藉表面電漿子耦合以減輕發光二極體效率滑落之數值研究

Numerical Study on Mitigating Efficiency Droop of a Light-Emitting Diode through Surface Plasmon Coupling

陳建志(Chien-Chih Chen)

指導教授 ： 江衍偉

共同指導教授 ： 楊志忠

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201702464

摘要

本論文中，我們利用數值模擬方法探討發光二極體透過表面電漿子與量子井耦合以減輕發光效率滑落。當設計一金屬奈米結構於量子井附近，量子井發光入射到金屬奈米結構上產生表面電漿子並與量子井耦合，可以藉由Purcell效應增強量子井自發輻射率。我們修改原本描述量子井內載子濃度變率方程式的ABC模型，使其包含了Purcell效應和金屬結構的吸收，並進一步推導電流成分、載子濃度、載子生命期和注入效率等公式。
我們設計一金屬奈米結構，將特定大小的銀奈米粒子置於p型氮化鎵上方，調整p型氮化鎵的厚度以及振盪電偶極與銀粒子的水平距離，計算不同情況下的Purcell因子和金屬吸收參數。假設適當的內部量子效率極大值和相對應的量子井電流，將上述計算結果代入修改後的ABC模型，即可得有表面電漿子耦合的內部量子效率、注入效率、載子濃度和電流成分等。數值結果顯示，當有表面電漿子耦合時，可增強載子輻射復合率和載子注入效率，降低量子井內的載子濃度和Auger復合，因此藍光和綠光的發光二極體皆可透過表面電漿子耦合而增強發光效率且改善效率滑落。

關鍵字

發光二極體 ； 效率滑落 ； 表面電漿子 ； Purcell效應

並列摘要

In this thesis, mitigating efficiency droop of a light-emitting diode (LED) through the coupling between a quantum well (QW) and a surface plasmon (SP) resonance is numerically investigated. With a metal nanostructure near a QW, through SP coupling the radiative recombination rate in the QW can be increased due to the Purcell effect. We modify the carrier-density rate equation of the so-called “ABC” model to include the Purcell effect as well as the absorption in the metal nanostructure. Furthermore, we derive the formulas for various current components, carrier density, carrier lifetime and injection efficiency.
With a properly designed metal nanostructure, an Ag nanoparticle is placed on the top surface of a thick GaN layer with an embedded thin QW layer. By varying the vertical and horizontal separations between a radiating dipole and the Ag nanoparticle, we calculate the Purcell factor and the absorption factor under various situations. With these numerical data as well as assumed maximum internal quantum efficiency (IQE) and the corresponding QW injection current of a reference LED, we can evaluate the IQE, injection efficiency, carrier density and current components of an SP-coupled LED. Numerical results show that SP coupling can enhance the radiative recombination rate and the injection efficiency. At the same time, both the carrier density in the QW and Auger recombination rate are reduced. As a result, the emission efficiency of either blue or green LEDs can be enhanced and efficiency droop mitigated through SP coupling.

並列關鍵字

light-emitting diode ； efficiency droop ； surface plasmon ； Purcell effect

參考文獻

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