懸浮多層二硫化鉬元件製作與傳輸特性

Fabrication and transport properties of suspended few-layer MoS2 devices

劉仕卿(Shih-Ching Liou)

指導教授 ： 梁啟德

共同指導教授 ： 王偉華(Wei-Hua Wang)

國立臺灣大學/理學院/物理研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.01612

摘要

二維材料領域最近轉向研究具有半導體性的過渡金屬硫族化物（TMD）。因其具有高電流開關比（on/off ratio），高電子遷移率（mobility）以及直接能隙（intrinsic bandgap）等特性，使此種材料對未來光電科技應用上的重要性逐漸增加。在本篇論文中，我們探討懸浮結構的過渡金屬硫族化物—二硫化鉬（MoS2）的傳輸特性。之前的研究結果顯示，以二硫化鉬為材料所製成的場效電晶體（field-effect transistor）其電子遷移率遠小於理論預期且其具有表面缺陷（trap state）。造成這些結果部分原因可能是基板的效應包含了游離帶電雜質（charged impurity）與基板表面懸浮鍵（dangling bond）。在此，為了排除基板效應，我們製作懸浮多層二硫化鉬以探討其本質的傳輸特性。我們提供了兩種不需要化學蝕刻步驟且不會有化學殘留製做懸浮元件的方法。第一種為剝離法（exfoliating method），用機械剝離法將二硫化鉬貼在事先蝕刻好溝槽的基版上。第二種為轉映法（transfer method），用聚二甲基矽氧烷（PDMS）軟片將二硫化鉬轉映在事先定義好的電極上。結果顯示，懸浮的元件會比有基板支撐的元件具有較高的電子遷移率，電導和較低的次臨界擺幅（subthreshold swing）。這些結果也顯示了基板對二硫化鉬傳輸特性有重要的影響。更重要的是，我們提供了一個快速製造懸浮結構的方法可以用來探討二硫化鉬本質的熱膨脹，機械和光電等特性。

關鍵字

二硫化鉬 ； 懸浮結構 ； 場效電晶體 ； 電子遷移率 ； 次臨界擺幅

並列摘要

Recently, there is great interest in semiconducting transition-metal dichalcogenide (TMD), which is one category of two-dimensional (2D) materials. Due to high on/off current ratio, high mobility, and intrinsic bandgap, TMD-based materials are essential for future electronic and optoelectronic applications. In this thesis, we study the transport properties of suspended molybdenum disulfide (MoS2), which is one of the semiconducting TMD materials. Previous studies of the transport properties in MoS2-based field-effect transistors (FETs) showed that the mobility is significantly lower than theoretical prediction, and the existence of trapping states. Part of the undesirable effects can be attributed to the substrates including charged impurities and dangling bonds on substrate surface. To exclude these substrate effects for approaching intrinsic properties of MoS2, we fabricated suspended few-layer MoS2 devices and studied the transport properties. We employed two different resist-free methods to fabricate suspended MoS2 devices, which require no chemical etching process. First method was to exfoliate MoS2 flakes onto SiO2 substrates with pre-defined trenches and followed by electrode deposition. Second method was to transfer MoS2 flakes by polydimethylsiloxane (PDMS) films onto the pre-defined electrodes. The suspended MoS2 devices exhibit higher mobility, higher conductance, and lower subthreshold swing, as compared to the controlled MoS2 devices which are SiO2-supported. These results suggest that substrate effect play a critical role on carrier transport of MoS2-based FETs. Moreover, we have demonstrated a feasible method to fabricate suspended MoS2 devices for the investigation of its intrinsic thermal, mechanical, optical, and optoelectronic properties.

並列關鍵字

MoS2 ； suspended ； field-effect transistor ； mobility ； subthreshold swing

參考文獻

2 M. Chhowalla, H. S. Shin, G. Eda, L. J. Li, K. P. Loh, and H. Zhang, "The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets," Nature chemistry 5 (4), 263-275 (2013).

4 B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti, and A. Kis, "Single-layer MoS2 transistors," Nature nanotechnology 6 (3), 147-150 (2011).

5 Z. Yu, Y. Pan, Y. Shen, Z. Wang, Z. Y. Ong, T. Xu, R. Xin, L. Pan, B. Wang, L. Sun, J. Wang, G. Zhang, Y. W. Zhang, Y. Shi, and X. Wang, "Towards intrinsic charge transport in monolayer molybdenum disulfide by defect and interface engineering," Nature communications 5, 5290 (2014).

6 D. Akinwande, N. Petrone, and J. Hone, "Two-dimensional flexible nanoelectronics," Nature communications 5, 5678 (2014).

7 T. Cao, G. Wang, W. Han, H. Ye, C. Zhu, J. Shi, Q. Niu, P. Tan, E. Wang, B. Liu, and J. Feng, "Valley-selective circular dichroism of monolayer molybdenum disulphide," Nature communications 3, 887 (2012).