  Few-layer InSe draws tremendous research interests owing to the superior
electronic and optical properties. It exhibits high carrier mobility up to more
than 1000 cm2/Vs at room temperature. The strongly layer-tunable band gap spans
a large spectral range from near-infrared to the visible. In this perspective,
we systematically review the optical properties of few-layer InSe. Firstly, the
intrinsic optical and electronic properties are introduced. Compared to other
two-dimensional (2D) materials, the light-matter interaction of few-layer InSe
is unusual. The band gap transition is inactive or extremely weak for in-plane
polarized light, and the emission light is mainly polarized along the
out-of-plane direction. Secondly, we will present several schemes to tune the
optical properties of few-layer InSe such as external strain, surface chemical
doping and van der Waals (vdW) interfacing. Thirdly, we survey the applications
of few-layer InSe in photodetection and heterostructures. Overall, few-layer
InSe exhibits great potential not only in fundamental research, but also in
electronic and optoelectronic applications.
