Dichroic spin–valley photocurrent in monolayer molybdenum disulphide

Abstract

The aim of valleytronics is to exploit confinement of charge carriers in local valleys of the energy bands of semiconductors as an additional degree of freedom in optoelectronic devices. Thanks to strong direct excitonic transitions in spin-coupled K valleys, monolayer molybdenum disulphide is a rapidly emerging valleytronic material, with high valley polarization in photoluminescence. Here we elucidate the excitonic physics of this material by light helicity-dependent photocurrent studies of phototransistors. We demonstrate that large photocurrent dichroism (up to 60%) can also be achieved in high-quality molybdenum disulphide monolayers grown by chemical vapour deposition, due to the circular photogalvanic effect on resonant excitations. This opens up new opportunities for valleytonic applications in which selective control of spin–valley-coupled photocurrents can be used to implement polarization-sensitive light-detection schemes or integrated spintronic devices, as well as biochemical sensors operating at visible frequencies.

Photodetectors based on junctions of two-dimensional transition metal dichalcogenides

“…[118] By circularly polarized optical pumping, ( Vertical heterojunction) and transfer photovoltaic 3.1 NA NA NA [106] spin-valley coupled polarization can be generated, [119] which has been observed in optoeletronic devices based on MoS2 [120] and WSe2. [121,122] It should be of great significance to introduce spin-polarization and valley-polarization in photodetectors based on junctions of TMDCs.…”

Optoelectronic Devices Based on Atomically Thin Transition Metal Dichalcogenides

“…The sign of the Hall voltage could be controlled by the helicity of the light, whereas there was no effect detectable for linearly polarized light or (inversion-symmetric) bilayer devices. Other studies demonstrated a valley dependent photodetector in CVD grown MoS 2 [115] and the generation of spin-valley-coupled circular photogalvanic currents in WSe 2 [116]. Zhang et al [65] fabricated a chiral light-emitting transistor by forming a multi-layer WSe 2 p-n junction using electric double layer gating.…”

Engineering Valley Polarization of Monolayer WS2: A Physical Doping Approach

“…This property enables selectively pumping + K (− K ) valley with left (right) hand circular light excitations to create an imbalanced carrier population between two valleys. Realizing such net valley polarization is an essential step for developing valleytronic devices . Resulted from the opposite selection rules of two valleys, controlling valley polarization in mono‐layer TMDs by optical helicity is achievable.…”