| Summary: | 碩士 === 國立清華大學 === 材料科學工程學系 === 102 === Graphene, a monolayered carbon material with hexagonal structure, has attracted intensive attention due to its unique optoelectrical properties, excellent chemical stability and high carrier mobility, which shows potential for replacing silicon in semiconductor industry. In addition, by doping various species one could tailor the transfer properties of graphene and construct P-type or N-type field-effect-transistor devices. In this study, large-area and single-layer graphene was grown on the electropolished Cu foil by the thermal chemical vapor deposition method and transferred on a polyethylene terephthalate substrate to fabricate flexible transparent field-effect-transistors. TiO2 and N-doped TiO2 nanoparticles were doped on the graphene to alter the electric properties of graphene, enhance the carrier mobility of graphene and make transistors possess optical sensing of UV and visible light. Graphene growth and transferring were characterized by Raman spectroscopy, field-emission scanning electron microscopy, and optical microscopy; the absorbance and thickness of graphene were measured using UV-Vis spectrophotometer and atomic force microscopy, respectively. On the oher hand, the physical properties of TiO2 and N-doped TiO2 nanoparticles were identified by X-ray diffractometer and photoluminescence spectroscopy, and the chemical bonding and element content of N-doped TiO2 nanoparticles were investigated by ESCA. Electrical properties of the fabricated FETs were examined by a multi-probe system and the influences of irradiation of UV and visible light and bending test on electrical propeties were also analyzed.
The results indicate that the thickness, absorbance, and carrier mobility of the graphene were 0.4-0.7 nm, 2.39%, and 1900 cm2/V∙s, respectively. Doping of TiO2-doped and N-doped TiO2 (N: 1.4 at.%) leads to a N-type doping effect and the carrier mobility of graphene were improved to 53000 cm2/V∙s and 31000 cm2/V∙s, respectively. By UV and visible light irradiation, TiO2 and N-doped TiO2 generated electrons and holes, and the generated electrons transferred to graphene channels, which caused FETs to show N-type electric behavior. Moreover, the electric properties of graphene returned back to their initial state within 5 min, confirming that the graphene FETs showed photosensitive to UV and visible light. Under the bending of the curvature radius higher than 2.0 cm, the carrier mobility of the FETs were not substantially changed.
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