采用银纳米圆盘阵列提高LED发光特性的研究

为了提高GaN基蓝光LED的发光效率,设计了在LED有源层上方引入银纳米圆盘阵列的模型。利用时域有限差分方法计算了银纳米圆盘阵列不同结构参数情况下LED有源层自发辐射率的变化情况及光提取效率值。通过对有源区的近场分布和LED远场方向性的分析,理论上解释了利用该金属纳米结构生成的表面等离激元对LED性能增强的影响,利用该模型可使得表面等离激元与有源层有效耦合,从而增强有源层的自发辐射率。此外,银纳米粒子组成的阵列结构所生成的栅格矢量可以补偿表面等离激元的波矢量,从而可将局域化表面等离激元转为辐射性表面等离激元,显著提高LED顶端光提取效率。结果表明,当银纳米圆盘颗粒满足直径为120nm,厚度为30nm时,含该结构的GaN基蓝光LED自发辐射率比普通LED增强了3.6倍。在此基础上,当其按照晶格常数为220nm的三角晶格排列时,顶端光提取效率增强为2.5倍。这些结果为实际的高性能GaN基LED的设计与优化提供了一定的参考。

Study on Improving Light Emitting Efficiency of LED by Using Silver Nanodisk Array

In order to improve the light emitting efficiency of GaN-based blue LED, a novel LED model, which has a layer of silver nanodisk array embedded above the quantum well, is designed. The rates of spontaneous emission change and light extraction efficiencies of the models with various geometric parameters are calculated by using finite-difference time-domain method. With the analysis for near field distribution of active region (AR) and far field directivity of LED, we theoretically explain the influence of surface plasmon polaritons (SPP) formed on silver nanodisks on the improvement of LED performance. This model could contribute to the coupling between SPP and AR, leading to the enhancement of spontaneous emission of AR. Besides, due to the compensation for wave vector of SPP by lattice vector of silver nanodisk array, the localized SPP could radiate to space and light extraction efficiency of LED could be improved. Optimization results show that on the condition that the diameter of nanodisk is set to 120 nm and its thickness is chosen as 30 nm, the spontaneous emission is enhanced by 3.6 times compared to that of the conventional LED. Furthermore, as the nanodisks are arranged to the array with triangular lattice and the lattice constant is 220 nm, light extraction efficiency gets 2.5 times enhancement. These results provide a theoretical reference on the practical design and optimization of highly efficient GaN-based LED.