利用奈米圖型化基板製作高效率氮化鎵發光二極體

Abstract

在此論文當中，我們提出於氮化鎵與藍寶石基板接面製作二氧化矽奈米柱陣列，以提高氮化鎵發光二極體發光效率。藉由穿透式電子顯微鏡剖面圖可觀察到氮化鎵在側向成長過程中，氮化鎵與藍寶石基板接面所形成的空氣洞以及氮化鎵中的Stacking fault有效地減少穿透缺陷密度，此外我們分別從X光繞射及光激發量測從得知氮化鎵磊晶品質有所改善，相較於傳統氮化鎵發光二極體，出光強度及內部量子效率都有所提升，利用此方法可增加光萃取效率及改善氮化鎵磊晶品質。 論文第二部分中，我們展示利用具有二氧化矽側壁保護的氮化鎵奈米柱陣列，製作出高品質及少量殘餘應力的兩吋獨立式氮化鎵基板，並藉由側向成長機制將氮化鎵奈米柱彼此接合而形成氮化鎵薄膜，相較於傳統氮化鎵發光二極體成長在藍寶石基板上，成長於獨立式氮化鎵基板具有低穿透缺陷密度以及較好的散熱能力，此外，利用獨立式氮化鎵基板可減少成長氮化鎵過程中應力的產生，並降低在變電流過程中電激發頻譜峰值的藍移及效率遽降的現象，電激發內部量子效率有26.8%的增益。

In this thesis, we investigated high efficiency InGaN/GaN light emitting diodes (LEDs) grown on sapphire substrate with SiO2 nanorod-array (NRA). The transmission electron microscopy images suggested that the voids between SiO2 nanorods and the stacking faults introduced during the nanoscale epitaxial lateral overgrowth (NELO) of GaN can effectively reduce the threading dislocation density. The GaN film showed improvement in crystal quality through x-ray diffraction FWHM and photoluminescence measurement. The light output power and internal quantum efficiency of the fabricated LED were enhanced compared to those of conventional LED. The improvements could be attributed to both the enhanced light extraction by utilizing SiO2 NRA and the improved crystal quality through the NELO method. In the second part, we demonstrated a method for fabricating 2 in. freestanding GaN substrates of high crystallographic quality and low residual strain. Arrays of GaN nanorods with SiO2-passivated sidewall were randomly fabricated on the sapphire substrate as growth seeds. The SiO2-passivated sidewall prevents the coalescence of GaN grains in spaces between the rods, causing them to grow preferentially on the top of individual rods. GaN LEDs grown on free-standing GaN substrate can reduce threading dislocation density and provide better thermal dissipation compared to that grown on sapphire substrate. Moreover, the reduction of strain by using free-standing GaN substrate results in smaller blue shift of current-dependent EL spectrum and efficiency droop. The EL IQE improvement of GaN-based LEDs grown on free-standing GaN was 26.8%