本篇論文我們使用藍寶石基板來製作圖形化之基板。一般而言，氮化鎵磊晶層通常是成長在藍寶石基板上，這是因為沒有適當的基板可供氮化鎵異質結構成長。由於氮化鎵磊晶層與藍寶石基板之間存在著不同的晶格常數與溫度膨脹係數，所以在氮化鎵磊晶層裏存在著許多的穿透差排，雖然利用低溫成長的氮化鎵或氮化鋁緩衝層可以改善氮化鎵磊晶層的結晶品質，但還是有109-1010 cm-2的穿透差排密度存在於氮化鎵磊晶層裏。

　　為了減少穿透差排密度，有許多的方法被提出，例如磊晶側向再成長、懸垂式磊晶層與圖形化藍寶石基板，相較於磊晶側向再成長方式，利用有機金屬化學氣相沉積之圖形化藍寶石基板方法只需要一次磊晶成長，因此圖形化藍寶石基板方法應該更容易成長高品質的氮化鎵磊晶層。

　　我們利用一般的黃光及電感耦合式電漿蝕刻製程來製作圖形化藍寶石基板，並且以低壓之有機金屬化學氣相沉積法來成長有圖形化及沒圖形化藍寶石基板發光二極體。我們利用高解析度X光繞射光譜之半高寬與穿透式電子顯微鏡之影像來評估氮化鎵磊晶層的結晶品質，根據X光繞射光譜之半高寬與穿透式電子顯微鏡之照片顯示，圖形化藍寶石基板其氮化鎵磊晶層之穿透差排密度比不做圖形化藍寶石基板之穿透差排密度為低，這樣的結果說明我們可以利用圖形化藍寶石基板來改善氮化鎵磊晶層的結晶品質。此外可發現，圖形化藍寶石基板的電激發光光譜峰值強度與輸出功率比不做圖形化藍寶石基板分別大於34.4%與26%，藉由改善結晶品質與圖形化基板所散射的光，可增加發光二極體的輸出功率。當發光二極體操作在室溫及順向電流20 mA時，對於六角形圖案之基板其輸出功率與外部量子效率是11.24 mW與20.85%，長條狀圖案之基板為11.02 mW與20.44%，而沒有圖形化之基板為8.89 mW與16.49%。而在壽命測試方面，連續測試208小時後，有圖形化與沒有圖形化之藍寶石基板其輸出功率分別減少27.5%與41.8%。此外，比起不做圖形化之藍寶石基板，有圖形化之藍寶石基板其接面溫度與熱阻抗較小。

　In this thesis, we have fabricated the pattern on substrate by using sapphire substrate. In generally, the GaN epilayers are usually grown on the sapphire substrate, because there is no large substrate available for GaN heterostructure growth. Due to the large differences in the lattice constant and thermal expansion coefficient between GaN epitaxials and sapphire substrate, numerous threading dislocations are induced in the GaN epilayers. Although the introduction of low temperature GaN or AlN buffer layer can significantly improve the crystal quality of the GaN epitaxial layer. The threading dislocation density has been reported to be of the order of 109-1010 cm-2 in the GaN epitaxial layer.

　In order to reduce the dislocation density, there are many methods to be reported such as epitaxial lateral overgrowth (ELOG), pendeoepitaxy (PE) and patterned sapphire substrate (PSS). It shall be noted that one only need to perform metalorganic chemical vapor deposition (MOCVD) growth once in the PSS, as compare to twice in ELOG. Thus, it shall be easier to grow high quality GaN epilayers on the PSS, as compare to perform ELOG.

　The PSS structure was fabricated by using standard photolithography and inductively coupled plasma. The growth of PSS and NSS LEDs were carried out using a low-pressure MOCVD. The crystal quality of GaN epilayer was estimated from full-width at half-maximum (FWHM) high-resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM). According to FWHM of HRXRD and TEM micrographs, the dislocation densities of GaN epilayer grown on the PSS were lower than that of on the NSS. Such a result indicates that we could improve crystal quality of GaN epilayer by using PSS. It was found that the EL peak intensity and output power of PSS were about 34.4% and 26% larger than that of NSS, respectively. The increase in the output power was achieved by improving the crystal quality and scattering emission light from pattern. When the LEDs was operated at a forward current of 20 mA at room temperature, the output power and the external quantum efficiency were estimated to be 11.24 mW and 20.85% for hexagonal pattern , 11.02 mW and 20.44% for striped pattern, and 8.89 mW and 16.49% for without pattern, respectively. The output intensities decayed by 27.5% and 41.8% after 208 hrs burn-in for PSS and NSS, respectively. In addition, the PSS owns smaller junction temperature and thermal resistance compare with the NSS.

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