggered gap) in photodetectors. Switching the band alignment without altering the constituent materials enables convenience and operability for multi-functionalization in single heterostructure. However, it remains challenging to identify a convenient technology for band structure engineering to achieve the desired band alignment transition. Here, through a designed thickness selection, a reversible band alignment transition is demonstrated in the 1L-WS₂/nL-InSe heterostructures (n = 9, 10, 11) by applying tensile strain. This transition can be attributed to the switch in the relative positions of the valence band maximums induced by effective modulation of the band structures. This work presents a convenient strategy for designing band structures of 2D heterostructures, achieving a reversible band alignment transition within a single heterostructure. This offers significant guides for the design of optoelectronic devices with specific functionalities.