利用光電子能譜儀探討不同金屬與過渡金屬硫族化合物之接觸介面分析

Abstract

本研究探討了使用乾式轉移樣品製備的方法來研究過渡金屬硫族化合物與接觸金屬之間的介面分析。透過此方法可使用 X 射線光電子能譜儀和紫外光電子能譜儀直接測量過渡金屬硫族化合物與接觸金屬之間的功函數變化及能帶結構，進而深入理解它們的相互作用及其對元件性能的影響。 研究首先針對不同接觸金屬與單層二硫化鉬之間的接觸介面進行了分析。根據 X 射線光電子能譜儀和紫外光電子能譜儀的數據，觀察到三種主要的作用模式：接觸介面具有高金屬誘導能隙態導致費米能階釘札、較少的金屬誘導能隙態以及接觸介面摻雜。使用高功函數金屬如鉑、鈀、金和鎳作為接觸金屬時，經過數值計算，觀察到費米能階釘札現象，由於金屬誘導能隙態的產生，對元件性能造成不利影響。而使用了銻和鉍作為接觸金屬，並分別覆蓋金作為保護層，其結果顯示，使用銻作為接觸金屬可以顯著減少金屬誘導能隙態的形成概率，從而達到透過金屬功函數調變單層二硫化鉬介面處有效功函數之效果。鉍接觸金屬顯示了 N 型摻雜行為，部分鉍在暴露於大氣後氧化，接觸金屬中形成的氧化鉍具有約 3.75 電子伏特的功函數，進一步調控了接觸介面之功函數。這些發現表明，透過選擇適當的接觸金屬和摻雜策略，可以有效調控過渡金屬硫族化合物元件的電子性能。 接著，研究中亦探討不同接觸金屬與單層二硒化鎢之間的接觸介面。確認了高功函數金屬如鈀、鉑、金和鎳，使用於單層二硫化鉬與單層二硒化鎢做為接觸金屬，皆導致產生大量的金屬誘導能隙態，更進一步的造成極明顯的費米能階釘札結果。而使用銻作為半金屬接觸金屬時，其特性有助於減少金屬誘導能隙態的形成，然而由於單層二硒化鎢相比單層二硫化鉬具有較強的費米能階釘札效應，導致其接觸金屬作用後的有效功函數仍被釘札在單層二硒化鎢能隙中間。 最終，本研究提出了使用銻與鉑的異質結構層作為單層二硒化鎢場效電晶體的接觸金屬。通過調節銻的厚度，可以改變單層二硒化鎢通道的多數載子極性。 電性量測結果顯示，銻與鉑異質混合結構接觸金屬對單層二硒化鎢場效電晶體的轉移特性具有顯著影響，證實了銻的應用能有效減少對單層二硒化鎢的破壞，進而提高元件的整體功函數。 總述本研究，通過乾式轉移樣品製備方法，成功獲取了過渡金屬硫族化合物與金屬接觸介面之間的重要電子特性信息，為設計更高效能的過渡金屬硫族化合物元件提供了理論支持和實驗依據。這種方法為改善接觸金屬與過渡金屬硫族化合物的費米能階釘札問題提供了有效策略，對未來元件性能的提升具有重要意義。

This study explores the use of a dry transfer sample preparation method for interfacial analysis between transition metal chalcogenides and contact metals. This method allows for the direct measurement of work function changes and band structure between transition metal chalcogenides and contact metals using X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy, thereby gaining a deeper understanding of their interactions and their impact on device performance. The research initially analyzed the contact interfaces between various contact metals and monolayer molybdenum disulfide. Based on the data from X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy, three main interaction modes were observed: a high metal induced gap state leading to Fermi level pinning, fewer metal induced gap states, and contact interface doping. When using high work function metals such as platinum, palladium, gold, and nickel as contact metals, Fermi level pinning phenomena were observed through numerical calculations due to the creation of metallic-induced gap states, adversely affecting device performance. On the other hand, using antimony and bismuth as contact metals, with gold respectively serving as a protective layer, results showed that using antimony as a contact metal could significantly reduce metal induced gap states formation, thus achieving effective work function modulation at the monolayer molybdenum disulfide interface. Bismuth contact metal exhibited n-type doping behavior, with part of the bismuth oxidizing upon exposure to the atmosphere, forming bismuth oxide in the contact metal with a work function of about 3.75 electron volts, further modulating the interface work function. These findings indicate that by selecting appropriate contact metals and doping strategies, the electronic performance of transition metal chalcogenide components can be effectively controlled. Furthermore, the study also explored different contact metals with monolayer tungsten diselenide interfaces. It was confirmed that high work function metals such as palladium, platinum, gold, and nickel, used with monolayer molybdenum disulfide and monolayer tungsten diselenide as contact metals, all led to the creation of a significant number of metal induced gap states, further resulting in pronounced Fermi level pinning effects. While using antimony as a semimetal contact metal helped reduce the formation of metallic-induced gap states, the stronger Fermi level pinning effect of monolayer tungsten diselenide compared to monolayer molybdenum disulfide still pinned the effective work function after contact metal interaction to the middle of the monolayer tungsten diselenide gap. Ultimately, the study proposed using a heterostructure of antimony and platinum as contact metals for monolayer tungsten diselenide field-effect transistors. By adjusting the thickness of antimony, the majority carrier polarity of the monolayer tungsten diselenide channel could be changed. Electrical measurement results showed that the antimony and platinum heterostructure contact metals significantly affected the transfer characteristics of the monolayer tungsten diselenide field-effect transistors, confirming that the application of antimony could effectively reduce damage to monolayer tungsten diselenide, thereby improving the overall work function of the device. In summary, through the dry transfer sample preparation method, this study successfully obtained crucial electronic characteristic information between transition metal chalcogenides and metal contact interfaces, providing theoretical support and experimental basis for designing more efficient transition metal chalcogenide components. This method offers an effective strategy for improving the Fermi level pinning issues between contact metals and transition metal chalcogenides, which holds significant implications for future enhancement of device performance.