AlGaN基深紫外Micro-LED的光提取效率模拟研究

AlGaN基深紫外Micro-LED在固化、灭菌、可见光通信、显示技术等领域有广泛的用途。但是目前深紫外Micro-LED在效率方面面临着重大挑战，由于GaN对深紫外光强烈的吸收，外延层与空气之间的全内反射以及独特的横磁场（Transverse Magnetic, TM）光偏振现象，使得光提取效率极低，这也导致了外量子效率很低。因此，提升光提取效率对实现高效深紫外Micro-LED具有重大意义。本文通过数值模拟的方法，系统地对光提取效率的尺寸效应进行了探究，并进一步优化台面结构提升了倒装深紫外Micro-LED的光提取效率。

Micro-LED的效率与尺寸有着紧密的联系，但目前关于深紫外Micro-LED光提取效率的尺寸效应研究极少。为此，本文系统地探究了100 μm以内深紫外Micro-LED光提取效率的尺寸效应。研究结果表明，由于TM偏振光具有横向传播的性质，小尺寸的Micro-LED能够让更多的TM偏振光在侧壁射出空气，所以深紫外Micro-LED光提取效率随着尺寸的减小而增大。以上结果揭示了更高的光提取效率是造成更小尺寸的深紫外Micro-LED外量子效率更高的主要原因，这为AlGaN基深紫外Micro-LED效率的尺寸效应研究提供了数据支撑。

针对倒装结构的Micro-LED，本文通过优化台面结构来增强光提取效率。首先针对横电场（Transverse Electric, TE）偏振光垂直于外延层传播的特性和电极的反射作用，根据干涉效应优化了p-AlGaN和p-GaN的厚度，将TE偏振模式下的光提取效率提升了近两倍。进一步地，针对TM偏振光横向传播的特性，探究侧壁倾角对光提取效率的影响，结果表明最优倾角为40°。通过两方面的优化，最终实现了总的光提取效率提升123%，这对提升深紫外Micro-LED的效率提供了器件结构方面的设计思路。

综合而言，本研究系统地探究了AlGaN基深紫外Micro-LED光提取效率的尺寸效应，并通过优化台面结构提高了倒装Micro-LED的光提取效率。这对于实现高效的AlGaN基深紫外Micro-LED具有重要意义，为相关领域的应用和进一步研究提供了有价值的数据支持。

AlGaN-based deep ultraviolet Micro-LEDs have found widespread applications in curing, sterilization, visible light communication, and display technologies. However, significant challenges persist in enhancing the efficiency of Micro-LEDs. The strong absorption of deep ultraviolet light by GaN, total internal reflection between the epitaxial layer and air, and the unique Transverse Magnetic (TM) light polarization phenomenon lead to extremely low light extraction efficiency, subsequently resulting in low external quantum efficiency. Therefore, improving light extraction efficiency holds significant importance for achieving highly efficient deep ultraviolet Micro-LEDs. This thesis systematically investigates the size-dependence on light extraction efficiency through numerical simulations and further optimizes the mesa structure to enhance the light extraction efficiency of flip-chip deep ultraviolet Micro-LEDs.

The efficiency of Micro-LEDs is closely related to the size, but there are currently very few studies on the size-dependence on light extraction efficiency of deep ultraviolet Micro-LEDs. This study systematically explores the size-dependence on light extraction efficiency of deep ultraviolet Micro-LEDs within 100 μm. The results reveal that due to the transverse propagation property of TM-polarized light, smaller-sized Micro-LEDs allow more TM-polarized light to escape through the sidewall into the air. Consequently, the light extraction efficiency of deep ultraviolet Micro-LEDs increases as their size decreases. These findings highlight that higher light extraction efficiency is the main reason for achieving higher external quantum efficiency in smaller-sized deep ultraviolet Micro-LEDs, providing valuable data support for the study of size-dependence on the efficiency of AlGaN-based deep ultraviolet Micro-LEDs.

For flip-chip Micro-LEDs, this study focuses on optimizing the mesa structure to enhance light extraction efficiency. First, targeting the vertical propagation property of Transverse Electric (TE) polarized light and the reflection from the electrodes, the thicknesses of p-AlGaN and p-GaN layers are optimized using interference effect, resulting in nearly double the light extraction efficiency in the TE polarization mode. Furthermore, considering the transverse propagation property of TM-polarized light, the influence of sidewall inclination angle on light extraction efficiency is investigated, and the optimal inclination angle is determined to be 40°. Through these two optimization approaches, the overall light extraction efficiency improvement of 123% is achieved, providing valuable design insights for enhancing the efficiency of deep ultraviolet Micro-LEDs.

In summary, this study reveals the size-dependence on light extraction efficiency in AlGaN-based deep ultraviolet Micro-LEDs， and optimizes the mesa structure to improve the light extraction efficiency of flip-chip Micro-LEDs. These findings are significant for achieving highly efficient AlGaN-based deep ultraviolet Micro-LEDs and provide valuable data support for applications and further research in related fields.

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