覆晶式發光二極體光萃取效率提升之研究

Abstract

在此研究當中，我們基於氮化鎵覆晶式發光二極體(Flip-Chip LEDs)的製程條件上做優化，希望能從以光萃取效率為長的覆晶式發光二極體，探討不同結構的光萃取效率。第一部分的研究為改善覆晶元件之反射電極並製作具有良好歐姆接面與不同反射率條件的反射電極，在p型氮化鎵(p-type GaN)材料上進行反射率歐姆接觸電極之製作，其架構包含:歐姆層(透光率高與好的歐姆接觸)、反射層(具高反射率)、阻擋層(有效的阻擋金屬互相擴散)，不同的金屬結構組合不但可以得到低的歐姆接觸電阻，並且可以提供不同的反射率，可藉由不同反射率電極探討反射率與光萃取效率之間的關係。製作電極的條件乃是，蒸鍍金屬材料後藉由一次高溫回火達到歐姆接面與高反射率條件的電極，我們嘗試的反射電極金屬經熱處理過後，都可以達到不錯的歐姆接觸特性，特徵接觸阻值(specific contact resistance)在10-2ohm-cm2等級，且對應在藍光 450nm 的反射率可以達到93.6%，最後我們結論可得到應用上較佳的反射率電極製作。 第二部分中，我們利用不同形狀且不同尺度的圖形化氧化鋁基板，比較圖形化氧化鋁基板對覆晶式發光二極體的光萃取效率之影響，在相同製程下製作出相同電性的氮化鎵覆晶發光二極體，藉由電性量測、光強度以及搭配Rigorous Coupled-Wave Analysis模擬方法，得到不同的圖形化氧化鋁基板對光萃取的優劣，最後得到適合覆晶式發光二極體的圖形化藍寶石基板。

In this study, we change the process of GaN-based flip chip light-emitting diodes (LEDs), we want to investigate the light extraction efficiency of flip-chip LEDs. The first part of the study is to improve the reflective electrode of the flip-chip light-emitting diodes and produce a ohmic contact with the p-type GaN. Materials architecture of reflective contact metal includes: ohmic layer (high transmittance and ohmic contact), the reflective layer (light extraction), the barrier layer (block the diffusion of metals), different thickness of contact metal can get low resistance of ohmic contact, and provide different reflectance, discuss the relationship between the reflectance and the light extraction efficiency by the different reflectivity of p-contact electrodes. We try to produce high reflectivity electrode after the heat-treated, also achieve a ohmic contact (specific contact resistance) in the 10-2ohm-cm2 level, and corresponding to 93.6% of reflectance in the 450nm wavelength. We can get a better reflectivity electrode in application. The second part, we use patterned sapphire substrate of different shapes and scales to investigate the light extraction efficiency of flip-chipLEDs. Using the same process to produce flip-chip LEDs, and then discuss by I-V curve, light intensity and the simulation by rigorous coupled-wave analysis method, to get the light extraction of different patterned sapphire substrates. Finally we can derive suitable patterned sapphire substrate for flip-chip light emitting diodes.