Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/10312
標題: 具異質高取光結構之氮化物發光元件
Nitride-based optoelectronics with high light extracted heterostructures
作者: Tsai, Peng-Han
蔡鵬翰
關鍵字: LiAl LDH
鋰鋁層狀雙氫氧化物
AZO
air voids
氧化鋅鋁
空孔
出版社: 材料科學與工程學系所
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摘要: 本論文中我們在氮化銦鎵發光二極體元件表面加入異質粗化結構,以及埋入微米柱狀結構於磊晶層中,探討微結構對於電性及磊晶過程的影響,並探討其外部量子效率的提升情形。 實驗中的第一部分,於圖案化藍寶石基板成長氮化銦鎵發光二極體結構,於磊晶試片表面分別鍍上厚與薄的Li/Al LDH(layered double hydroxide)結構,發現表面平坦的標準片其螢光光譜中干涉條紋十分明顯,而經片狀結構粗化過的試片其干涉條紋並不明顯,此外厚的Li/Al LDH結構其粗化效果較為明顯,但成長於發光元件上的附著性較不佳。我們選用薄的Li/Al LDH成長於元件表面,從光電特性的量測上可發現具LDH-LED與ST-LED於20mA下操作電壓同為3.1V,ST-LED與LDH-LED在給予反向偏壓-5V時其反向電流分別為2.28×10-8A與1.01×10-10A,在20mA正電流注入下其發光強度也有31.2%的提升,這表示此結構除了能提升光取出效率外,其包覆於元件平台側壁的Li/Al材料具有絕緣性質能夠阻絕電流漏電的途徑。此外在電激發螢光發散角量測也發現ST-LED與LDH-LED的發散角分別為141.4˚和132.9˚,此結果表示LDH-LED具有光集中效果。另外在太陽能電池特性量測上,LDH-LED在光電轉換效率峰值370nm處,相較於ST-LED有20.9%的提升。 實驗中的第二部分,於藍寶石基板上以再磊晶成長的方式成長發光二極體,於磊晶結構中埋入5μm的AZO微米柱,觀察埋入結構對於磊晶過程的影響,並探討其對於元件光電特性的影響。首先觀察光學顯微鏡圖,發現經高溫磊晶過程後的AZO微米柱縮聚成空心環狀結構,以場發射式顯微鏡觀察其剖面圖發現再磊晶界面處具有許多奈米空孔形成。從光電特性量測上得知APER-LED(AZO pillar -embedded regrowth)與ST-LED於20mA下操作電壓同為3.16V,表示此埋入式異質結構並未造成元件電性上的影響。在20mA電流注入下APER-LED的發光強度提升了41.2%,這是因為磊晶時所產生的空孔能夠提供量子井中的螢光在背向的全反射,使得光集中反射至元件正向。ST-LED和APER-LED其所對應的發散角度分別為140.6˚和134˚,顯示空孔的反射有助於光集中的現象。
In this thesis, the surface of the InGaN-based light-emitting diodes (LEDs) were roughened by Li/Al LDH hetero-materials, and we embedded AZO micro-pillar structures in epitaxial layers as well. The electrical properties and the epitaxial quality of the devices were analyzed in experiments, moreover, investigating the enhanced ratio of the external quantum efficiency (EQE) of LEDs. The first part of the experiment, epitaxial specimens with InGaN/GaN multi-quantum wells were grown on the patterned sapphire substrates, and then it were coated with thick and thin Li/Al LDH films.We found that there were serious Febry-Perot interference fringes in PL spectrum in the specimen without Li/Al LDH structures, but smooth PL spectrum in the specimen with Li/Al LDH platelet structures on the surface instead. Since it was harder to grow the thick Li/Al LDH films on the LEDs, we chose the thinner one for the optical and electrical mearsurements. The operating voltages of ST-LED and LDH-LED were almost the same at the value of 3.1V. At -5V reverse bias voltage, the reverse leakage currents were measured as the values of -2.28×10-8A and -1.01×10-10A for the LED structures without and with the Li/Al LDH films, respectively. The LED surface was covered with the Li/Al LDH films acted as a passivation layer without damaging the ITO TCL layer. At 20mA operating current, the light output power of the LDH-LED structure had a 31.2% enhancement compared to the ST-LED structure. The divergence angles were calculated 140.6˚ and 134˚ for ST-LED and LDH-LED, representing the LDH structures could concentrate the light out of the quantum wells. Besides, the peak wavelength of conversion efficiency at 370nm was enhanced by 20.9% compared to the ST-LED in the solar cell measurement. The second part of the experiment, the epitaxy of light emitting diode on sapphire substrate was embedded with 5μm AZO micro-pillars in epitaxial layers. We tried to find out the effect of the embedded structure and investigate the optical and electrical properties of the device. From the optical microscope, the AZO micro-pillars condensed into a hollow ring structures after the high temperature regrowth process, and FE-SEM figures showed the cross-section images of the regrowth interface comprising many nano-voids. APER-LED and ST-LED had the same operating voltage of 3.16V at 20mA, standing for embedded heterostructures didn't cause the deterioration in the epitaxy quality. The light output power of APER-LED at 20mA had a 41.2% enhancement compared with ST-LED, and it was attributed to the light reflection in the interface of GaN and air voids. The divergence angles of ST-LED and APER-LED were calculated 140.6° and 134 °, respectively. From the smaller divergence angle, we concluded the reflection of air voids could contribute to the light concentration.
URI: http://hdl.handle.net/11455/10312
其他識別: U0005-2606201210084400
文章連結: http://www.airitilibrary.com/Publication/alDetailedMesh1?DocID=U0005-2606201210084400
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