在本研究中二硒化鎢是一種p型半導體，它擁有良好的光電特性，例如載子遷移率和光響應度。不過在半導體的元件應用當中，需要有n型材料與p型材料搭配。因此，本研究中我們透過氧電漿對二硒化鎢進行處理，因為材料表面形成鎢的氧化物，使材料從p型變為n型半導體。隨著電漿功率的增強，二硒化鎢的電荷中性點從65 V移動到-125 V；並分別利用X射線光電子能譜儀確認氧原子比例的增減和WOx (x≦3) 的鍵結方式。我們使用絕緣遮罩，只處理半邊的二硒化鎢，在單質材料上製作pn二極體；透過電流-電壓特性曲線，確認此pn二極體表現。接著將此二硒化鎢二極體應用到半波整流電路中，輸入電壓峰對峰值為6 V，工作頻率從1 Hz至500 Hz。最後的應用將二硒化鎢二極體製作為光二極體，以二硒化鎢吸光度較佳的405 nm雷射進行光感測器實驗，外加逆向偏壓為0.1 V；另外也製作未經電漿處理與整面電漿處理的二硒化鎢樣品作為光導體，進行光電流量測並比較三種樣品的光學特性。量測結果發現光二極體相較光導體樣品，其光電導率和歸一化光響應度上有顯著提升。因為光二極體設置在逆向偏壓下使空乏區變寬、內建電場增強的緣故，進而促進空乏區內光電流的產生。本研究經由電漿處理的方式，提供一個較低成本並有效製作二極體元件、提升光感測器表現的方法。

In this study, tungsten diselenide (WSe2) is a p-type semiconductor with outstanding electrical and optical properties such as carrier mobility and photoresponsivity. Nevertheless, in order to form p-n junctions, elementary “building blocks” of semiconductor electronic devices, n-type semiconductor is required. Thus, WSe2 was doped with oxygen plasma, transforming WSe2 from p-type to n-type configuration, which was due to the formation of WOx (x≦3) on the surface. As the power of plasma rising, the charge neautrality point of WSe2 shifted from 65 V to -125 V. After doping, Raman spectroscope was used to determine emerging vibration modes that originated from WSe2. According to X-ray photoelectron spectroscopy and X-ray diffraction measurement, binding of tungsten and oxygen atoms and shifting of 2θ were analyzed, respectively. In addition, homojunction p-n diode was constructed after oxygen plasma treatment with insulated mask which covered a half surface area of multilayer WSe2. Moreover, the performance of WSe2 p-n diode was verified by measuring current-voltage characteristic and applying the diode in half-wave rectifier circuit with Vpp = 6 V and input frequency from 1 Hz to 500 Hz. For further application, WSe2 p-n diode was fabricated as photodiode and demonstrated photocurrent properties in photoconductive mode with illumination of 405 nm laser and bias of 0.1 V. Pristine and oxygen plasma treated WSe2 were measured as well as photoconductors for comparison. Due to reverse bias increased the depletion region width, and electric field in depletion region was increased as well, which lead to the result of WSe2 photodiode performing higher normalized photoresponsivity over which of photoconductors. This study introduced an inexpensive and simple way to fabricate a WSe2 p-n diode and to enhance its electro-optical properties.

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