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標題: 具高反射鏡面之金屬銅基板氮化鎵發光二極體之研製
Investigation of High-Brightness GaN Light-Emitting Diodes with Copper Substrate
作者: 嚴國瑋
Yen, Kuo-Wei
關鍵字: GaN;氮化鎵;LEDs;laser lift-off (LLO);electroplating;textured;發光二極體;雷射剝離技術;精密電鍍技術
出版社: 精密工程學系所
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論文主要利用高反射鏡面研製垂直導通型氮化鎵藍光LED,並探討元件特性及製程之可行性。論文進行方式使用雷射剝離技術來剝離藍寶石基板,搭配反射率達92 %的鎳/銀鏡面及精密電鍍技術,將剝離後的氮化鎵薄膜轉移至銅基板上,最後利用氫氧化鈉溶液粗化n型氮化鎵薄膜,製作p型在下的氮化鎵/鏡面/銅結構LED元件。將大面積( 1 mm×1 mm )垂直導通型之氮化鎵/鏡面/銅LED和傳統型氮化鎵/藍寶石基板結構作特性比較,其中順向偏壓在20 mA時分別為2.63 V及2.74 V,於電流350 mA時分別為3.88 V及3.94 V,在不同電流注入下,垂直型LED操作電壓較低是由於整面p型氮化鎵與金屬接觸和n型氮化鎵層之電流擴散所造成。在逆向偏壓-5 V時所量測到的漏電流分別為垂直型LED 90.2 nA及原始LED 47.8 nA,經由上述結果顯示此製程研究之可行性。
此外,在電流350 mA注入下氮化鎵/鏡面/銅結構經由粗化後的發光強度為傳統型藍寶石基板結構的4.3倍,之後隨著注入電流的增加至1 A,傳統型藍寶石基板之LED已先呈現飽和,而垂直導通型LED仍持續線性增加;注入350 mA電流後,垂直發光元件的電光轉換效率12%優於傳統型元件的7%,明顯地提高元件的效率;實驗亦發現元件在大電流(350 mA)注入後,具銅基板的發光元件介面溫度192oC相較於藍寶石基板元件的257oC降低了有65oC之多;顯示氮化鎵薄膜經由基板轉移至熱傳導係數極佳的金屬銅後,可以得到較佳的散熱機制,大電流操作下仍可維持良好的特性及穩定性。

In general, the structure of GaN light-emitting diode is commonly epitaxially grown on sapphire substrate. The large joule heat is generated from the active layer during high current injecting. That could degrade the performance of device because the low thermal conductivity of sapphire substrates. To solve this problem, GaN epilayer will be transferred to the copper substrate by electroplating. The copper substrate supplies high electrical conductivity and thermal conductivity.
In this study, a vertical conductive type structure for GaN/mirror/Cu LED combined with laser lift-off (LLO), Ni/Ag mirror with high reflectivity (about 92%), and electroplating technique are demonstrated. The Ni/Ag was deposited on the p-GaN layer and then electroplated by copper substrate. Following, using NaOH solution roughens the n type GaN cladding layer after LLO. The epitaxy structure is separated by LLO from the sapphire substrate to fabricate p-side down device. The forward voltage (@20 mA) of the GaN/mirror/Cu LEDs and conventional LEDs are 2.63 V and 2.74 V, respectively. The forward voltage (@350 mA) of the GaN/mirror/Cu LEDs and conventional LEDs are 3.88 V and 3.94 V, respectively. From these results, the GaN/mirror/Cu LEDs decrease the series resistance in a vertical conductive structure due to the large-area metal being ohmic to p-GaN and n-GaN providing well current spreading. The leakage currents (@-5 V) of GaN/mirror/Cu and conventional LEDs are 90.2 nA and 47.8 nA, respectively. The luminance intensity of GaN/mirror/Cu LEDs with textured surface is better than that of conventional LEDs. It is about 4.6 times. With injection current to 1 A, the light output power of GaN/mirror/Cu LEDs could be linearly increased. It is due to the copper providing a good conductivity and heat sink.
其他識別: U0005-2608200711523900
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