應用氧化鋅與二氧化矽共濺鍍漸變折射率薄膜於具網狀結構氮化鎵發光二極體元件之特性研究

Abstract

本論文主要探討應用氧化鋅(ZnO)與二氧化矽(SiO2)共濺鍍漸變折射率薄膜於具網狀結構氮化鎵發光二極體元件上，期望能有效降低氮化鎵與空氣間因折射係數值的巨大差異所造成的全反射效應與菲涅爾損失。 首先本論文利用磁控濺鍍系統，以共濺鍍方式成功濺鍍出ZnO/SiO2漸變折射率薄膜。實驗結果顯示，藉由調變ZnO與SiO2的濺鍍功率能有效控制共濺鍍漸變折射率薄膜的折射係數值，使其介於ZnO(n=2.05)與SiO2 (n=1.46)之間。 本論文接著製作不同網格大小/間距比例之網狀p型氮化鎵發光二極體元件，利用網狀結構降低氮化鎵與空氣間因折射係數值的巨大差異所造成的全反射效應，改善元件的光輸出功率。實驗結果顯示，在20mA工作電流下，Planar ITO LED與LED-P(5/5)的光輸出功率分別為6.57mW與7.81mW。LED-P(5/5)比Planar ITO LED提升了18.8%的光輸出功率。 延續前面的實驗成果，本論文將ZnO/SiO2共濺鍍漸變折射率薄膜應用於網狀p型氮化鎵發光二極體元件上，利用漸變折射率薄膜降低氮化鎵與空氣間因折射係數值的巨大差異所造成的全反射效應與菲涅爾損失。實驗結果顯示，在20mA工作電流下，Planar ITO LED、LED-P0與LED-P3的光輸出功率分別為6.57mW、7.81mW、8.72mW。LED-P0與LED-P3分別比Planar ITO LED提升了18.8%與32.7%的光輸出功率。而比較LED-P0與LED-P3後發現，共濺鍍漸變折射率薄膜能有效幫助提升元件之光輸出功率約13.9%。 最後，本論文將ZnO/SiO2共濺鍍漸變折射率薄膜應用於網狀量子井氮化鎵發光二極體元件上，利用漸變折射率薄膜降低氮化鎵與空氣間因折射係數值的巨大差異所造成的全反射效應與菲涅爾損失。實驗結果顯示，在20mA工作電流下，Planar ITO LED與LED-W2的光輸出功率分別為6.57mW、8.78mW。LED-W2比Planar ITO LED提升了33.6%的光輸出功率。

This study presents a comparison between the performance of Planar ITO light emitting diodes (LEDs) and GaN-based mesh-typed LEDs with ZnO/SiO2 co sputtering graded refractive index (GRIN) film. The finding shows that it substantially diminishes the effect of total internal reflection and reduces the Fresnel loss by narrowing the refractive index difference between GaN and air. The deposition of ZnO/SiO2 is performed by co sputtering GRIN films on a sapphire substrate using RF-magnetron sputtering. The results show that changing the deposition rate ratio of (ZnO/SiO2) causes the refractive index of these co sputtering films to vary between 1.46 and 2.05. To improve the output power, we fabricate meshed p-GaN LEDs with various strip width/spacing to diminish the total internal reflection caused by large refractive index differences between the GaN and air. Using a 20 mA injection current, the output powers are 6.57mW and 7.81mW for Planar ITO LED and meshed p-GaN LED (LED-P(5/5)), respectively. The 20 mA LED output power of LED-P(5/5) is 18.8% greater than Planar ITO LEDs. This is attributable to greater light extraction efficiency for the meshed p-GaN LED, associated with a higher probability of photons escaping from the surface. In addition, the meshed p-GaN LEDs with ZnO/SiO2 co sputtering GRIN film are fabricated to reduce the total internal reflection and Fresnel loss. Using a 20 mA injection current, the output powers are 6.57mW, 7.81mW, and 8.72mW for the Planar ITO LED, meshed p-GaN LED (LED-P0), and meshed p-GaN LED with GRIN film (LED-P3), respectively. The 20 mA LED output powers of LED-P0 and LED-P3 are 18.8% and 32.7% greater than the Planar ITO LED, respectively. This is attributable to the greater light extraction efficiency of the meshed p-GaN LED with ZnO/SiO2 co sputtering GRIN film, associated with a higher probability of photons escaping from the surface. The output power difference between the LED-P0 and LED-P3 also indicates that GRIN film enhances light output power by 13.9%. Finally, we fabricate meshed MQW LEDs with ZnO/SiO2 co sputtering GRIN film to achieve greater light extraction efficiency. Using a 20 mA injection current, the output powers are 6.57mW and 8.78mW for the Planar ITO LED and meshed MQW LED with GRIN film (LED-W2), respectively. Compared with the planar ITO LED, the LED-W2 enhances the 20 mA output power by 33.6%. This is attributable to the greater light extraction efficiency for the meshed MQW LED with ZnO/SiO2 co sputtering GRIN film, associated with a higher probability of photons escaping from the surface.