因應紫外光應用的需求，氮化物發光二極體(light-emitting diodes)的效率需要進一步提升，但是氮化物材料系統於紫外光發光區的材料特性讓其在元件效率的提升上尤其困難。本論文主要為應用能帶工程技術、化學蝕刻與粗化/圖案化基板來改善氮化物紫外光發光二極體之特性。論文首先針對長波長區段之紫外光發光二極體進行探討，接著為了實現短波長區段之紫外光發光二極體，先針對成長高品質氮化鋁/藍寶石基板作研究。研究包含：四元氮化物材料應用、晶粒背面粗化、電子阻障層之設計、選擇性參雜、及圖案化基板之影響。本論文透過有機金屬化學氣相沉積法來成長紫外光發光二極體磊晶層及元件，並藉由理論模擬(SiLENSe, STR Crop.)來探討這些物理現象，且經由結構上的改善來降低諸如極化場等的不利因素影響。
利用對氮化鎵基板背面粗化可有效提升元件之光取出效率。氮化鎵基板的穿透率受蝕刻時間影響而有所不同，同時，穿透率亦和波長有極大關係。應用背面粗化之氮化鎵基板，藍光及近紫外光發光二極體之發光強度較成長於未粗化氮化鎵基板的發光二極體分別提升21%及94%。其中，光取出效率在蝕刻之六角錐長寬較小且密度較高時為最佳，因此，元件之發光強度在以短蝕刻時間(一分鐘)為最佳，在20毫安培電流注入下可得到107%的提升。
降低極化場的影響可提升元件的內部量子效率(internal quantum efficiency)。我們藉由使用晶格常數匹配之四元氮化物材料及漸變式電子阻障層來降低極化場的影響。在成長四元化合物材料時，三甲基鎵(trimethylgallium, TMGa)的流量會影響銦和鋁的融入率；當傳統氮化鎵能障為In0.035Al0.089Ga0.876N四元氮化物取代時，光輸出功率在100毫安培電流注入下約提升15.9%。第二部分，使用鋁含量漸近式電子阻障層時，紫外光元件發光強度在350毫安培電流注入下提升1.87倍。透過對電子阻障層巧妙的設計，可以提高對電子的阻擋程度並提升電洞注入能力。第三部分，選擇性能障參雜會影響載子濃度分佈，並降低非輻射複合程度，此改善之情形在高缺陷密度下尤其顯著。
使用異質接面橫向磊晶成長法可有效降低氮化鋁基板之缺陷密度。在改變藍寶石基板上之氮化鋁圖案化基板的形狀時，氮化鋁的結晶品質、表面形貌、接和時間及臨界厚度皆會受影響。

Adopting nitride-based ultraviolet light-emitting diodes (UV LEDs) to achieve light output efficiency depends on pushing efficiency toward practicable levels. However, the material properties of the III-nitride material system have made further progress toward shorter wavelength increasingly difficult. This dissertation mainly aims to improve the efficiency of nitride-based UV LEDs by using band engineering techniques, the chemical etching process, and patterned substrates. In the beginning we focused our attention on long wavelength UV LEDs, and then made the effort to grow high quality AlN/sapphire templates for short wavelength UV LEDs. Investigating light output power (LOP) efficiency improvement techniques includes employing a quaternary material, backside roughening of chip, electron blocking layer (EBL) design, selective doping, and different patterns of the AlN/sapphire form. Light emitters are fabricated using the metalorganic chemical vapor deposition (MOCVD) system. Physical phenomena are studied through the design of device structures using numerical simulations (SiLENSe, STR Crop.). The influence of detrimental effects, such as the polarization effect, is considerably reduced by using these redesigned structures.
An increase in light extraction efficiency is obtained by using a roughened backside GaN substrate. The transmittance of the GaN substrate is affected by etching time and strongly depends on the wavelength. When the roughened backside structure is used, the output powers of the blue and near-UV LEDs increase by 21% and 94% compared with LEDs, which are fabricated without the wet etching process. Light passes through the shortened vertical length and the high density of hexagonal pyramids can be effectively extracted. Hence, the output power of near-UV LED with a short etching time (1 min) increases by 107% at 20 mA.
An increase in internal quantum efficiency is obtained by reducing the effect of the polarization fields. These fields are approached by employing the lattice match quaternary material and the gradient Al composition EBL. Regarding the growth of the quaternary material, incorporating In and Al is influenced by the trimethylgallium (TMGa) flow rate. Accordingly, an enhancement of 15.9% in LOP is obtained from the measurements at 100 mA when the GaN barrier layers are replaced with In0.035Al0.089Ga0.876N barier layers. In the second part, the LOP of UV LEDs with gradient Al composition is 1.87 times higher than that of the conventional structure at 350 mA. The delicately designed EBLs capably perform the electron blocking function and eliminate the incidental drawback of obstructing the hole injection caused by the nature of the large polarization field at the c-plane nitride heterojunction. In the third part, selective doping provides hints that the dopant in the barriers can modify carrier concentration and change the nonradiative recombination rate, particulary under high dislocation condition.
The threading dislocation density of the AlN template is reduced via the epitaxial lateral overgrowth growth (ELOG) process. A lateral epitaxial overgrowth leads to a remarkable reduction in threading dislocation. A variation of differently patterned structures indicates that, the form of the pattern affects the crystal quality, surface morphology, coalescence time, and critical thickness of AlN before cracking.

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