Wavelength-Tunable Interlayer Exciton Emission at the Near-Infrared Region in van der Waals Semiconductor Heterostructures.

The wavelength-tunable interlayer exciton (IE) from layered semiconductor materials has not been achieved. van der Waals heterobilayers constructed using single-layer transition metal dichalcogenides can produce continuously changed interlayer band gaps, which is a feasible approach to achieve tunable IEs. In this work, we design a series of van der Waals heterostructures composed of a WSe2 layer with a fixed band gap and another WS2(1-x)Se2x alloy layer with continuously changed band gaps. The existence of IEs and tunable interlayer band gaps in these heterobilayers is verified by steady-state photoluminescence experiments. By tuning the composition of the WS2(1-x)Se2x alloy layers, we realized a very wide tunable band gap range of 1.97-1.40 eV with a wavelength-tunable IE emission range of 1.52-1.40 eV from the heterobilayers. The time-resolved photoluminescence experiments show the IE emission lifetimes over nanoseconds.