透明可撓式二氧化鈦與氮摻雜二氧化鈦摻雜石墨烯場效電晶體之研究

Investigation on the TiO2 and N-doped TiO2 -doped Graphene for Synthesizing Flexible Transparent Field Effect Transistor

吳昱賢

指導教授 ： 戴念華

國立清華大學/工學院/材料科學工程學系/碩士(2014年)

https://doi.org/10.6843/NTHU.2014.00370

摘要

石墨烯(Graphene)為一單層碳原子材料，具有特殊的光學與電學性質、優良的化學穩定性以及高載子遷移率，這些獨特的性質，使石墨烯具備取代矽材料作為電子元件的潛力。此外，如藉由不同物質之摻雜，遂可改變石墨烯的傳導特性，而可製作出P型或N型場效電晶體。故本研究以熱化學氣相沉積系統於電解拋光銅箔上成長大面積的單層石墨烯，並轉印至可撓高分子聚對苯二甲酸乙二酯(Polyethylene terephthalate, PET)基板上，以製作可撓性透明場效電晶體；並利用二氧化鈦與氮摻雜二氧化鈦奈米顆粒對石墨烯進行摻雜，以改變石墨烯的電性與提高石墨烯的載子遷移率，並使其具有紫外光與可見光的感光特性。研究中使用拉曼光譜儀、光學顯微鏡、場發射電子顯微鏡探討實驗參數對石墨烯成長及轉印結果的影響，並以紫外光-可見光光譜儀分析石墨烯的吸光率，及原子力顯微鏡量測單層石墨烯的厚度。另一方面，利用X光繞射儀與光致發光光譜儀鑑定二氧化鈦與氮摻雜二氧化鈦奈米顆粒的基本物性，並以化學分析電子能譜儀分析氮摻雜二氧化鈦之化學鍵結與元素含量。在場效電晶體量測上，以多探針量測系統量測元件之電學性質，並探討紫外光與可見光光源照射及彎曲條件對電性之影響。
研究結果顯示，於電解拋光銅箔上成長之單層石墨烯，其厚度、吸光率與載子遷移率分別為0.4-0.7 nm、2.39%與1900 cm2/V∙s。經二氧化鈦與氮摻雜二氧化鈦(氮含量：1.4 at.%)摻雜後，其呈現出N型摻雜的效果，且分別使石墨烯載子遷移率提升至53000 cm2/V∙s與31000 cm2/V∙s。進一步透過紫外光與可見光照射可發現，由於二氧化鈦與氮摻雜二氧化鈦內電子-電洞對之產生，激發電子可傳遞至石墨烯通道中，而呈現N型傳導特性；於照射後，電性可於5分鐘內回復至初使狀態，故證實摻雜後此電晶體元件亦兼具紫外光與可見光之感測性。在撓曲測試上，其結果顯示當曲率半徑大於2.0 cm時，載子遷移率無明顯變化。

關鍵字

石墨烯 ； 透明可撓電晶體 ； 二氧化鈦 ； 光感測

並列摘要

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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