纳米半球微镜阵列结构对GaN基LED光提取效率的影响

为了分析表面纳米半球微镜结构对GaN基发光二极管（LED)光提取效率的影响，利用时域有限差分法(FDTD)分别对GaN、ZnO、SiO2、聚苯乙烯组成的半球微镜结构进行了分析和比较，同时用模式分析方法从理论上对FDTD计算结果进行了进一步验证。研究发现，在亚波长范围，折射率较小的材料不利于导模与表面结构层的耦合，不会对光提取效率的提高产生明显影响。相比之下，折射率较大的材料会使更多的模式耦合到半球微镜阵列层，更有利于光提取效率的提高；当材料选定，纳米半球半径增加时，光提取效率也逐渐增加，优化后半径为600 nm的半球微镜阵列结构GaN基LED，其光提取效率比没有结构的普通平板LED增强5.66倍，在以上波导材料结构中最为优化。在此基础上，通过等效折射率的计算得到半球微镜结构的等效折射率模型，并利用非对称平板模式分析的办法对以上得到的结论进行了分析和验证。这些结果对实际的高性能GaN基LED的设计与优化具有重要意义。

Effect of Structure of Nano-Hemisphere Microlens Array on Light Extraction Efficiency of GaN-LED

To improve the light extraction efficiency (LEE) of GaN-LED with hemisphere microlens array surface structure, four kinds of waveguide materials such as GaN, ZnO, SiO2 and polystyrene are studied with finite-difference time-domain method. The simulation results are further tested by mode analysis method. The results show that the LEE can be improved when the refractive index grows higher, and the LEE of microlens array with bigger radius hemisphere is better in the subwavelength structure. The optimized model with 600 nm radius hemisphere microlens array of GaN material, with which the LEE exhibites 5.66 times enhancement than that of the planar LED, is the best output among those results. The above results are analyzed and verified by the asymmetric planar mode analysis method with equivalent refractive index. These results provide a theoretical guide on the practical design and optimization of highly efficient GaN-based LED.