二硫化鎢鈮的合成與其凡得瓦異質結構的電性傳導機制探討

Synthesis and electrical transport mechanism of NbxW1-xS2 van der Waals heterostructures

彭偉皓(Wei-hao Peng)

指導教授 ： 呂明諺

國立清華大學/工學院/材料科學工程學系/碩士(2020年)

摘要

本研究旨在探討二硫化鎢（WS2）的場效電晶體元件中，我們首先合成二硫化鎢鈮（NbxW1-xS2）並以此材料與WS2形成以凡得瓦力（van der Waals Force）堆疊之NbxW1-xS2-WS2異質結構元件，此有利於實現本質為N型半導體的WS2呈現P型傳導的電流表現，並進一步探討其傳導機制。
首先，我們利用化學氣相傳輸法合成NbxW1-xS2的塊材，接著透過機械剝離法將材料分離成數十奈米厚的二維薄片狀材料，並以乾式轉印法將之轉移到二氧化矽/矽基板上，緊接著透過電子束微影系統及電子束蒸鍍系統定義出電極，完成元件的製作。
材料分析方面，我們透過光學顯微鏡和掃描式電子顯微鏡觀察材料表面形貌，再利用顯微拉曼光譜儀了解其原子振盪模式，接著以X光光電子能譜儀對材料進行化學組成分析，最後使用X光繞射儀與穿透式電子顯微鏡對材料的晶體結構與原子分佈做更進一步的探討與分析。
在NbxW1-xS2-WS2凡得瓦異質結構元件中，我們透過四點探針系統進行電性量測與分析，得到異質結構元件出現具P型半導體特性的電性表現。接著，我們透過表面電位顯微鏡進一步分析材料的功函數以及重建此一元件結構的電子能帶圖，並輔以變溫電性量測系統萃取材料與電極之間的蕭特基能障，以探討此NbxW1-xS2-WS2凡得瓦異質結構的特性，進一步說明其載子傳導的機制。最後，本研究將有助於互補式場效電晶體、二維接觸電極材料等應用，以解決現今二維半導體材料的研究中尚缺乏穩定之P型傳導材料的瓶頸。

關鍵字

二維材料 ； 過渡金屬二硫族化合物 ； 二維金屬 ； 二硫化鎢鈮 ； 凡得瓦異質結構

並列摘要

In the past years, two-dimensional (2D) transition metal dichalcogenide (TMD) materials have attracted numerous attentions for next-generation nanoelectronics applications due to their unique electrical and physical properties. However, the technical solution regarding how to reliably obtain the p-type 2D field-effect transistor (FET) is still under investigation, thus limiting the applications of 2D FETs in CMOS circuits.
In this report, we synthesized the NbxW1-xS2 flake and further demonstrated that the 2D NbxW1-xS2 flake is beneficial for the realization of p-type 2D FET after forming the heterostructures with WS2. The chemical vapor transport (CVT) method was used to synthesize large-scale NbxW1-xS2 flakes. The thickness of the as-grown NbxW1-xS2 and WS2 flakes were thinned down by using the mechanical exfoliation method, followed by the dry transfer method to place the 2D NbxW1-xS2 flake onto the Si/SiO2 substrate. The material characterizations of the large-scale 2D NbxW1-xS2 materials were conducted by using the SEM, Raman spectra, and AFM tools.
The electrical properties of the NbxW1-xS2–WS2 van der Waals heterostructure were explored through the four-point probe system, revealing a p-type characteristic. Then, KPFM and temperature-dependent electrical measurements were conducted to further analyze the transport mechanism through reconstructing the band diagram of the heterostructure and extracting the Schottky barrier height of the device.
Finally, the p-type WS2 FETs were experimentally realized through the NbxW1-xS2–WS2 van der Waals heterostructure. This report paves a way from material synthesis points of view towards modulating the dominantly operational polarity in 2D WS2 FETs for future nanoelectronics applications.

並列關鍵字

TMDs

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