二維P型半導體: 單層二硒化鎢材料合成與場效電晶體元件

Abstract

本研究主要分為兩部分，首先，我們專注於二硒化鎢(WSe2)薄膜的製備；其次，我們著手於二硒化鎢場效電晶體的製作。本研究成功於實驗室建置化學氣相沉積系統，我們成功合成出高品質的單層二硒化鎢薄膜。透過製程條件優化，包括製程溫度、載流氣體濃度、前驅物濃度以及持溫時間的調變，成功合成高均勻性與高品質的單層二硒化鎢薄膜。 材料特性的分析包括二次諧波生成 (SHG) 測試、拉曼光譜以及光致發光 (PL)譜圖。SHG結果顯示了薄膜的均勻性，而拉曼和PL譜圖的峰值位置與文獻報導相吻合，顯示了良好的材料特性。特別是PL波長為753 nm，對應到能隙為1.64 eV，證明了其直接能隙的特性，進一步透過X射線光電子能譜 (XPS) 分析，我們定量分析了W和Se元素的比例約為1 : 2，說明了材料的化學組成和薄膜的品質。 在元件製作方面，我們首先製備了長通道二硒化鎢電晶體。長通道元件的性能主要由通道材料決定，從而使我們能更準確地萃取場效遷移率。測量結果顯示，場效遷移率 μ_FE 達到33.3 cm²/V·s，這表明我們的二硒化鎢薄膜具有良好的半導體電特性。接著，我們製作了短通道元件，旨在更精確地提取半導體材料與金屬接面之間的接觸電阻。特別是在摻雜了MoOx層之後，元件的整體電性有了顯著的提升，Ion, max達到76.8 µm/µm，遷移率從8.35 cm²/V·s提升至27.5 cm²/V·s。最後利用傳輸線模型，我們成功萃取出接觸電阻約為5.65 kΩ。

This study is divided into two main parts: firstly, the preparation of tungsten diselenide (WSe2) thin films; and secondly, the fabrication of WSe2 field-effect transistors. In this research, we successfully established a chemical vapor deposition system in our laboratory and synthesized high-quality monolayer WSe2 films. Through the optimization of process conditions, including process temperature, carrier gas concentration, precursor concentration, and holding time, we were able to synthesize uniformly high-quality monolayer WSe2 films. The material characterization involved second harmonic generation (SHG) testing, Raman spectroscopy, and photoluminescence (PL) spectroscopy. The SHG results confirmed the uniformity of the films, while the peak positions in Raman and PL spectra matched well with those reported in the literature, indicating good material characteristics. Notably, the PL wavelength was 753 nm, corresponding to a bandgap of 1.64 eV, demonstrating its direct bandgap nature. Further, X-ray photoelectron spectroscopy (XPS) analysis quantitatively confirmed the W to Se elemental ratio of approximately 1:2, elucidating the chemical composition and quality of the films. In terms of device fabrication, we initially prepared long-channel WSe2 transistors. The performance of long-channel devices is primarily determined by the channel material, allowing us to extract the field-effect mobility more accurately. The measured field-effect mobility, μ_FE reached 33.3 cm²/V·s, indicating that our WSe2 films possess excellent semiconductor electrical characteristics. Subsequently, we fabricated short-channel devices to more precisely extract the contact resistance between the semiconductor material and the metal contacts. Notably, after doping with a MoOx layer, there was a significant enhancement in the overall electrical performance of the devices, with Ion, max reaching 76.8 µm/µm and mobility increasing from 8.35 cm²/V·s to 27.5 cm²/V·s. Finally, using the transfer length method, we successfully extracted a contact resistance of approximately 5.65 kΩ.