Fabrication of N-Electrodes for Deep-Ultraviolet AlGaN LEDs and its Recovery Studies after Plasma Damage

本研究利用氨水水霧退火法修復因ICP-RIE電漿蝕刻造成損傷的n-Al0.58Ga0.42N表面。藉由改變氨水水霧退火溫度與氨水濃度，探討經氨水水霧退火法修復後的金屬/n-Al0.58Ga0.42N接面特性與其應用於深紫外光發光二極體的元件特性。 透過分析實驗結果得知，沒有經氨水水霧退火法修復之試片，金屬與n-Al0.58Ga0.42N之間雖然可形成歐姆接觸，其特徵電阻為5.28×10-3 Ω∙cm2。但在經過氨水水霧退火法修復後(退火溫度900C、氨水濃度3.6M、退火時間20分鐘)n-Al0.58Ga0.42N可以與金屬形成良好的歐姆接觸，並且使特徵電阻大幅降低至6.18×10-4 Ω∙cm2。根據X光射線光電子能譜儀的量測結果顯示，當經氨水水霧退火修復後之n-Al0.58Ga0.42N表面鋁與鎵的特徵峰都往高束縛能方向偏移，此現象經分析是與氧摻雜有關；而紫外光光電子能譜儀的量測結果分析得到的能帶來看，經氨水水霧退火法修復後因為六價的氧摻雜取代了原本五價的氮原子的位置，使自由電子濃度增加，造成費米能階往導電帶靠近，因此n-Al0.58Ga0.42N更容易與金屬形成歐姆接觸使電性大幅提升。 為了確認氨水水霧退火法修復n-Al0.58Ga0.42N對於280 nm 深紫外光發光二極體的影響，將最佳化之氨水水霧退火條件應用於元件上。與未經處理元件相比，其啟動電壓在350 mA的電流注入下由7.212 V下降至6.926 V，下降比例約4.1%，在20mA電流注入下EQE從0.27%增加至0.61%；研究結果顯示氨水水霧退火法可以有效降低金屬/n-Al0.58Ga0.42N的接面阻抗，使元件電性獲得改善。In this thesis, an ammonium hydroxide (NH4OH) mist annealing treatment was used to repair plasma-etched damage n-Al0.58Ga0.42N surface. The effects of annealing temperature and ammonium hydroxide solution concentration on the characteristics of metal/n-Al0.5Ga0.5N and DUV-LEDs optoelectronic performance were investigated in detail. According to the experiment results, the specific contact resistance of the n-Al0.58Ga0.42N without treatment is 5.28×10-3 Ω∙cm2. As the plasma-etched sample treated with NH4OH mist anneal at 900C for 20 minutes with ammonium hydroxide concentration 3.6M, the contact resistance was significantly decrease to 6.18×10-4 Ω∙cm2. From XPS measurement results, the Al 2p and Ga 3d core peaks of n-Al0.5Ga0.5N both shift to higher binding energy after treatment, implying the Al-O and the Ga-O bond formation cause by oxygen doping in n-Al0.5Ga0.5N；From UPS measurement results, the fermi level of the treated sample was found closer to conduction band. This can be explained by the increment of free electron concentration by Oxygen doping. Under the injection current of 350 mA, the forward voltage of DUV-LEDs with NH4OH mist annealing treatment is 6.926 V which is 4.1% smaller than that of the without treatment one (7.212 V). Besides, the EQE of treatment sample gradually increase to 0.61% under the injection current of 20 mA. The experiment results strongly evidence that the specific contact resistance can be significantly reduction after NH4OH mist annealing treatment on plasma-damaged n-AlGaN. This treatment will benefit on the electrical and optoelectrical properties of DUV-LEDs.誌謝 i 摘要 ii Abstract iii 目錄 v 圖目錄 viii 表目錄 xi 第一章 緒論 1 1-1 前言 1 1-2 研究動機 3 1-3 論文架構 5 第二章 理論基礎與文獻回顧 6 2-1 氮化鋁鎵材料介紹與應用 6 2-2 光電特性 9 2-3 金屬與半導體接觸之原理 11 2-4 蕭特基能障原理 11 2-5 歐姆接觸原理 14 2-6 傳輸線模型原理 18 2-7 ｎ型氮化鋁鎵歐姆接觸與表面電漿損傷介紹文獻回顧 19 第三章 實驗方法與儀器介紹 23 3-1 前言 23 3-2 金屬厚度優化 23 3-2-1 試片準備 23 3-2-2 CTLM量測歐姆接觸於280 nm DUV-LEDs經ICP-RIE蝕刻至n-Al0.58GaN0.42試片 24 3-3 載流氣體與溶液對電性影響 25 3-4 氨水水霧退火溫度與氨水濃度對修復電性程度的影響 25 3-4-1 比較爐管退火溫度對n-Al0.58Ga0.42N電性修復的影響程度 25 3-4-2 比較氨水濃度對n-Al0.58GaN0.42 電性修復的影響程度 25 3-5元件製備 26 3-5-1 深紫外光氮化鋁鎵試片之磊晶結構 26 3-5-2 定義平台 27 3-5-3 氨水水霧爐管退火修復ICP-RIE蝕刻損傷之n-Al0.58Ga0.42N 28 3-5-4 電極製作 28 3-5-5 元件切割 28 3-6 儀器介紹 30 3-6-1 電子束蒸鍍系統(E-beam Evaporator) 30 3-6-2 化學分析電子能譜儀(Electron Spectroscopy for Chemical Analysys) 30 3-6-3 輝光放電分光儀(Glow Discharge Spectrometer) 33 第四章 結果與討論 35 4-1 前言 35 4-2 金屬電極優化 35 4-3 載流氣體與溶液對電性影響 38 4-3-1 氨水水霧對修復n-Al0.58Ga0.42N電性的影響 38 4-3-2 GDS 探討退火對n-Al0.58Ga0.42N膜內元素縱深影響 42 4-4 探討退火溫度對氨水水霧修復n-Al0.58Ga0.42N損傷的影響 49 4-5 氨水濃度對蝕刻損傷n-Al0.58Ga0.42N修復程度的影響 51 4-6 探討氮氣攜帶氨水水霧退火修復n-Al0.58Ga0.42N原因 54 4-7 氨水水霧修復對元件影響 57 第五章 結論與未來展望 60 參考文獻 62 附件一 6