本論文中，為了改善氮化鎵(GaN)系發光二極體(LEDs)的磊晶品質，我們提出利用陽極氧化鋁(anodized aluminum oxide，AAO)薄膜來圖形化藍寶石基板，並應用此奈米級圖形化基板來有效地提升氮化鎵系發光二極體的磊晶品質；首先，我們提出在藍寶石基板上製備陽極氧化鋁薄膜，藉由調變氧化時的參數來改善多孔性陽極氧化鋁薄膜的孔徑大小和排列規則度；接著應用此多孔性陽極氧化鋁薄膜來製備陽極氧化鋁奈米孔洞圖形化基板(anodized aluminum oxide-nanoporous patterned sapphire substrate，AAO-NPSS)，並以此基板磊晶成長氮化鎵系發光二極體，並做一系列材料分析與元件光電性量測，深入且詳細地探討磊晶品質與光電特性改善之結果。
於陽極氧化鋁薄膜的研究中，我們成功地於藍寶石基板上成長出具有規則性的多孔性陽極氧化鋁薄膜。首先我們在藍寶石基板上熱蒸鍍上一層鋁薄膜，並使用草酸當作電解液，接著於鋁薄膜上外加偏壓進行陽極氧化，製作出具有多孔性的陽極氧化鋁薄膜，並利用陽極氧化參數調變來改善陽極氧化鋁薄膜之品質。於本研究中吾人利用調變擴孔時間改善陽極氧化鋁薄膜孔徑過小的問題；並利用二次陽極氧化來改善孔洞之間排列的規則度；此外，為了加快製備速度與方便性，我們利用氫氧化鈉與氧化鋁反應快速的特性，選其作為陽極氧化鋁孔洞移除之溶液，以有效地降低規則性陽極氧化鋁薄膜之製備時間。
此外，由於氮化鎵與藍寶石基板間晶格不匹配導致大量線差排(threading dislocation)產生，在陽極氧化鋁奈米孔洞圖形化基板應用於氮化鎵發光二極體的研究當中，我們利用了乾蝕刻的方式成功地將多孔性陽極氧化鋁薄膜上的高規則性奈米孔洞圖形轉移至藍寶石基板上，製作出了奈米級的圖形化基板(patterned sapphire substrate)，此奈米級圖形化基板可有效地降低氮化鎵磊晶層中的線差排密度，大幅提升磊晶品質，減少非輻射復合（non-radiative recombination）的熱消耗，進而改善發光二極體的發光效率。在材料分析當中，我們從穿透式電子顯微鏡(TEM)剖面圖中驗證出使用陽極氧化鋁奈米孔洞圖形化基板所成長出的氮化鎵磊晶層可有效降低線差排的產生；我們亦從掃描式電子顯微鏡(SEM)中觀察到在氮化鎵磊晶層和奈米級圖形化基板之間有微小的空氣孔洞(air voids)的產生，此空氣孔洞可反射向基板發散之出光，有效地增加光萃取率(light extraction efficiency)；於拉曼(Raman)頻譜分析中亦可發現使用陽極氧化鋁奈米孔洞圖形化基板所成長出的氮化鎵磊晶層波數(wavenumber)有明顯的藍移現象，此乃因為磊晶層間晶格不匹配所引發的應力受到釋放；另外在X光繞射分析(XRD)中發現使用陽極氧化鋁奈米孔洞圖形化基板所成長出的氮化鎵磊晶層於(0002)面有較小的半高寬(FWHM)，此結果亦再次證實磊晶品質的改善。在電性與光性的分析中，我們發現應用陽極氧化鋁奈米孔洞圖形化基板所成長之發光二極體於光性特性與外部量子效率皆有明顯地提升且順向導通電壓亦可有效地改善。最後於可靠度分析中，經過1000小時的測試，使用陽極氧化鋁奈米孔洞圖形化基板的發光二極體元件於可靠度部分亦獲得改善。

In this thesis, in order to enhance the crystalline quality of gallium nitride (GaN)-based light-emitting diodes (LEDs), a nanoporous anodized aluminum oxide (AAO) thin film was used to pattern sapphire substrate, which can effectively improve crystalline quality of GaN epitaxial layer. First, we introduce an AAO thin film grown on a sapphire substrate with a highly-ordered pores arrangement by modulating conditions of anodization. After that, the AAO nanoporous pattern was transferred on a sapphire substrate by inductively coupled plasma (ICP) etching process. And we used this anodized aluminum oxide-nanoporous patterned sapphire substrate (AAO-NPSS) to enhance the crystalline quality of GaN-based LEDs. The material analyses as well as optical and electrical characteristics were also studied and discussed.
In the study of nanoporous AAO thin film, the regular AAO thin film is successfully grown on a sapphire substrate. Firstly, a thin aluminum layer was evaporated on a sapphire substrate by a thermal evaporator. Oxalic acid was chosen as the electrolyte. Then, the thin aluminum layer was anodized by applying bias voltage. Finally, parameters of anodization were modulated to improve the quality of AAO thin film. In this study, pore widening time was increased to figure out the problem that pore diameters of AAO were too small. In addition, a two-step anodization approach was applied to improve the regularity of pores arrangement. Lastly, in order to shorten the fabrication time and increase convenience of anodization of the highly-ordered AAO thin film, sodium hydroxide (NaOH) solution was utilized as the removing solution.
Because of lattice mismatch and remarkable difference in thermal expansion coefficient between sapphire substrate and GaN, highly compressive stress, which is induced with the decrement of growth temperature, leads to many threading dislocations (TDs) on GaN epitaxial layers. These TDs seriously deteriorate device performance and reliability. Hence, in order to alleviate this problem, the employment of AAO-NPSS is used to reduce strain and dislocation density as well as significantly improve the light extraction efficiency (LEE). In the material analyses, from the comparison of transmission electron microscopy (TEM) images, TDs could be reduced by using an AAO-NPSS. In addition, air voids were also formed between GaN layers and the AAO-NPSS. The formation of air voids could reflect photons emitted from MQW upward to top direction rather than be absorbed by bottom package metal. Photons could experience more opportunities to be extracted outside. Moreover, the blueshift phenomenon could also be observed in Raman spectra analyses which could be attribute to the strain relaxation. Most importantly, the studied device exhibits smaller full width half maximum in X-ray diffraction (XRD) spectrum. This result has once again confirmed that crystalline quality of GaN epitaxial layers could be improved by using an AAO-NPSS. As compared with a conventional LED, at 20 mA, the studied device exhibits 52.8% and 43.3% enhancements of light output power (LOP) and external quantum efficiency (EQE), respectively. Substantially, the reduced leakage current and decreased turn-on voltage are also achieved. Reliability of the studied device could also be improved. Therefore, the studied AAO-NPSS shows the promise to fabricate high-performance GaN-based LEDs.

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