Promoting the Performance of Layered-Material Photodetectors by Alloy Engineering

The successful peeling of graphene heralded the era of van der Waals material (vdWM) electronics. However, photodetectors based on semiconducting transition metal dichalcogenides (TMDs), formulated as MX2 (M = Mo, W; X = S, Se), often suffer either poor responsivity or long response time because of their high density of deep-level defect states (DLDSs). Alloy engineering, which can shift the DLDSs to shallow-level defect states, is proposed to be an efficient strategy to solve this problem. However, proof-of-concept is still lacking, which is probably because of the absence of a facile technology to grow high-quality alloyed TMDs. Here, we report the growth of large-scale and high-quality Mo0.5W0.5S2 alloy films via pulsed laser deposition (PLD). We demonstrate that the resulting Mo0.5W0.5S2 photodetector possesses a stable photoresponse from 370 to 1064 nm. The photocurrent exhibits positive dependence on both the source-drain voltage and incident power density, providing good tunability for multifunctional photoelectrical applications. We also establish that, because of the suppression of DLDSs with alloy engineering, the Mo0.5W0.5S2 photodetector achieves a good responsivity of 5.8 A/W and a response time shorter than 150 ms. The working mechanism for the suppression of DLDSs in Mo0.5W0.5S2 is unveiled by qualitatively analyzing the alloying-dressed band structure. In conclusion, the excellent performance of the PLD-grown Mo0.5W0.5S2 photodetector may pave the way for next-generation photodetection. The approach shown here represents a fundamental and universal scenario for the development of alloyed TMDs.