Photo-Electronic Investigation of MoS₂ Thin-Film Transistors
H. Y. Zhang1*, K. C. Lee1, T.-S. Lim2, L. C. Li3, Y. W. Suen1,4
1Department of Physics, National Chung Hsing University, Taichung, Taiwan, R. O. C., Taiwan
2Department of applied physics, Tunghai University, Taichung, Taiwan, R. O. C., Taiwan
3Center for Nano Science and Technology, National Chiao Tung University, Hsinchu, Taiwan, R. O. C., Taiwan
4Institute of Nanoscience and Nanotechnology, National Chung Hsing University, Taichung, Taiwan, R.O.C., Taiwan
* presenting author:Hong-Yi Zhang,
We investigate the spatial photocurrent distribution of natural molybdenum disulfide based thin film transistors (MoS₂ FETs) by scanning photocurrent technique with a sample stage scanner. The few-layer MoS₂ flakes were obtained by mechanical exfoliation method with a Polydimethylsiloxane (PDMS) film tape, and the thickness was estimated by AFM and Raman spectroscopy. The electrodes (10/90 nm Ti/Au) of MoS₂ FETs were defined by e-beam lithography. A 633-nm wavelength laser was used as the excitation source and the spot size on the focal plane (the sample surface) is about 1.5 μm. The position step of the sample scanner for the areal mapping and line scan are about 100 and 50 nm, respectively. The mapping results show that the photocurrent exhibits a peak near the MoS₂ /metal junction and the peak intensity is not uniform along the junction line. As the line scan profile across the source and drain shown, the photocurrent near the drain and source contacts varies with source-drain and backgate biases. Moreover, the direction of photocurrent near the source side is opposite to that near the drain side. The direction-reversal point of the photocurrent, which indicates the location with zero lateral electric field, moves as the bias changes. The relation between the photo-excitation power and the intensity of peak photocurrent implies that some of the photo-excited electrons and holes recombine before they can be separated to form photocurrent.

Keywords: MoS₂, Photocurrent , Transistors, TMD