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  • 學位論文

反應氣氛對化學氣相沉積法於銅基板上成長石墨烯之影響

Influence of the Reaction Gases on Graphene Growth on Copper Substrates by Chemical Vapor Deposition

指導教授 : 溫政彥

摘要


石墨烯為一由含有sp2鍵結的碳原子所構成之六角碳環組成的二維平面材料,由於其優異的電子性質以及機械性質,使得石墨烯在近年來引起許多學者們的注意,並且紛紛投入其研究。為了於未來將石墨烯應用於各式各樣的電子元件上,具備穩定且能生產出高品質石墨烯的製備方法是非常關鍵的因素,而在眾多製備石墨烯的方法當中,利用化學氣相沉積法進行石墨稀成長,相較於其他製備方法有著許多優點,它包含了製程簡單以及可以控制石墨烯薄膜的層數,除此之外最重要的是化學氣相沉積法能將其製程規模放大,有利於業界進行大面積的生產,以達商業化之目標,然而利用化學氣相沉積法所製備的石墨烯薄膜,其品質至今仍遠不及機械剝離法,主要原因在於利用化學氣相沉積法成長石墨烯薄膜時,在石墨烯薄膜的晶界處含有大量缺陷,導致其薄膜的載子遷移率降低,連帶影響了石墨烯電子元件的效率。因此若要有效地減少這些晶界在石墨烯薄膜的分布,則必須先減少石墨烯在成長初期的成核密度,以降低在石墨烯薄膜中的缺陷密度,使利用石墨烯所製備的元件之效率得以提升。在本論文中,我們探討了化學氣相沉積製程中的反應氣氛對石墨烯薄膜成長的影響,並且在進行石墨烯成長之前,先將金屬銅基板置於氧氣氣氛下,使其表面產生穩定的氧化層,而能有效地鈍化銅金屬表面的成核點,使石墨烯在成長初期階段的成核密度可以從104 nuclei/mm2降低至3 nuclei/mm2,石墨烯的晶域大小也因此得以從十微米提升至釐米等級;而經由石墨烯電晶體的電子性質量測,也驗證了石墨烯晶域大小的增加,可以降低含有缺陷結構的晶界分布,提升了石墨烯薄膜的品質,其載子遷移率可以從1500 cm2/V s 上升至3270 cm2/V s;而當選用具有高化學活性的乙炔氣體為碳源進行石墨烯薄膜成長時,其成長溫度可以從1000℃大幅地降低至750℃,使得其石墨烯成長較能相容於現今的半導體製程技術。

並列摘要


Graphene, a two-dimensional hexagonal lattice structure composed of sp2-bonded carbon atoms, has drawn significant attention for its exceptional electrical and mechanical properties. In order to apply graphene in electronic devices, reliable fabrication methods, which can produce high-quality graphene layers, are very essential. Among the approaches to synthesize graphene, the chemical vapor deposition (CVD) method shows several advantages, including simple fabrication procedures, easy control of graphene layer numbers, and, most importantly, its scalability – it has been demonstrated that the size of graphene sheet is large enough for industrial applications. However, the quality of CVD-grown graphene is not comparable with those exfoliated from graphite flakes; the defects, such as the domain boundaries, degrade the carrier mobility in graphene. Therefore, reducing the amount of domain boundaries by means of reducing the nucleation density in the initial stage of graphene growth will be beneficial for improving the electrical properties of graphene-based devices. In this study, we investigate the effects of the reaction gases in CVD graphene growth on the nucleation density. We find that the presence of oxygen prior to graphene growth leads to the formation of copper oxide layers on Cu substrate that passivate the active sites for nucleation, greatly reducing the nucleation density from 104 to 3 nuclei/mm2. Due to the passivation, the graphene domain size increases from 10 μm to 1 mm; the carrier mobility of graphene field effect transistor is increased from 1500 cm2/V s to 3270 cm2/V s, therefore improving the quality of graphene films. When high-reactivity acetylene is used as the carbon source, the growth temperature can be dramatically reduced from 1000℃ to 750℃, making the CVD growth more compatible with the existing semiconductor fabrication processes.

參考文獻


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