以氮化鋁作為電流阻擋層之氮化鎵微共振腔發光元件以及其光學模態分析之研究

Abstract

本篇論文旨在探討改善氮化鎵微共振腔發光元件特性的製程技術。以期能夠成功製作出電激發氮化鎵面射型雷射。 首先，透過在量子井上成長氮化鋁，做為混合式布拉格反射鏡氮化鎵微共振腔結構的電流阻擋層，取代過去只有成長氮化矽在在p 型氮化鎵上做絕緣層的方法，以期達到更加的電流侷限效果以及側向的光學侷限。更設計了環型的透明導電層取代原先的圓型透明導電層，希望能減少共振腔內部的損耗。透過與傳統結構做比較，我們發現在同樣電流注入下發現雖然插入氮化鋁結構的元件有稍微高的串聯電阻，但是在光輸出強度卻有更佳的表現;並且在光譜的量測下得到氮化鋁結構（1100）有較傳統結構(650)高的共振腔品質因子，以及側模的量測結果符合模擬預期都在在地證明了我們的假設。 接著，由於考慮到了藍寶石基板本身的電導率和熱傳導率不佳，以及氮化鎵-氮化鋁布拉格反射鏡的製作控制困難。我們採用了雷射剝離技術製作雙介電質布拉格反射鏡搭配氮化鋁電流阻擋層的電激發微共振腔發光元件。在元件複雜的製作完成之後，我們量測元件得到了一個高(226)的共振腔品質因子，雖然沒有達到電激發雷射操作，但確實證明了此種設計製作的可行性，並且在最後提出元件可改良以及最佳化的方向。

The purpose of this thesis is to discuss the improvement on the process of GaN-based MCLED so that we can successfully fabricate a laser lift-off GaN-based MCLED. At first, we formed a GaN microcavity of hybrid Bragg reflector with a current blocking layer by growing AlN on the quantum well instead of growing SiN on the p-GaN conventionally in order to achieve a better current confinement and lateral optical confinement. Additionally, we designed a ring-shape transparent contact layer in replace of the original round-shape one to reduce the internal loss of the resonant cavity. Compared to the conventional structure, the device into which the AlN current blocking layer had been inserted showed a slightly higher series resistance but a better light output. Furthermore, the fact that the Q factor of the AlN layer was measured to be higher (1100) than that of the conventional one (650) and that the simulation result of the transverse mode was correspondent with our expectation both verified our hypothesis. Finally, to modify the intrinsic property of the sapphire substrate (poor electric and thermal conductivity) and to overcome the difficulty in the process of the AlN/GaN DBR, we used the laser lift-off technique to fabricate a MCLED with two dielectric DBRs and an AlN current blocking layer. After the complicated fabrication process, we obtained a high Q factor (226) from the device. Even though we did not achieve the laser operation, we have proved the feasibility of this method and gave some suggestion to improve and optimize the fabrication.