Enhancement of Photodetective Properties on Multilayered MoS(2) Thin Film Transistors via Self-Assembled Poly-L-Lysine Treatment and Their Potential Application in Optical Sensors

Photodetectors and display backplane transistors based on molybdenum disulfide (MoS(2)) have been regarded as promising topics. However, most studies have focused on the improvement in the performances of the MoS(2) photodetector itself or emerging applications. In this study, to suggest a better insight into the photodetector performances of MoS(2) thin film transistors (TFTs), as photosensors for possible integrated system, we performed a comparative study on the photoresponse of MoS(2) and hydrogenated amorphous silicon (a-Si:H) TFTs. As a result, in the various wavelengths and optical power ranges, MoS(2) TFTs exhibit 2~4 orders larger photo responsivities and detectivities. The overall quantitative comparison of photoresponse in single device and inverters confirms a much better performance by the MoS(2) photodetectors. Furthermore, as a strategy to improve the field effect mobility and photoresponse of the MoS(2) TFTs, molecular doping via poly-L-lysine (PLL) treatment was applied to the MoS(2) TFTs. Transfer and output characteristics of the MoS(2) TFTs clearly show improved photocurrent generation under a wide range of illuminations (740~365 nm). These results provide useful insights for considering MoS(2) as a next-generation photodetector in flat panel displays and makes it more attractive due to the fact of its potential as a high-performance photodetector enabled by a novel doping technique.