Scalable Deposition of MoS2 Thin Films with Controlled Doping for Photodetectors

Abstract

Molybdenum disulfide (MoS₂), the most widely explored transition metal dichalcogenide, is a promising candidate for developing high-performance photodetectors due to having a wide range of electric and optoelectronic properties. However, the controlled synthesis of a highly crystalline large-area MoS₂ thin film and the effect of noble metal (Au, Ag) nanoparticles and TM (Co) ion doping on its photoelectrical properties are still challenging. Herein, we report the direct growth of wafer-scale MoS₂ thin films utilizing a facile polymer-free approach by a solution-phase coating process, followed by thermal annealing. A systematic study on the photoelectrical properties of the Au-, Ag-, and Co-doped (all variants are in 10 at. wt %) MoS₂ photodetectors reveals that the Co-MoS₂ device exhibits excellent photoresponse properties, which are also evidenced theoretically. Moreover, the Co-dopant amount is varied (5, 20 at. wt %) to decipher the impact of Co-doping on the photoresponse properties and determine the optimum doping percentage. The highest (20 at. wt %) Co-doped MoS₂ photodetector exhibits good photoresponse characteristics at low voltage with minimal noise and high stability (retaining 86% of its photoresponsivity after the 30th day), attributed to the long-lived trap states, the photogating effect, more n-type doping, and generation of more charge carriers. Interestingly, the variations in Co-dopant concentrations lead to tunable photoresponse in different (blue, green, and red) laser illuminations, attributed to the band gap tunability with variable doping. This simple TM doping approach proposed in this study for improving the performance of MoS₂ photodetectors can open up an avenue for research for other 2D materials, finding potential applications in photodetection and low-voltage-based operating devices.