基於二維過渡金屬二硫屬化物之功能性電子元件的接觸工程與相關策略

Abstract

基於二維過渡金屬二硫屬化物之電子元件的發展被其接觸問題所限制，而原因在於不適當的蕭特基能障高度。費米能級釘扎效應導致無法僅透過金屬功函數的選取去調控蕭特基能障高度，從而阻礙了具有適當障高的高效能二維電子元件的設計。本論文首先回顧過渡金屬二硫屬化物在接觸問題上的挑戰，進一步探討文獻中提出的解決方案，並提出本研究於接觸工程上的策略，旨在實現具特定功能的電子元件。

本論文包含三個實驗部分：第一部分介紹一種用於背閘預先圖樣化接觸之「懸邊」工程策略，應用於過渡金屬二硫屬化物。利用該策略製備的多層二硫化鎢蕭基二極體具有閘極可調性，並在整個閘壓掃描範圍內展現近乎理想的二極體特性，顯示出在單一二維元件中整合整流與閘控功能的潛力。第二部分提出一種針對低維材料的 P 型摻雜方法，藉由將單層二硒化鎢經氧氣電漿處理轉化為氧化鎢。此摻雜方法可提升電洞濃度，進而減薄蕭特基能障寬度，降低接觸電阻。當此氧化鎢轉化方法應用於三層二硒化鎢的 P 型金氧半場效電晶體作為間隔摻雜策略時，元件的效能因接觸區電阻降低而顯著提升。最後一部分聚焦於邊緣接觸，這是一種具有潛力的二維奈米片接觸方案。為了優化邊緣接觸，兩種技術被提出：退火處理與邊緣功能化；轉移特性量測結果顯示兩者分別透過不同機制改善元件效能。結合這兩種技術與通道長度微縮後，成功製備出高效能的短通道邊緣接觸型 P 型場效電晶體元件。

接觸工程仍然是二維過渡金屬二硫屬化物實用化應用的關鍵挑戰，需要持續的研究。本篇論文中提出的策略有助於解決特定應用中的關鍵問題，並為二維電子產品的可擴展生產提供潛在途徑。

Advancements of two-dimensional transition metal dichalcogenides (2D TMDs)-based electronic devices are hindered by contact limitations, stemming from the undesired Schottky barrier height (SBH). Fermi-level pinning prohibits effective tuning of SBH by solely considering metal work function, making it difficult to design functional 2D electronic devices with suitable barrier heights. This dissertation begins with a review of contact issues in TMDs, discusses the proposed solutions in literature, and presents strategies in contact engineering aimed at realizing specific functional electronic devices.

There are three experimental sections in this dissertation: The first introduces an “edge suspension” engineering strategy for back-gated, pre-patterned contacts to TMDs. A multilayer WS2 Schottky diode with the proposed suspension engineering is gate-tunable and exhibits nearly ideal diode characteristics over the whole gate-sweep window, suggesting a promising design for integrating current rectification and gate modulation in a single 2D device. The second section presents a p-doping method for low-dimensional materials via WOx conversion of 1L-WSe2 using O2 plasma. This p-doping effect thins the Schottky barrier width by increasing the hole concentration, thereby reducing the contact resistance. When applied as a spacer doping strategy for a 3L-WSe2 p-MOSFET, WOx conversion significantly improves performance by lowering resistance in the access regions. The final section focuses on optimizing edge contacts, a potential contact scheme for 2D nanosheet devices, through two techniques: post-annealing and edge functionalization. Transfer characteristic measurements reveal that each method improves performance through distinct mechanisms. By combining both techniques with channel-length scaling, high-performance short-channel edge-contact p-FETs are successfully fabricated.

Contact engineering remains a critical challenge for practical applications of 2D TMDs and requires persistent research. The proposed strategies in this dissertation contribute to addressing key issues in specific applications and offer potential routes toward scalable production of 2D electronics.