利用空氣洞結構與氮化鋁(銦)鎵薄插入層加以改善藍光與紫外光發光二極體之特性

Performance improvement of blue and UV LEDs by using an air-void structure and inserting a thin Al(In)GaN interlayer

劉嘉哲(Jia-Zhe Liu)

指導教授 ： 吳孟奇

國立清華大學/電機資訊學院/電子工程研究所/博士(2015年)

摘要

本論文主要分為兩個研究主題。第一個主題主要是在未圖案化的平面基板上(FSS)和圖案化基板(PSS)上，埋入具有50%高比率空氣洞結構來加以改善藍光、400-nm與380-nm紫外光發光二極體(light-emitting diodes, LED)的相關特性。從SEM與TEM結果觀察，能明顯看到無空氣洞之區域，差排缺陷 (threading dislocations,TDs)會往上延伸。而有空氣洞之區域，差排缺陷會被阻擋住，故此結構能有效降低差排缺陷密度。XRD繞射峰也同樣顯示，埋入空氣洞後，有較低之(002)與(102) 半高寬值，證明了加入空氣洞結構後，能有效改善磊晶材料品質，此結果與SEM與TEM觀察相符。同時，氮化鎵(n=2.38)與空氣洞(n=1)介面之間也會有較高之光反射，進而提升光取出效率。最後，在未圖案化的平面基板上(FSS)和圖案化基板(PSS)上埋入具有50%高比率空氣洞結構後，與傳統圖案化基板(C-PSS)的LED相比，光輸出功率與外部量子效率能有效提升。值得注意地，在可靠度測試方面，當400-nm與380-nm紫外光發光二極體具有空氣洞結構時，與沒有空氣洞結構的發光二極體相比，能明顯改善長時間所造成的光功率衰退與漏電流增加。此技術能有效的商業化並且能供選擇性的取代傳統圖案化基板LED。
在第二個研究主題方面，主要是在討論多重量子井(MQW)中的位障層(Barrier)與發光層(Well)之間加入薄的氮化鋁(銦)鎵埋入層(A(In)GaN interlayer)，並且具有較大能隙的。經由插入漸變的鋁含量(由低至高)的氮化鋁鎵(AlGaN)與氮化鋁(銦)鎵(AlInGaN)埋入層後，與無插入層結構相比，光輸出功率能有效分別提升約70 % 與105%。此重要的效率改善主要是歸功於電子侷限與電洞注入的增加，進而導致在多重量子井中獲得更均勻的分佈。另外，光激發螢光(Photoluminescence, PL)與原子力顯微鏡 (Atomic force microscope, AFM)分析顯示，加入漸變組成的氮化鋁銦鎵(Al(In)GaN)埋入層後，能改善多重量子井的磊晶品質。

關鍵字

發光二極體 ； 空氣洞 ； 圖案化藍寶石基板 ； 氮化鋁銦鎵插入層 ； 多重量子井

並列摘要

This research contains two major topics. Firstly, we analyze the efficiency enhancement of blue light-emitting diodes (LEDs), 400-nm and 380-nm ultraviolet (UV) LEDs by incorporating an air-hole layer within the epitaxial structure. As compared to the conventional patterned sapphire substrate (C-PSS) LEDs and flat sapphire substrate (FSS) LEDs with air-hole, the fabricated patterned sapphire substrate (PSS) LEDs with air-hole exhibit the lowest full width at half maximum (FWHM) of (002) and (102) diffraction peaks, the better light output power, and the highest external quantum efficiency. Remarkable performance improvement in the PSS LED with air-hole is attributed to the better epitaxial quality with threading dislocations terminated by the air-hole structure and the higher scattering at interface between GaN and air-void. In terms of the reliability test after 72 hrs, the decay of the light output power would be outstandingly improved for the 400-nm and 380-nm UV-LEDs. It is well proposed that this methodology provides a promising alternative to C-PSS LEDs.
Secondly, the performance improvement of 380-nm InGaN/AlGaN UV-LEDs are investigated by incorporating an undoped Al(In)GaN thin interlayer between the InGaN well and AlGaN barrier in multi-quantum-well (MQW) active region. By inserting the graded-composition AlGaN and AlInGaN thin interlayers, the light output powers of UV-LEDs are significantly increased by 70% and 105% at 20 mA, respectively, as compared to the LED without the interlayer. Remarkable efficiency enhancement in the UV-LEDs with graded-composition AlGaN and AlInGaN interlayers is mainly attributed to the further improvement of the electron confinement and hole injection with more uniform distribution in the MQW active region. Besides, photoluminescence (PL) and atomic force microscope (AFM) analyses indicate that the MQW quality can be enhanced by incorporating a graded-composition AlInGaN thin interlayer in the MQW active region of UV-LEDs.

並列關鍵字

Light-emitting diode (LED), ； air-hole ； patterned sapphire substrate (PSS) ； Al(In)GaN interlayer ； multi-quantum-well (MQW)

參考文獻

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