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標題: 深紫外光發光二極體P型電極之優化設計與提升光輸出功率之研究
Improvements of P-Electrode Design and Optical Output Power in Deep-Ultraviolet AlGaN LEDs
作者: 鄭智遠
Jhih-Yuan Jheng
關鍵字: 深紫外光發光二極體;P型電極的結構設計;歐姆接觸;外部量子效率;deep-ultraviolet light-emitting diodes;p-side electrode design;ohmic contact;external quantum efficiency
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本實驗利用電子槍真空蒸鍍機在試片表面沉積厚度為10/5 nm的鎳/金電極,作為深紫外光發光二極體的P型電極,並藉由不同P型電極結構設計以改善深紫外光發光二極體的光電特性。由實驗結果得知,鎳/金電極厚度、退火溫度與退火時間的選擇對於鎳/金電極與p+GaN歐姆接觸的形成極為重要;鎳/金電極厚度的比例,退火溫度及時間也都會影響其特徵電阻值。本研究的最佳鎳/金電極厚度及退火參數為:鎳/金=10/5 nm、大氣氛圍下500 C退火10分鐘,在此製程條件下試片的特徵電阻值為:2.32×10-6 Ω-cm2。
本實驗設計四種不同P型電極結構的深紫外光發光二極體(3指狀電極、6指狀電極、9指狀電極以及12指狀電極之發光二極體),並且與傳統型之發光二極體做比較,最後再進一步製作9及12指狀電極之覆晶式發光二極體進行元件特性探討。因深紫外光發光二極體的歐姆接層(p+GaN)會吸收280 nm波長的光,此電極結構設計的目的即為增加電流擴散能力及光輸出功率。由實驗結果得知,9 指狀電極之發光二極體的電流擴散能力及光輸出功率較佳。在注入電流20 mA下,其光輸出功率及外部量子效率較傳統型之發光二極體,分別提升約150%、200 %;當注入電流為350 mA時,其光輸出功率及外部量子效率較傳統型之發光二極體,則分別提升約172 %、198 %。將9指狀電極之發光二極體製作成覆晶式後,在注入電流20 mA下,覆晶後之光輸出功率較覆晶前提升139%;在光電轉換效率及外部量子效率方面方面,分別較覆晶前提升約173 %、182 % ;當注入電流為350 mA時,覆晶後之光輸出功率較覆晶前提約92%;在光電轉換效率及外部量子效率方面,則分別較覆晶前提升約71%、79 %。由本研究結果得知,可藉由不同P型電極設計來提升深紫外光發光二極體的電流擴散能力及光輸出功率。

In this thesis, the Ni/Au (10/5 nm) films were grown on p+GaN layer by electron beam evaporation. The Ni/Au films were employed as a p-side electrode for the deep-ultraviolet light-emitting diodes (DUV-LEDs). Via the structural design of the p-side electrode, the optoelectronic performances of DUV-LEDs can be improved.
Based on the experimental results, it can be found that the formation of an ohmic contact between Ni/Au and p+GaN are mainly affected by the thickness of Ni/Au and the parameters of annealing process for this p-side electrode (such as annealing temperature and annealing time). In this study, the most suitable thickness of Ni/Au electrode is 10/5 nm. Additionally, after annealing in air atmosphere at 500 C for 10 min, the ohmic contact characteristic between Ni/Au and p+GaN can be optimized, where its lowest specific contact resistivity reaches to 2.32×10-6 Ω-cm2.
DUV-LEDs with four kinds of p-side electrode design (denoted as 3 fingers-LED, 6 fingers-LED, 9 fingers-LED, and 12 fingers-LED) were fabricated, and the conventional-LED was prepared as a contrasted sample. Besides, the 9 fingers-LED and 12 fingers-LED samples were further fabricated to flip-chip device. Because the emission light with a wavelength of 280 nm would be absorbed by the p+GaN layer, the purpose of this study is to improve the current spreading ability and the light output power of the LEDs through the p-side electrode design. The experimental results indicate that the 9 fingers-LED possessed better optoelectronic performances than those of the LEDs. At injection currents of 20 and 350 mA, the 9 fingers-LED exhibited 154% and 172% enhancements in the output power in comparison to those of conventional-LED, while the improvements in the external quantum efficiency (EQE) were 200% and 198%, respectively. After fabricating the flip chip device, the optoelectronic performances were further improved. At an injection current of 20 mA, the flip chip device possessed 139%, 173%, and 182% improvements in the output power, wall-plug efficiency, and EQE, respectively, as compared with those of 9 fingers-LED. Further increasing the injection current to 350 mA, the flip chip sample can achieve 92%, 71%, and 79% enhancements in the output power, wall-plug efficiency, and EQE, respectively, in comparison to those of 9 fingers-LED. These results clearly indicate that the p-side electrode design is useful for improving the optoelectronic performances of DUV-LEDs.
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