Giant light emission enhancement in strain-engineered InSe/MS$_2$ (M=Mo,W) van der Waals heterostructures

TL;DR

This paper demonstrates that layer-selective strain engineering in InSe/MS2 heterostructures significantly enhances photoluminescence by enabling strain-activated charge transfer, offering new opportunities for optoelectronic device design.

Contribution

It introduces strain engineering as a novel method to tailor band alignment and optical properties in van der Waals heterostructures, supported by experimental and first-principles evidence.

Findings

Giant photoluminescence enhancement in InSe via strain

Strain-activated direct charge transfer from MS2 to InSe

Potential for improved optoelectronic applications

Abstract

Two-dimensional crystals stack together through weak van der Waals (vdW) forces, offering unlimited possibilities to play with layer number, order and twist angle in vdW heterostructures (HSs). The realisation of high-performance optoelectronic devices, however, requires the achievement of specific band alignments, $k$-space matching between conduction band minima and valence band maxima, as well as efficient charge transfer between the constituent layers. Fine tuning mechanisms to design ideal HSs are lacking. Here, we show that layer-selective strain engineering can be exploited as an extra degree of freedom in vdW HSs to tailor their band alignment and optical properties. To that end, strain is selectively applied to MS$_2$ (M=Mo,W) monolayers in InSe/MS$_2$ HSs. This triggers a giant PL enhancement of the highly tuneable but weakly emitting InSe by one to three orders of magnitude. Resonant PL excitation measurements, supported by first-principle calculations, provide evidence of a strain-activated direct charge transfer from the MS$_2$ MLs toward InSe. This significant emission enhancement achieved for InSe widens its range of applications for optoelectronics.