二維材料及其異質結構之成長及應用

2D Materials and Their Hetero-structures

吳崇榮(Chong-Rong Wu)

指導教授 ： 吳肇欣

國立臺灣大學/電機資訊學院/電子工程學研究所/博士(2018年)

https://doi.org/10.6342/NTU201802097

摘要

本論文聚焦在二維材料 (2D Material) 的成長及其異質結構 (Hetero-structure) 在元件上的應用，在材料方面，主要研究對象為石墨烯 (Graphene) 、過渡金屬二硫化物如二硫化鉬 (MoS2) 以及二硫化鎢 (WS2) ，首先我們致力於薄膜大面積化成長及達成層數 (Layer number) 的可控制性，我們利用傳統的化學氣相沉積法成功製備出大面積石墨烯和二硫化鉬薄膜，並提出重複成長來取代調整前驅物重量的方式達到精準的層數控制，再取用所成長之薄膜製備成電晶體元件。雖然化學氣相沉積法已被證明是一種快速及簡單的方式來成長大面積的二維材料，然而，在基板上的選擇性成長對此成長方式仍是一大挑戰。我們運用硫化預先鍍好的過渡金屬薄膜的方式來成長大面積的過渡金屬二硫化物薄膜如二硫化鉬以及二硫化鎢於藍寶石基板，我們同時也利用過渡金屬的選擇性沉積來達成了過渡金屬二硫化物的選擇性成長，除了選擇性成長之外，此成長技術最大的優勢在於可運用相同的硫化條件來製備不同的過渡金屬二硫化物薄膜。透由接續的金屬沉積以及硫化的步驟，我們可構建出可控層數的二硫化鎢/二硫化鉬異質結構，由於在 type-II 的二硫化鎢/二硫化鉬異質結構中，電子會由二硫化鎢注入至二硫化鉬通道層，因此相較於二硫化鉬電晶體，二硫化鎢/二硫化鉬異質結構具有較高的汲極電流及遷移率，這些結果也顯示出透過將不同的二維材料堆疊成異質結構，單一二維材料的元件特性瓶頸可以被突破，由此可看出二維材料異質結構的發展對二維材料進入實用的領域實有極大的幫助。

關鍵字

二維材料 ； 過渡金屬二硫化物 ； 二維材料異質結構 ； 場效電晶體 ； 化學氣相沉積

並列摘要

In this thesis, we focused on the fabrication of 2-D materials and their hetero-structures for device applications. The main research materials are graphene and transition metal disulfides, such as MoS2 and WS2. At the beginning, we dedicated to the growth of large-area films and the layer number controllability of individual 2D materials. We have successfully fabricated large-area graphene and MoS2 thin films grown by using the chemical vapor deposition (CVD). By changing the precursor amounts, we have demonstrated good layer number controllability by using CVD. Besides the direct control of precursor amounts, we have also proposed the approach of repeating the same CVD growth cycle to control the layer numbers of the grown 2D materials. Although CVD has been proved to be a quick and easy approach for large-area 2D materials, selective growth is still a challenge for this technique. We have demonstrated that by sulfurizing pre-deposited transition metal films, large-area transition metal disulfides such as MoS2 and WS2 can be grown on sapphire substrates. Selective growth of the 2D materials can also be achieved by selectively depositing the transition metals on the sapphire substrates. Besides the selective 2D material growth, the major advantage of this technique is that the same sulfurization procedure can be applied to different transition metal disulfides. Trough sequential metal deposition and sulfurization procedures, layer-number-controllable WS2/MoS2 hetero-structures can be established. Compared with standalone MoS2 transistors, the electron injection from the WS2 layer to the MoS2 channel would lead to a higher drain current and mobility value for the type-II WS2/MoS2 hetero-structure transistor. The results have demonstrated that the limitation of individual 2D materials may be overcome by stacking the materials onto each other to form hetero-structures, which will be advantageous for practical application.

並列關鍵字

2D materials ； Transition metal disulfides ； 2D material hetero-structures ； field-effect transistors ； chemical vapor deposition

參考文獻

1. J. X. Zheng, L. Wang, R. G. Quhe, Q. H. Liu, H. Li, D. P. Yu, W. N. Mei, J. J. Shi, Z. X. Lu, "Sub-10 nm Gate Length Graphene Transistors: Operating at Terahertz Frequencies with Current Saturation", Sci. Rep., vol. 3, pp. 1314, February 2013.

2. M. Y. Lin, C. H. Wang, S. W. Chang, S. C. Lee, and S. Y. Lin, "Passivated graphene transistors fabricated on a millimeter-sized single-crystal graphene film prepared with chemical vapor deposition", J. Phys. D, Appl. Phys., vol. 48, no. 29, July 2015.

3. K. Alam and R. K. Lake, "Monolayer MoS2 Transistors Beyond the Technology Road Map", IEEE T Electron Dev., vol. 59, no. 3250–3254, November 2012.

4. K. S. Novoselov, V. I. Fal'ko, L. Colombo, P. R. Gellert, M. G. Schwab, and K. Kim, "A roadmap for graphene", Nature, vol. 490, pp. 192-200, October 2012.

5. Q. H. Wang, K. Kalantar-Zadeh, A. Kis, J. N. Coleman and M. S. Strano, "Electronics and optoelectronics of two-dimensional transition metal dichalcogenides", Nat. Nanotechnol., vol. 7, pp. 699–712, November 2012.