過渡金屬硫屬化物薄膜電晶體:晶粒尺寸與摻雜效應

Abstract

二維層狀材料如石墨烯被成功製備之後，驗證了單原子層材料能穩定存在，開啟了研究二維材料的熱潮。石墨烯擁有許多吸引人的特性，目前已有不少應用石墨烯的產品如觸控螢幕及電池等，但其特殊的能帶結構使得石墨烯不適合應用在邏輯元件上，在許多被廣泛研究的二維材料中，過渡金屬硫屬化物被視為具有潛力應用在奈米電子元件或光電元件上，成為下一代電晶體的主要材料。 然而這類材料是否能應用於未來電子產品取決於這些薄膜的品質於元件特性，因此本篇論文主要利用李連忠教授實驗室的大面積化學氣相沉積系統製備大面積的過渡金屬硫屬化物薄膜及利用張文豪教授實驗室的光學量測系統觀察薄膜的品質及特性，搭配元件的製程(於國立交通大學奈米中心及國家奈米元件實驗室)，目的在觀察這類材料的晶粒大小及摻雜對於電晶體特性的影響，進而提出改善的方式。 本篇論文分析了不同晶粒大小的單層二硫化鉬電晶體特性，並利用非破壞性的光學量測輔助觀察，統計出元件特性與薄膜晶粒大小的關係，提出可以由增加薄膜的晶粒大小作為改善電晶體特性的出發點。然而未盡理想的元件特性使得我們必須思考薄膜的導電特性及接觸電阻問題，因此我們觀察二硫化鉬及二硒化鎢薄膜轉移(transfer)過程中的摻雜現象，並試圖利用缺陷的產生(電漿處理)來改善元件的特性及接觸電阻，搭配不同基板的效應，達到較好的單層二硫化鉬電晶體特性。雖然相關的研究如不同基板對薄膜成長及元件特性的影響尚未完全的瞭解，但是本篇論文給出了改善元件特性的大方向，為將來相關實驗奠定了有效的分析工具及方法。

The successful synthesis of graphene demonstrates the stability of two-dimensional (2D) materials with an atomic thickness, and inspires strong interests on the research of 2D materials. Several commercial products, such as touch screen and battery, have taken advantages of the attractive properties of graphene. However, the unique gapless band structure of graphene makes it unsuitable for logic circuit applications. Among various 2D materials, transition metal dichalcogenides (TMDs) with finite bandgap values are promising as the next-generation channel materials of the transistor for nanoelectronic and photoelectronic applications. The property of the TMD films and their device characteristics are the key point to evaluate the potentials of 2D TMDs. We used the chemical vapor deposition system at the Prof. Lain-Jong Li’s group to synthesize large-scale TMD films and analyzed their quality and property by using various optical techniques at the Prof. Wen-Hao Chang’s group. Final, the TMD thin film transistors (TFTs) were fabricated at Nano Facility Center, National Chiao Tung University and National Nano Device Laboratories. The objective of this study is to evaluate the grain size and doping effect on transistor characteristics, and provides a general guideline to improve device performance. In this thesis, we analyzed the grain size effect of the monolayer MoS2 TFT, and used the nondestructive second harmonic generation (SHG) measurement to characterize the grain size. The statistics of device performance correlate well with the grain size, suggesting that the device performance can be further improved by enlarging the grain size. However, we also observed that the poor device electrical characteristics, which are depended strongly on the contact resistance and the doping of TMDs. We examined the doping effect before and after transferring MoS2 and WSe2, and used the defect generation (by plasma treatment) and different hosting substrates of transferred films to improve the device performance and reduce the contact resistance. Although the different hosting substrate effect on film synthesis and device performance are still under investigation, this thesis points out useful directions and provides effectives analysis techniques and methodology.