利用有機金屬化學氣相沉積法在奈米圖型化基板上成長及製作高效率氮化銦鎵系列發光二極體元件

Abstract

氮化鎵系列光電元件可廣泛使用在不同波段之應用(從近紫到紅外)，並且可在高電場和高溫環境下持續操作，在近二十年來，我們可以清楚看到氮化鎵系列雷射(Laser)及發光二極體(LED)將持續改變我們每天日常生活。 在此研究中，為了要達到高效率發光二極體以及提升磊晶層之晶格品質，我們提出三種奈米技術來製備我們的基板 : 自組式氮化鎵奈米柱、嵌入式二氧化矽 (SiO2) 奈米遮罩蝕刻而成的奈米柱以及以矽基板製作而成的奈米柱。在本論文第一部分，我們結合射頻電漿分子束磊晶機台 (RF-plasma MBE) 以及有機金屬氣相磊晶機台 (MOCVD) 在藍寶石基板上先製造自組式氮化鎵奈米柱再成長高效率發光二極體，自組式氮化鎵奈米柱可藉由奈米級側向磊晶機制（NELOG）有效抑制缺陷，而在自組式氮化鎵奈米柱基板上製造出來的發光二極體比起一般發光二極體元件有較小的電激螢光光譜藍移現象，並在20mA電流操作下元件發光強度提升了70 %。 另外我們也成功使用嵌入式微米尺寸空氣柱及奈米尺寸二氧化矽 (SiO2) 遮罩製造高亮度發光二極體，埋入微米級空氣柱及奈米級二氧化矽 (SiO2) 遮罩在氮化鎵磊晶層中發現應力由1.73 GPa減小到 0.88 GPa，另一方面，由於改變在氮化鎵和藍寶石基板中折射率而觀察到高反射率，元件表現上比起一般發光二極體元件在20mA電流操作下發光強度提升了65 %。 最後，我們研究氮化鎵系列發光二極體成長在微米級與奈米級圖型化矽基板之材料、光和電特性研究，從材料量測發現成長在奈米級圖型化矽基板之磊晶品質比起微米級圖型化矽基板來的好；從光學量測發現成長在奈米級圖型化矽基板之發光磊晶層比起微米級圖型化矽基板有較好的載子侷限能力以及較高的載子複合速率；而在奈米級圖型化矽基板上製造出發光二極體元件有較小的電激螢光光譜藍移、較小的漏電流以及較少的效率驟降現象。 在本論文中，我們可以達成成長及製造高品質發光二極體元件，我們期許未來使用新穎奈米技術來有效提升氮化鎵系列光電元件。

GaN-based optoelectronic devices can be used in a wide range of applications due to its wide band gap coverage (from ultraviolet to infrared), sustainability of high electrical field, and high temperature operation. In the last two decades, we saw a strong demand of GaN-based lasers or light emitting diodes (LEDs), which will eventually change our daily life. In this study, in order to achieve high efficiency LEDs and enhance crystal quality of epitaxial layer, we adapted three nano-scale technologies to prepare our substrate: native grown GaN nanopillar, embedded SiO2 nano-mask etched nanopillar, and Si-based nanopillar. In the first part of the thesis, we presented a novel design of high-performance LEDs using a GaN nanopillars (NPs) structure grown on sapphire substrate by integrating RF-plasma molecular beam epitaxy (MBE) and metal–organic chemical vapor deposition (MOCVD). The GaN NPs suppress the threading dislocations effectively by nanoscale epitaxial lateral overgrowth (NELOG). The LEDs fabricated on the GaN NPs template exhibit smaller electroluminescent peak wavelength blue shift and great enhancement of the light output (70% at 20 mA) compared with the conventional LEDs. We also successfully demonstrated high bright LEDs with embedded microscale air voids and SiO2 nanomask. It was found that the residual stress was reduced from 1.73 to 0.88 GPa in the GaN epitaxial layer by inserting the microscale air voids and SiO2 nanomask. On the other hand, we observed strong reflectance modulations due to the different refractive indices between the GaN and sapphire. In addition, the NR-LEDs shows large enhancement of the light output (65% at 20 mA) compared with the C-LEDs. Finally, we investigate the material, optical and electrical characteristics of the GaN-based LEDs grown on micro- and nano-scale patterned silicon substrate (MPLEDs and NPLEDs). From material measurement, it indicates that the crystalline quality of the epitaxial structure fabricated on NPSi substrate is superior to MPSi substrates. From optical measurement, NPLEDs have better carrier confinement and higher radiative recombination rate than MPLEDs. In terms of device performance, NPLEDs exhibit smaller electroluminescence peak wavelength blue shift, lower reverse leakage current and decrease in efficiency droop when compared with the MPLEDs. In this dissertation, we can achieve the studies on the growth of high crystal quality and fabrication high performance LEDs devices. We hope using novel nanotechnology to be effective for improving the quality of GaN-based optoelectronic devices in future.