利用有限时域差分法研究近紫外垂直结构LED的光萃取效率的影响因素。结果显示, LED的光萃取效率随p-GaN层厚度的变化呈周期性振荡变化, 在极大值点处的光萃取效率是极小值点处的4.8倍。进一步地, 对上述振荡极大值点和极小值点的n-GaN层厚度和表面光子晶体结构进行优化,优化的光萃取效率分别达到35.3%和24.7%, 比优化前各提高了37.9%和280%。因此, 合理的外延层和光子晶体结构可有效提高近紫外垂直结构LED的光萃取效率, 这对实验制备高效近紫外垂直结构LED芯片具有一定的指导作用。

Optimization of LED epilayer and photonic crystals (PC) structure for high light extraction efficiency (LEE) UV-A vertical-structure LEDs (VS-LEDs) were performed by using finite difference time domain method. The LEE of the VS-LEDs was markedly enhanced by optimizing the thicknesses of p-GaN layer and parameters of PC structure. The LEE of the VS-LEDs shows cyclic variation as function of the thicknesses of p-GaN layer. It is showed that the LEE of the VS-LEDs with the p-GaN thickness of 200 nm is 4.8 times to that of the VS-LEDs with the p-GaN thickness of 310 nm. In addition, the thickness of the n-GaN layer and the surface photonic crystal structure were further optimized, and the LEE of the VS-LEDs with the p-GaN thickness of 200 nm and 310 nm reaches 35.3% and 24.7%, respectively. The optimized LEE of the VS-LEDs is 1.4 and 3.8 times to that of the VS-LEDs without PC structure, respectively. Therefore, the reasonable LED epilayer and the PC structure can effectively improve the LEE of the VS-LEDs. It provides a theoretical guide for the preparation of the UV-A VS-LEDs.