二維材料與元件之原子級解析：二硫化鉬電晶體金屬接觸之傳輸機制與雙面硫硒化鉬之缺陷調控電子結構

Abstract

隨著半導體技術逼近物理極限，二維材料因其優異的靜電控制能力被視為關鍵解方。然而，在實際應用上，「金屬接觸的微縮極限」與「新穎材料的缺陷電子特性」仍是兩大挑戰。本論文利用掃描穿隧顯微鏡與掃描穿隧能譜技術，針對上述議題進行了元件與材料的原子級探討。首先，針對元件層級的接觸電阻與傳輸機制，本研究開發了剖面臨場掃描穿隧顯微鏡技術 (STM/STS)。我們成功在超高真空環境下，對運作中的鉍接觸單層二硫化鉬電晶體進行量測，首次直接觀測到載子由金屬注入二維通道的距離變化，並精確量測出其特徵傳輸長度僅約 2.0 nm。此結果證實了二維材料搭配鉍接觸具有符合未來 1 nm 製程節點需求的微縮潛力。此外，針對材料層級的本質特性，本研究探討了具備內建電場的新穎 Janus MoSSe 單層材料。利用 STM/STS，我們首次解析了其複雜的缺陷電子結構。實驗發現，合成過程中的殘留硫摻雜會在價帶附近產生非均勻分布的淺層能隙態。我們進一步分析，鑑定出兩類本徵電荷缺陷：一類作為導電電荷陷阱，會顯著縮減局部能隙；而另一類則作為絕緣散射中心，具有較低的態密度特徵。本論文結合了創新的量測技術與微觀物理分析，探討原子級特徵如何影響二維材料與元件的巨觀表現，為下世代電子材料與元件的設計揭示了關鍵的研究方向。 本研究強調了單層硫硒化鉬的電子結構對奈米尺度組成和結構變化的高度敏感性，並展示了掃描穿隧式顯微鏡和掃描穿隧式光譜在原子尺度解析這些效應中的應用潛力。這些發現為理解二維詹努斯過渡金屬硫族化合物及其在電子學和光電子學中的潛在應用提供了重要的貢獻。

As semiconductor technology approaches its physical limits, two-dimensional (2D) materials are viewed as a key solution due to their superior electrostatic control capabilities. However, in practical applications, the "scaling limits of metal contacts" and the "defect electronic properties of novel materials" remain two major challenges. This dissertation utilizes Scanning Tunneling Microscopy (STM) and Scanning Tunneling Spectroscopy (STS) to conduct an atomic-scale investigation into both "devices" and "materials" regarding these issues. First, we addressed contact resistance and investigate transport behaviors at the device level. This study developed an Operando Cross-Sectional Scanning Tunneling Microscopy (Operando XSTM) technique. We successfully measured an operating bismuth (Bi)-contacted monolayer molybdenum disulfide (MoS2) transistor in an ultra-high vacuum environment. For the first time, we directly observed the carrier injection from the metal into the 2D channel and precisely measured the characteristic transfer length (LT) to be only approximately 2.0 nm. This result confirms the potential of 2D materials combined with Bi contacts to meet the scaling requirements of future 1 nm technology nodes. Furthermore, regarding the intrinsic properties at the material level, this research explored novel monolayer Janus MoSSe materials possessing an intrinsic electric field. Using STM/STS, we unraveled their complex defect electronic structure for the first time. Experiments revealed that residual sulfur dopants from the synthesis process generate non-uniformly distributed shallow in-gap states near the valence band. Further analysis identified two types of native charge defects: Type A (selenium vacancies) act as conductive charge traps that significantly reduce the local bandgap, while Type B (structural disorder) functions as insulating scattering centers with lower density of states features. Combining innovative measurement techniques with microscopic physical analysis, this dissertation investigates how atomic-scale features influence the macroscopic performance of 2D materials and devices, revealing key research directions for the design of next-generation electronic materials and devices. This study highlights the high sensitivity of the electronic structure of monolayer MoSSe to nanoscale compositional and structural variations, demonstrating the potential of STM and STS in resolving these effects at the atomic scale. These findings provide significant contributions to understanding 2D Janus transition metal dichalcogenides and their potential applications in electronics and optoelectronics.