Photocurrent Distribution of a Multilayer MoS₂ Device
K. C. Lee1*, L. C. Li2, Y. W. Suen1,3
1Department of Physics, National Chung Hsing University, Taichung, Taiwan
2Center for Nano Science and Technology, National Chiao Tung University, Hsinchu, Taiwan
3Institute of Nanoscience and Nanotechnology, National Chung Hsing University, Taichung, Taiwan
* presenting author:李國誌,
We used a confocal microscope to map the photoresponse of a molybdenum disulfide thin film transistor (MoS₂ FET). The device was fabricated by a standard mechanical exfoliation method and e-beam lithography with 20 nm Ti/50 nm Au electrodes. The layer number of the MoS₂ flake is 6 identified by optical microscopy, atomic force microscopy and Raman spectroscopy. The length and the average width of the FET device are 4.5 μm and 3 μm, respectively. The field-effect mobility is about 3.6 cm²/Vs in the air and 5.6 cm²/Vs in vacuum at room temperature. The photocurrent was measured at a back-gate bias of 20V with a 633 nm-wavelength laser excitation source with a power of 14 μW and a spot size of 1.5 μm. The step resolution of the scanning stage is 3 nm. The photocurrent map shows a large photo response near the source electrode. This result can be explained by the bias induced band bending near the Schottky barrier. We also investigate the photo switching behavior during the on/off periods of laser. The decaying part of the transient response can be separated into three parts with different decay time constant. The sudden drop at the beginning of the decaying response can be attributed to the fast recombination of electrons and holes. The second region before 100 s may be due to the thermal effect with a time constant of about 20 s. The last decaying region after 100 s can be explained by the slow charge traps at the MoS₂ surface with a time constant of about 1300 s.

Keywords: molybdenum disulfide, photoresponse