| Summary: | 碩士 === 國立彰化師範大學 === 電子工程學系 === 106 === In this study, we grew large-area molybdenum disulfide (MoS2) thin films by low pressure thermal sulfurization. We evaporated gold (Au, 5.10 eV), silver (Ag, 4.26 eV), and aluminum (Al, 4.28 eV) as metal electrodes with different metal work function.
Scanning electron microscope image reveals continuous thin films on surface, meanwhile, the thickness is approximate 129 nm analyzed by secondary ion mass spectrometer. Raman scattering spectrum shows that the peaks at 374 cm-1 and 402 cm-1 are from MoS2 thin film. X-ray diffraction (XRD) reveals peaks at 33.06o and 58.5o indicating MoS2 (100) and (110) crystal phase.
We investigate Au, Ag, and Al contacts to MoS2 thin film as metal contacts by temperature-dependent I-V curve measurement to estimate the Schottky barrier heights of 64.6 meV, 59.8 meV, and 60.2 meV, respectively. Photocurrent mapping also reveals that Ag contacts have the best carrier transport characteristic with carrier diffusion length of 106 μm.
We also identify that the lower metal work function could form lower Schottky barrier which would inject more charge by TLM, photoconductivity, photoresponse, and impedance measurements. The responsivity can be up to 2.12 mA/W.
Further, we designed 300, 400, 500, and 600-μm contact spacing of MoS2 thin film metal-semiconductor-metal (MSM) photodetectors (PDs) with interdigitated fingers of Ag contacts. The transition between MoS2 and Ag contacts with larger contact spacing reveals the better photoresponsivity range of MoS2 MSM PDs.
In addition, we reduced the vacancy on the surface of MoS2 at different annealing temperature (450 °C, 550 °C, 650 °C, 750 °C) with amount of sulfur. The composition ratio of Mo and S is observed by Energy dispersive spectrometer analysis, and the full width half maximum is about 0.237o which was fitted by XRD peak. Finally, the annealing characteristics indicated that the best annealing temperature was at 550 °C.
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