Interfacial Elemental Analysis of Slanted Edge- Contacted MoS2 Transistors Fabricated via Directional Etching with Multiple Metals

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题名:	Interfacial Elemental Analysis of Slanted Edge- Contacted MoS2 Transistors Fabricated via Directional Etching with Multiple Metals
作者:	林嘉俊;Lin, Chia-Chun
贡献者:	物理學系
关键词:	指向蝕刻;邊界電極;過渡金屬硫族化合物;元素分析;介面化學特性;directional etching;edge contact;transition metal dichalcogenides;elemental analysis;interfacial chemical property
日期:	2025-07-30
上传时间:	2025-10-17 11:56:49 (UTC+8)
出版者:	國立中央大學
摘要:	二維（2D）過渡金屬硫族化合物（TMDs），特別是二硫化鉬（MoS₂），因其可調控能隙、適中的載子遷移率以及機械柔性等獨特物理特性，在新一代奈米電子與光電裝置中展現出極大潛力。其中，以 MoS₂ 為通道材料的場效電晶體（FET）已被廣泛研究。然而，這類裝置的效能常受限於金屬與半導體間電極的品質不佳。傳統的表面電極方式在金屬與 MoS₂ 間存在能隙，進而產生高電極電阻、費米能階釘扎效應，以及無法有效調控蕭特基障礙，嚴重影響載子注入效率與開關特性。為了克服上述限制，邊緣電極（edge electrode）結構被提出並證明具備多項優勢。與傳統電極方式不同，邊緣電極直接與 MoS₂ 晶體的邊緣進行鍵結，有助於形成較強的化學鍵與軌域混成，提升電流注入效率。此外，此幾何結構也有助於縮短轉移長度、增進電場控制能力，並且適合應用於材料封裝技術，有效保護對環境敏感的2D 材料。近期研究指出，半金屬材料如鉍（Bi）、銻（Sb）與石墨，因其低費米能階附近態密度與高載子濃度，在 MoS₂ 邊緣電極中展現出優異表現。這些材料的層狀結構有利於形成乾淨、銳利的異質結界面。然而，即使在邊緣電極裝置中，電極介面的化學性質仍會顯著影響元件性能，特別是氧化物的生成。當 MoS₂ 邊緣經蝕刻後暴露於環境中，極易形成氧化鉬（MoOₓ），這些氧化物會形成穿隧障礙、陷阱態，並干擾能帶對齊，導致電極電阻增加。為了減緩這些影響，已發展多種介面工程方法，包括原質金屬沉積、真空退火、表面鈍化處理等。此外，利用氮化硼（hBN）等穩定的2D 材料進行封裝，也能有效防止製程後的氧化現象。進一步，利用如 X 射線光電子能譜（XPS）、掃描穿透式電子顯微鏡（STEM）與能量散射X 射線譜（EDS）等先進表徵技術，有助於深入了解電極界面在原子尺度的化學與電子結構。總結而言，對金屬－氧化層－半導體三者之間介面的精準調控，將是實現高性能、穩定且可擴展之 MoS₂ 邊緣電極電晶體的關鍵。;Two-dimensional (2D) transition metal dichalcogenides (TMDs), particularly molybdenum disulfide (MoS₂), have attracted significant interest for future nanoelectronic and optoelectronic applications owing to their unique physical properties, including tunable bandgaps, reasonable carrier mobilities, and mechanical flexibility. Among various device architectures, field-effect transistors (FETs) based on MoS₂ have shown great potential. However, the performance of these devices is often limited by inefficient electrical contacts, primarily due to the presence of a van der Waals (vdW) gap and poor orbital overlap between the metal and semiconductor in conventional top-contact configurations. These issues lead to large contact resistance, strong Fermi-level pinning, and limited control over Schottky barrier height, ultimately degrading carrier injection and switching behavior. To address these challenges, edge-contact geometries have emerged as a promising alternative, offering several inherent advantages. Unlike top contacts that interact with the basal plane of MoS₂, edge contacts form an interface at the exposed edges of the crystal, allowing for stronger chemical bonding and enhanced orbital hybridization. This geometry supports improved electrostatic control, reduced transfer length, and compatibility with encapsulation techniques—critical for protecting chemically sensitive materials and enabling device stability in ambient environments. Recent studies have demonstrated that semimetallic materials such as bismuth (Bi), antimony (Sb), and graphite are well-suited for edge contacts. Their unique electronic structures, characterized by low density of states near the Fermi level and high carrier concentrations, enable better energy alignment with MoS₂ and minimal Fermi-level pinning. Furthermore, their layered nature allows for clean, atomically sharp interfaces that are favorable for heterostructure assembly. Despite these advantages, the performance of edge-contacted devices remains highly sensitive to the interfacial chemistry, particularly the formation of oxide species during v fabrication or environmental exposure. Oxides such as MoOₓ can form at the etched MoS₂ edges, acting as tunneling barriers, introducing trap states, and disrupting charge transport. To mitigate these detrimental effects, various interface engineering strategies have been employed, including in-situ metal deposition, vacuum annealing, and surface passivation. Encapsulation using stable 2D materials like hexagonal boron nitride (hBN) has also proven effective in preventing post-fabrication oxidation. Advanced characterization techniques such as X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS) are essential tools for probing the interfacial structure and chemistry. Overall, precise control over the metal–oxide–semiconductor interface is crucial for realizing high-performance, reliable, and scalable 2D FETs with edge-contact architectures.
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