Impact of strain on the excitonic linewidth in transition metal dichalcogenides

Abstract

Monolayer transition metal dichalcogenides (TMDs) are known to be highly sensitive to externally applied tensile or compressive strain. In particular, strain can be exploited as a tool to control the optical response of TMDs. However, the role of excitonic effects under strain has not been fully understood yet. Utilizing the strain-induced modification of electron and phonon dispersion obtained by first principle calculations, we present in this work microscopic insights into the strain-dependent optical response of various TMD materials. In particular, we explain recent experiments on the change of excitonic linewidths in strained TMDs and predict their behavior for tensile and compressive strain at low temperatures.

Disentangling the effects of doping, strain and disorder in monolayer WS2 by optical spectroscopy

“…That is, the larger n-doping density in the dark regions broadens PL emission and the increasing tensile strain in the bright regions narrows the PL linewidth. 51,52 From these measurements we can therefore make the following conclusions regarding the perturbations of this flake: along the lines from the centre to the apexes, there is an elevated (and varying) n-doping density. Away from these lines the doping density gradually decreases and tensile strain begins to take over as the dominant factor affecting the optical properties.…”

Tuning the physical properties of ultrathin transition-metal dichalcogenides via strain engineering

“…Different from the almost unaffected electronic properties of graphene under strain, the electronic properties of ultrathin TMDs are signicantly sensitive to almost all types of mechanical strain, namely shear strain, tensile strain and compressive strain, the strain-induced electronic structural evolution will undoubtedly result in the modication of optical and electrical transport properties. [63][64][65][66] For instance, the existence of continuously varying local strain on few-layer MoS 2 bubbles can lead to an increasing PL intensity from the center of the bubble to the edge due to the strain-induced indirect to direct bandgap transition, which greatly extends the application of these materials in optoelectronic devices 67 (Fig. 3a-d).…”

“…72 Meanwhile, although similar lattice and electronic structural evolutions can be achieved in ultrathin TMDs through uniaxial and biaxial strain, biaxial strain should be more effective in modifying the lattice and electronic structure of ultrathin TMDs when compare to uniaxial strain. 44,63 For instance, a band gap transition from K-S min to G-S min is expected to occur at a much larger uniaxial compressive strain when compared to the biaxial compression strain. 73 A semiconductor to metal transition in monolayer MX 2 can be obtained more easily by application of biaxial tensile strain when compared to the uniaxial strain due to the overlapping of d z 2 orbital at Fermi level.…”

Exciton physics and device application of two-dimensional transition metal dichalcogenide semiconductors

“…Furthermore, one can use strain as a tool to change the relative spectral position of excitons and this way tune the coupling between dark and bright excitonic states [78].…”