Probing the Optical Properties and Strain-Tuning of Ultrathin MoW Te.

Ultrathin transition metal dichalcogenides (TMDCs) have recently been extensively investigated to understand their electronic and optical properties. Here we study ultrathin MoWTe, a semiconducting alloy of MoTe, using Raman, photoluminescence (PL), and optical absorption spectroscopy. MoWTe transitions from an indirect to a direct optical band gap in the limit of monolayer thickness, exhibiting an optical gap of 1.10 eV, very close to its MoTe counterpart. We apply tensile strain, for the first time, to monolayer MoTe and MoWTe to tune the band structure of these materials; we observe that their optical band gaps decrease by 70 meV at 2.3% uniaxial strain. The spectral widths of the PL peaks decrease with increasing strain, which we attribute to weaker exciton-phonon intervalley scattering. Strained MoTe and MoWTe extend the range of band gaps of TMDC monolayers further into the near-infrared, an important attribute for potential applications in optoelectronics.