Valley polarization and photocurrent generation in transition metal dichalcogenide alloy MoS2xSe2(1−x)

Monolayer transition metal dichalcogenides (TMDCs) constitute the core group of materials in the emerging semiconductor technology of valleytronics. While the coupled spin-valley physics of pristine TMDC materials and their heterostructures has been extensively investigated, less attention has been given to TMDC alloys, which could be useful in optoelectronic applications due to the tunability of their band gaps. The experimental investigations presented herein focus on the exploration of the spin-valley physics of the monolayer and bilayer TMDC alloy ${\mathrm{MoS}}_{2x}{\mathrm{Se}}_{2(1\ensuremath{-}x)}$ in terms of valley polarization and the generation as well as electrical control of a photocurrent utilizing the circular photogalvanic effect. Piezoelectric force microscopy provides evidence for an internal electric field perpendicular to the alloy layer, thus breaking the out-of-plane mirror symmetry. The experimental observation is supported by first-principles calculations based on the density functional theory. A comparison of the photocurrent device, based on the alloy material, is made with similar devices involving other TMDC materials.