三五族氮化物之成長與應用

Abstract

本篇論文研究了自氮化鎵基板的V型凹點的位置點控制了氮化銦的晶體成長。氮化鎵晶體利用在藍寶石基板上之已經圓盤狀圖案化的二氧化矽側向成長氮化鎵磊晶層來製造V型凹點。其中發現氮化銦晶體擇優選在V型凹點的傾斜的{10-11}晶面上生長。一個微米尺度或者更小的V型凹點之尺寸可以在V型凹點底部提供精確的位點控制的氮化為銦原子成核，而在其餘的暴露的氮化鎵表面上卻沒有成長氮化銦晶體。而位置點控制的成核作用歸因於在V型底部匯聚的六個{10-11}晶面產生的低表面能態點。當銦原子來源供應低於某一數值時，該V型凹點的底部是能夠聚集足夠的活性源以開始成核反應，從而提供位置點控制晶體成長的唯一位置。

本篇論文研究兩種類型之具有空氣間隙冠狀結構的紫外光發光二極體在典型的氮化鋁鎵材料透過金屬有機化學氣相沉積來製作與研究。模擬結果表示，所提出的1.5微米冠狀圖案化藍寶石基板製作之紫外發光二極體在中心波長369奈米，可以具有更好的元件性能。將空氣間隙之結構導入氮化鋁鎵發光二極體的概念因而提高光萃取效率的能力已是眾所皆知。基本上使用蒙地卡羅方法的光學模擬工具來分析光萃取效率，並且製作實際的光電元件在實驗當中進一步驗證光線追踪之模擬結果。由蒙地卡羅射光線追踪的模擬結果顯示，由於空氣間隙的強光反射和重新定向，具有空氣間隙的發光二極體結構的光萃取效率將會顯著增加。這種高效能的氮化鎵發光二極體是由金屬有機化學氣相沉積機台來製作。在穿透式電子顯微鏡的影像分析結果顯示磊晶側向成長可以有效抑制晶體線缺陷之過度成長。蒙特卡羅光線追踪模擬結果顯示，由於空氣間隙的強光反射和重新定向，嵌入空氣隙結構的發光二極體之光萃取效率也將顯著增加。

本篇論文在圖案化藍寶石基板的微結構幾何形狀對於氮化鎵發光二極體的光萃取效率的影響進行數值分析。研究了各種尺寸的錐形結構以及穹頂和混合式等微結構。發現光萃取效率主要是取決於微結構的表面斜率。光萃取效率隨著斜率迅速上升，並且當斜率超過0.6時變平。然而縮小微結構對於光萃取效率則幾乎沒有影響。與在平坦基板上成長的發光二極體相互比較，發現光線在圖案化藍寶石基板的發光二極體中行進更長的距離。因此保持氮化鎵的吸收損耗低對於光萃取效率的優化是重要的。

A site-controlled crystalline InN growth from the V-pits of a GaN substrate was investigated. The V- pits were fabricated by epitaxial lateral growth of GaN over SiO2 disks patterned on a sapphire substrate. InN crystals were found to preferably grow on the inclined {10-11} crystal planes of the V-pits. A V-pit size of 1 μm or less can provide precise site-controlled InN nucleation at the V-pit bottom, while no InN was grown on the rest of the exposed GaN surfaces. The site-controlled nucleation is attributed to the low surface energy point created by the converging six {10-11} crystal facets at the V-pit bottom. When In source supply is below a certain value, this V-pit bottom is the only location able to aggregate enough active sources to start nucleation, thereby providing site-controlled crystal growth.

We report two types of crown-shaped with air void in a typical AlGaN-based ultraviolet light-emitting diode (UV-LEDs) with embedded air void array grown by metal–organic chemical vapor deposition are fabricated and investigated. The simulation results demonstrate that the proposed 1.5μm crown-shaped patterned sapphire substrates (CPSS) UV-LEDs (λ~369nm) have better device performances. The concept of introducing air-void structures into AlGaN-based LEDs is well recognized for its ability to enhance the light extraction efficiency (LEE). The LEE analyzed using optical simulation tools based on Monte Carlo method and the ray-tracing simulation results are further validated experimentally by fabricating real devices. The Monte Carlo ray-tracing simulation reveals that the light extraction of the air-voids embedded LED was dramatically increased due to a strong light reflection and redirection by the air voids. The high performance GaN based light-emitting diodes (LEDs) with embedded air void array grown by metal–organic chemical vapor deposition (MOCVD). The transmission electron microscopy images demonstrate that the threading dislocations were significantly suppressed by epitaxial lateral overgrowth (ELOG). The Monte Carlo ray-tracing simulation reveals that the light extraction of the air-voids embedded LED was dramatically increased due to a strong light reflection and redirection by the air voids.

The influence of the microstructure geometry of patterned sapphire substrates (PSS) on the light extraction efficiency (LEE) of GaN LED is numerically analyzed. Cone structures of various dimensions are studied, along with dome and mixed microstructures. LEE is found to mainly depend on the microstructure surface slope. LEE rises quickly with slope and flattens out when the slope exceeds 0.6. Scaling down the microstructure has little effect on LEE. Light rays are found to travel longer distances in PSS LEDs, as compared with LEDs grown on a flat substrate. Keeping GaN absorption loss low is important for LEE optimization.