Tunable-Bandgap Transition Metal Dichalcogenides Enabled by Strain Engineering

Strain engineering offers a tool for tuning of the electronic and optoelectronic properties of two-dimensional (2D) materials. In this study, we demonstrate a direct strain engineering method to tune the bandgaps of transition metal dichalcogenides using selenium substitution to synthesize highly strained MoSe₂ film. We observe that during the annealing step, the synthesized MoSe₂ demonstrates a high and homogeneous in-plane tensile strain (4.9%), due to the lattice mismatch with the template materials, higher than method of bending substrates (~2%) or wrinkling. The strain is therefore tuned by adjusting the substitution temperature, which modulate the MoSe₂ bandgap upto ~0.47 eV, concurrently with an enhanced Hall mobility to 797 cm²/Vs, comparable with the high record (~240 cm²/Vs) from WS₂ samples. Consequently, the responsivity of the device is significantly improved from 0.15 to 0.77 mA/W for high-strain MoSe₂ photodetector under near-infrared (1060 nm) illumination. This controllable chalcogen substitution method provides a new strategy for fabricating 2D van der Waals materials with controllable and uniform strain, which has great significance for enhancing the performance of optoelectronic devices.