- 學位論文
藉由電阻映射單層石墨烯之能帶結構
Band structure mapping of monolayer graphene via electrical resistance
摘要
石墨烯是近年來被大量結合於其他半導體材料，因其在二維材料中非常具有潛力之材料，故被大量研究及探討，而本論文探討的目的為以簡易的方式了解其與矽基板組合後之能帶結構圖，相較於其他探討能帶結構之方式簡單上許多，像是使用第一原理所計算出能帶結構，並且了解經濕式轉移(wet transfer)後之石墨烯會因與水中氫氧根結合後轉變為P型摻雜之石墨烯，我們透過的方式是使用閘極調變去檢驗其為N型摻雜或P型摻雜，轉變為P型摻雜後，費米能階(fermi level)會從狄拉克點(dirac point)下降至價帶(valence band)，載子濃度(carrier concentration)也會因轉變為P型摻雜後有所改變。 我們希望感應出更多的電荷而選擇在P型矽基板及N型矽基板上成長非常薄之氧化層，厚度2.7nm左右，成長氧化層後，我們再去蒸鍍出電極，並且確認氧化層具有優異之絕緣效果，也就是具有非常小之漏電流，N型矽基板及P型矽基板所製程元件電阻率約為1015Ω•cm，因若漏電流太大會影響利用閘極調變之結果，轉移石墨烯至基板上後結構為石墨烯/二氧化矽/矽(Graphene/SiO2/Si)，並增加背電極，來對類似MOS電容之結構進行閘極調變，在到達電阻最大值時為狄拉克點，因此時的狀態密度(density of state)為最小值，而會使電阻值上升至最大點，再增大閘極電壓時，在石墨烯端會相對感應出電子，電阻會下降表費米能階往導帶方向移動，由此確認經濕式轉移後轉變為原生P型摻雜。 最後經公式計算得到石墨烯之能帶結構，與經第一原理計算出石墨烯之能帶結構中之導帶變化速度與價帶變化速度不同相符，且因使用之氧化層較薄使得矽基板會影響石墨烯，使得N型矽基板及P型矽基板得到之能帶結構有所差異，且導帶及價帶變化也不同。
並列摘要
Graphene has been extensively combined with other semiconductor materials in recent years. Because of its potential in two-dimensional materials, it has been extensively studied and discussed. This paper aims to understand the energy band structure diagram after combining it with the silicon substrate in a simple way. Compared with other methods of exploring the energy band structure, it is much simpler, such as using the first principle to calculate the energy band structure. And it is understood that the graphene after the wet transfer will be converted into P-type doped graphene due to the combination with hydroxide in water. The way we pass is to use gate modulation to test whether it is N-type doping or P-type doping. After switching to P-type doping, the Fermi level will drop from the Dirac point to the valence band. The carrier concentration will also change due to the transition to P-type doping. We hope to induce more charges and choose to grow a very thin oxide layer on the P-type silicon substrate and N-type silicon substrate, with a thickness of about 2.7nm. After growing the oxide layer, we evaporate the electrode and confirm that the oxide layer has an excellent insulating effect, that is, it has a very small leakage current. The resistivity of the N-type silicon substrate and P-type silicon substrate is about 1015Ω•cm. If the leakage current is too large, the result of gate modulation will be affected. After transferring graphene to the substrate, the structure is graphene/silicon dioxide/silicon (Graphene/SiO2/Si), like a MOS capacitor, and a back electrode is added. Then perform gate modulation. When it reaches the maximum resistance value, it is the Dirac point, so the density of the state is the minimum value, and the resistance value will rise to the maximum point. The graphene end will be relatively induced when the gate voltage increases. When electrons are taken out, the resistance will drop and the Fermi level will move to the conduction band direction, thus confirming that it is converted to native P-type doping after wet transfer. Finally, the energy band structure of graphene is calculated by the formula, which is different from the change speed of the conduction band and the change speed of the valence band in the energy band structure of graphene calculated by the first principle, and the silicon substrate will be thinner due to the thin oxide layer used. Affecting graphene, the energy band structures obtained from the N-type silicon substrate and the P-type silicon substrate are different, and the conduction band and valence band change are also different.