  Van der Waals heterostructures formed by stacking different types of 2D
materials are attracting increasing attention due to new emergent physical
properties such as interlayer excitons. Recently synthesized atomically thin
indium selenide (InSe) and antimony (Sb) individually exhibit interesting
electronic properties such as high electron mobility in the former and high
hole mobility in the latter. In this work, we present a first-principles
investigation on the stability and electronic properties of ultrathin bilayer
heterostructures composed of InSe and Sb single layers. The calculated
electronic band structures reveal a direct band gap semiconducting nature of
the InSe/Sb heterostructures independent of stacking pattern. Taking spin-orbit
coupling into account, we find a large Rashba spin splitting at the bottom of
conduction band, which originates from the atomic spin-orbit coupling with the
symmetry breaking in the heterostructure. The strength of the Rashba spin
splitting can be tuned by applying in-plane biaxial strain or an out-of-plane
external electric field. The presence of large Rashba spin splitting together
with a suitable band gap in InSe/Sb bilayer heterostructures make them
promising candidates for spin field-effect transistor and optoelectronic device
applications.
