以二氧化矽奈米粒子小球製作氮化鎵奈米柱發光二極體及其特性分析

Fabrication and Analysis of GaN-based Nanorod Light Emitting Diodes

王振印(Cheng-Yin Wang)

指導教授 ： 黃建璋

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.02769

摘要

自90年代p型氮化鎵材料發展完備之後，氮化鎵目前為短波長發光二極體所廣泛應用的材料。發光二極體具有低耗電、使用壽命長、依賴性高、反應時間短等優點。儘管如此，在一些層面上面仍有許多發展空間，像是發光效率以及Quantum Confined Stark Effect所造成的波長漂移等議題。在本篇文章中介紹具有實用價值的奈米小球微影術方法來製作表面粗化氮化鎵發光二極體。由於發光二極體材料與空氣的折射係數差異極大，在發光二極體與空氣界面上易發生全反射，造成外部量子效應極低。目前解決的方式是在長晶過程當中額外生長粗糙層來降低全反射，不過這需要額外的時間及成本去完成。本篇文章中藉由旋塗及浸潤的方式，在發光二極體表面鋪排單層奈米粒子小球當作p-type GaN表面蝕刻遮罩，表面粗化發光二極體便可製作而成。相對於傳統發光二極體來說，無論是p-type GaN 或是ITO 表面粗化的發光二極體皆可展現具有相當程度的效能增加，且表面粗化製程不會影響到元件的電性特徵。這結果顯示奈米小球微影術提供一種不需額外增加製程的低成本方式製作高效能表面粗化發光二極體且此方法十分具有發展性。
波長漂移部分普遍的解決方式也是以在長晶過程中成長奈米結構去釋放材料中的應力。我們更進一步使用自組排列的奈米小球去製作自組性奈米柱結構氮化銦鎵/氮化鎵多重量子井發光二極體。有別於傳統長晶法，提供了另一種新方式在製程上解決波長漂移，也由於在奈米柱陣列製作並聯電極具有一定難度，僅有少數相關研究結果。奈米柱陣列由鋪排好的二氧化矽小球自然曝光，接著以乾蝕刻製程來完成。以一層SOG材料填充在奈米柱間的空隙來當作絕緣層，隔絕彼此平行的奈米柱二極體單元。電激發光螢光頻譜顯示奈米柱發光二極體的放光波長在注入電流範圍在25毫安培至100毫安培間幾乎是固定不動的。這顯示QCSE在奈米柱發光二極體元件上是被控制住的。此外，由拉曼頻譜分析及單晶X光繞射分析，我們可鑑別出，在此奈米結構中原本的晶格不匹配層會有一應力釋放的機制。

關鍵字

氮化鎵 ； 奈米柱 ； 發光二極體 ； 奈米粒子小球 ； 應力釋放

並列摘要

Since p-type GaN is well developed in 1990's, GaN has been widely useded in short wavelength light emitting diodes. Light emitting diodes have advantages such as low power consumption, long life time, good reliability, short response time. Nevertheless, there are still some spaces to improve it like quantum efficiency, peak wavelength shift.
A practical approach to fabricate textured GaN-based light emitting diodes (LEDs) by nanosphere lithography is presented. Due to the refraction index difference between GaN and air, there will be a total reflection at this interface and low external quantum efficiency. The current resolution is growing a rough p-type layer on conventional light emitting diodes to reduce the total reflection, but it needs extra time and more cost to do it. By spin-coating a monolayer of SiO2 nanoparticles as the mask, textured LEDs can be fabricated. Both textured p-GaN and textured ITO LEDs show significant improvement over the conventional LEDs without damaging the electric characteristics. The results show that the method is promising for low-cost manufacturing high efficient GaN-based LEDs.
The solution for peak wavelength shift is usually treated by growth some nanostructure to release the strain in material. We further use this practical process to fabricate InGaN/GaN multiple quantum well (MQW) LEDs with a self-organized nanorod structure is demonstrated. Contrary to epitaxy, we provide a novel way in fabrication process to solve the peak wavelength shift. Also, because of the hardness of parallel metal evaporation on tips of nanorods without short circuit, there are only a few related results. The nanorod array is realized by using nature lithography of surface patterned silica spheres followed by dry etching. A layer of spin-on-glass (SOG), which intervening the rod spacing, serves the purpose of electric isolation to each of the parallel nanorod LED units. The electroluminescence (EL) peak wavelengths of the nanorod LEDs nearly remain as constant for an injection current level between 25mA and 100mA, which indicates that the quantum confined stark effect (QCSE) suppressed in the nanorod devices. Furthermore, from the Raman light scattering and x ray diffraction analysis we identify a strain relaxation mechanism for lattice mismatch layers in the nanostructure.

並列關鍵字

GaN ； nanorod ； LED ； nanoparticles ； strain relaxation

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