本論文旨在針對利用雷射剝離與電鍍鎳金屬基板技術所製作之氮化鎵系列垂直結構發光二極體(GaN-VLEDs)以及磷化鋁鎵銦系列發光二極體(AlGaInP-LEDs)進行光輸出功率與發光效率之改善。針對GaN-VLEDs與傳統水平藍寶石基板發光二極體(Regular LEDs)結構，GaN-VLEDs因導電基板較厚且較易電流擴散之n-GaN在結構上方之故，擁有散熱佳、短電流傳導路徑、較少的電流擁擠效應(Current crowding effect)與單電極而發光面積大等優點。然而，為要早日達到VLEDs可應用於一般照明，VLEDs仍需持續改善增進其光析出效率。而以四元AlGaInP元件而言，由於磊晶技術的突飛猛進，使得紅光元件內部量子效率已達90%以上，但是因為其GaAs為吸光基板，而且散熱不佳，若要應用在大面積、高功率、高效率的照明上，恐會有所限制。面對以上的問題與挑戰，本論文提出了改善GaN-VLEDs與AlGaInP-LEDs的發光效率之新穎製程。
首先，為能更加改善本實驗室先前所製備之VLEDs光析出效率，本研究提出一種利用聚苯乙烯奈米小球形成之光罩搭配乾式蝕刻與濺鍍沉積製程，製備出GaN奈米柱與銦鋅氧化物(Indium Zinc Oxide, IZO)奈米井陣列以提昇VLEDs光析出之方法。相較於表面只有KOH粗化之VLEDs，此方法製備之VLEDs光輸出功率與順向電壓分別在操作電流350 mA下增加97.5%與降低0.14伏特。
其次，為了能夠於n-GaN表面上均勻並大面積的製作出奈米結構，本團隊發表了利用水熱法(HTG)成長氧化鋅奈米線(ZnO-NWs)當作暫時性模板，製備出高透明度的二氧化矽奈米管陣列(SiO2-NT arrays)。本方法具有價格低廉、大面積製作、無需觸媒、製程溫度低等優勢。並且能夠利用ZnO-NWs直徑與長度鍍着薄膜厚度進行SiO2-NT的長度與內外部管徑寬度之調變。於n-GaN表面上製備具有3 μm長度之SiO2-NT arrays VLEDs結構，相較於表面只有KOH粗化之VLEDs，此方法製備之VLEDs光輸出功率在操作電流350 mA下增加60.4%。
再者，本研究亦於GaN-VLEDs表面製備IZO透明導電膜搭配二氧化矽奈米管陣列結構。一方面IZO作為n-GaN表面之電流擴展層，期使表面經KOH粗化之VLEDs具有更好的電流擴散；另一方面IZO透明導電膜與二氧化矽奈米管其折射係數(nIZO=2.1, nSiO2=1.5)介於n-GaN與空氣之間，可以有效地增加了光子析出角度，對元件之光輸出功率之改善有極大助益。相較於傳統表面僅使用KOH濕蝕刻粗化之VLEDs，此結合IZO透明導電膜與SiO2-NT陣列之VLEDs於操作電流350 mA注入下，光輸出效率增加103%，且順向電壓亦降低0.2 V。
最後，本研究提出具備高反射層與電鍍鎳基板以及撘配化學濕蝕刻置換GaAs基板，且於n+-GaAs layer上濺鍍透明導電膜IZO作為電流擴散層，製備高亮度金屬基板結構AlGaInP-LEDs，以解決傳統四元LED包括元件散熱不良、低光通量與發光不均等諸多方面的問題，期望可對新世代LED光源之開發提供助益。

In this study, efforts to enhance the light extraction and power conversion efficiency of vertical-structured GaN-based light-emitting diodes (VLEDs) and AlGaInP-LEDs employing nickel electroplating and laser lift-off (LLO) techniques were proposed. As compared to conventional lateral GaN-based LEDs with sapphire substrate (abbreviated as regular LEDs), GaN-VLEDs have good heat dissipation, shorter conduction path, less current crowding effect, and larger effective area through a conducting substrate and improved current spreading through the top of the n-GaN epilayer. However, the light-extraction efficiency of VLEDs must still be improved for general lighting. For the AlGaInP-LED structure, a high internal quantum efficiency of around 90% has been achieved for AlGaInP LEDs due to the rapid development of epitaxy technique. However, the absorbing and poor thermal conducting of conventional GaAs substrate have hindered the further application for large area, high power, and high-efficiency illumination. As a result, the thesis presents the novel fabrications to improve the light extraction efficiency of both GaN-VLEDs and AlGaInP-LEDs.
First, we aimed to further improve the light-extraction efficiency of regular VLEDs beyond previous work. Through the use of annealed-Pt/Al/Pt as a high reflectivity p-ohmic/mirror layer and polystyrene (PS) nano-spheres as a 2-D mask for producing a n-GaN surface and the patterned-deposition of indium-zinc-oxide (IZO), GaN-VLEDs with atop periodic nano-structure (VLED-A) were fabricated. At 350 mA, VLED-A exhibited a crucial VF reduction of 0.14 V with an enhancement of 97% in light output power (Lop) as compared to regular-VLED with KOH treatment.
Second, through a deposition of thin SiO2 film to sheathe the hydrothermally grown (HTG) ZnO nanowires arrays (ZnO-NW arrays), the high transparent SiO2 nanotube arrays (SiO2-NT arrays) with controllable inner/outer diameter and length were fabricated. The prepared SiO2-NT arrays with average inner/outer diameters and length of around 200/300 nm and 1.5 μm, respectively, exhibited a superior transmittance of 95% in visible light spectrum. In addition, surface roughness using SiO2-NT arrays on vertical-structure GaN-LEDs (VLEDs) showed an additional improvement in the light output of about 60.4% at 350 mA as compared to those of regular VLEDs with KOH treatment, suggesting the effectiveness and promising applications of the proposed SiO2-NT arrays in optics and optoelectronics devices.
Furthermore, the use of IZO transparent conduction layer (TCL) and SiO2 nanotube (SiO2-NT) arrays graded-refractive-index integrated structure to improve light extraction of vertical structure KOH-etched GaN-based light emitting diodes (VLEDs) is demonstrated. Compared with VLEDs without the proposed scheme, the proposed VLEDs show considerable gains in light emitted critical angle and light output power (Lop) by 21.2° and 103% at 350 mA, respectively.
Finally, employed IZO-TCL for metal substrate AlGaInP-LEDs was investigated with regard to both fabrication and effectiveness in improving light extraction efficiency. After the removal of the GaAs substrate, a metal system consisting of AuGe/Au was deposited to form ohmic contact dots for n+-GaAs and then IZO film was deposited to serve as a TCL. Compared to conventional LEDs with GaAs substrate, the proposed LEDs show an increase in light output power (i.e., ΔLop/Lop) by 116.7% at 20 mA and 168.9% at 100 mA.

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