Enhancing Light Extraction Efficiency of Vertical Emission of AlGaN Nanowire Light Emitting Diodes With Photonic Crystal
Enhancing Light Extraction Efficiency of Vertical Emission of AlGaN Nanowire Light Emitting Diodes With Photonic Crystal
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DOI：
10.1109/jphot.2019.2920517
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发表时间：
2019-06-01
影响因子：
2.4
通讯作者：
Cheng, Zhiyuan
中科院分区：
文献类型：
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作者：
Du, Pengwei;Cheng, Zhiyuan
AlGaN合金由于其能带隙覆盖200-360 nm波长范围而被广泛用于制作紫外发光二极管（UV-LED）。然而，AlGaN在深紫外范围内显示出强的横向磁极化，这严重阻碍了从UV-LED的顶表面的光提取。在本文中，我们提出了一种新的倒装芯片AlGaN纳米线发光二极管与顶部光子晶体，以提高光提取效率（LEE）从顶面的目的。利用三维时域有限差分法模拟纳米线发光二极管垂直方向的发光效率。通过仔细优化纳米线的尺寸和密度，我们证明了纳米线结构可以被设计成抑制导模的发射并促进从顶面的光提取。基于优化后的纳米线结构，我们还研究了顶部光子晶体对垂直发射LEE的影响。通过优化顶部光子晶体的高度、间距和半径，可以获得高达79.4%的高LEE。通过分析AlGaN纳米线发光二极管的横向电场分布，发现顶部光子晶体可以有效地将外延层中的光耦合到发光二极管外，从而提高垂直发射的LEE。
AlGaN alloys have been widely used to make ultraviolet light-emitting diodes (UV-LEDs) because its energy bandgap covers 200-360 nm wavelength range. However, AlGaN shows strong transverse magnetic polarization in deep UV range, which severely prevents light extraction from top surface of UV-LEDs. In this paper, we propose a novel flip-chip AlGaN nanowire LED with top photonic crystals, for the purpose of improving light extraction efficiency (LEE) from top surface. Using three-dimensional finite-difference time domain simulation, we first investigate the LEE in vertical direction of nanowire LEDs. By carefully optimizing the size and density of nanowires, we demonstrate that nanowire structures can be designed to inhibit the emission of guided mode and promote light extraction from top surface. Based on the optimized nanowire structure, we also study the effect of top photonic crystals on the LEE of vertical emission. A high LEE up to 79.4% can be achieved by optimizing the height, spacing, and radius of top photonic crystals. Analyzing the lateral electric field distribution of AlGaN nanowire LEDs with and without top photonic crystals, we find that top photonic crystals can effectively improve the LEE of vertical emission by coupling the light trapped in epitaxial layers out of LEDs.