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研究生： 劉文獻
Wen-Hsien Liu
論文名稱： 提升P型Al0.5Ga0.5N歐姆接觸電極的導電性及反射率
Enhancing Conductance and Reflectivity of the Ohmic Contact to P-type Al0.5Ga0.5N
指導教授： 賴昆佑
Kun-Yu Lai
口試委員:
學位類別： 碩士
Master
系所名稱： 理學院 - 光電科學與工程學系
Department of Optics and Photonics
論文出版年： 2018
畢業學年度： 106
語文別： 中文
論文頁數： 57
中文關鍵詞： P 型氮化物
相關次數： 點閱：7  下載：0 
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    • P型氮化物半導體大多以鎳金(Ni/Au)作為歐姆接觸電極。對覆晶型(Flip-Chip)深紫外(deep utralviolet, DUV, 波長 ≤ 290 nm) LED來說，金在DUV波段的反射率不到30%，嚴重犧牲元件的光萃取效率。為了解決此問題，我們在DUV LED的P型電極上需克服兩大難題：(1) 提升金屬電極在DUV波段的反射率；(2)降低P型氮化鋁鎵（Al0.5Ga0.5N）表面的接觸電阻。
    在本研究中，我們以Ni/Al/Ti/Au取代Ni/Au。我們利用高真空電子束暨熱阻式蒸鍍系統 (E-gun/Thermal)，在P型Al0.5Ga0.5N磊晶層上蒸鍍Ni/Al/Ti/Au，再分析退火溫度對Ni/Al/Ti/Au接觸電阻的影響。我們發現，550℃的退火溫度可將接觸電阻及片電阻分別從2.81x101 ohm-cm2及9.41x108 ohm/sq，降低至3.05x10-2 ohm-cm2及8.79x105 ohm/sq。在反射率方面，Ni/Al/Ti/Au在280 nm的反射率可達57%，遠高於Ni/Au的24%。雖然Ni/Al/Ti/Au的導電度有待改進，但由於Al的高UV反射率，可以補償其在電性上的損失。未來，我們將持續優化Ni/Al/Ti/Au的製程條件，希望能有效提升DUV LED的發光效率。

    Deep ultraviolet (DUV) LEDs traditionally employ Ni/Au as the ohmic contact to p-type AlGaN. However, for flip-chip devices, the reflectivity of gold at DUV wavelengths is below 30%, severely sacrificing the light extraction efficiency of DUV LEDs. To address the issues, there are two challenges to overcome with the p-type ohmic contact: (1) Increasing reflectivity in the DUV regime; (2) Decreasing the contact resistance on p-type Al0.5Ga0.5N.
    In this study, Ni/Au is replaced with Ni/Al/Ti/Au as the ohmic contact to p-type Al0.5Ga0.5N. The Al-based alloy was deposited by a high-vacuum electron-beam/thermal evaporation. The ohmic contact structure is then annealed at varied temperatures, with the attempt to reduce contact/sheet resistance. It is found that the annealing at 550 °C effectively reduces the specific contact resistance and the sheet resistance from 2.81x101 ohm-cm2 and 9.418x108 ohm/sq to 3.057x10-2 ohm-cm2 and 8.791x105 ohm/sq, respectively. For optical characterization, the reflectance of Ni/Al/Ti/Au at 280 nm reaches 57 %, significantly higher than that (24%) attained with Ni/Au. Although the conductivity of Ni/Al/Ti/Au on p-type Al0.5Ga0.5N remains to be improved, the high UV reflectivity is expected to compensate the loss in electrical performance. In the future, the fabrication of Ni/Al/Ti/Au will be optimized to enhance the external quantum efficiency of DUV LEDs.

    論文摘要................................................................................................................Ⅰ Abstract.................................................................................................................Ⅱ 致謝.....................................................................................................................Ⅲ 目錄.....................................................................................................................Ⅳ 圖目錄.................................................................................................................Ⅵ 表目錄..............................................................................................................Ⅷ 第一章 緒論 1-1前言……………………………………………………………………….1 1-2鋁電極應用深紫外光波長LED的優勢…………………...……….…...3 1-3研究動機………………………………………………………………….8 1-4論文架構………………………………………………………………...11 第二章 實驗原理、方法與儀器 2-1製程步驟………………………………………………………………...12 2-2 Transfer Length Method量測原理……………………………………...19 2-3紫外線/可見光分光光譜儀檢測………………………………………..21 2-4霍爾量測原理…………………………………………………………...23 第三章 結果與討論 3-1金屬電極對電阻值的影響……………………………………………...26 3-2反射率在入射光280nm波長的比較…….……….…….….………..….34 3-3利用退火降低接觸電阻與片電阻……………………………………...36 第四章 結論與未來展望 4-1結論……………………………………………………………………...42 4-2未來展望………………………………………………………………...43 參考文獻……………………………………………………………………….44

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