为提升LED芯片的光提取效率和电流扩展能力, 设计了双金属层环形叉指结构ITO/DBR电极的大功率倒装LED芯片, 并对分布式布拉格反射镜(DBR)薄膜和环形叉指电极结构进行了仿真优化计算。利用TFcalc软件仿真计算了DBR堆栈方式、堆栈周期和参考波长对DBR反射率的影响。仿真结果表明, 优化设计的双堆栈DBR薄膜在234nm宽波长范围内反射率均高于95%, 对应蓝黄光区域(440~610nm)平均反射率高达98.95%, 参考波长红移可以缓解DBR反射偏振效应。利用SimuLED软件仿真计算了电极结构对芯片电流扩展能力的影响。仿真结果表明, 350mA电流输入情况下, 单金属层电极电流密度均方差为44.36A/cm2, 而双金属层环形叉指数目为3×3时, 电流密度均方差降至14.37A/cm2。双金属层环形叉指电极降低了p、n电极间距, 减小了电流流动路径, 芯片电流扩展性能明显提升。

To improve the light extraction efficiency and current spreading characteristic of LED chips, a novel kind of high power flip-chip LEDs with annular finger-like two-level metallization ITO/DBR electrode was presented, and the distributed Bragg reflectors (DBR) film and geometric topology of the electrodes were optimized by simulations. The influence of DBR stack mode, stack period and reference wavelength on DBR reflectivity was simulated with TFcalc software. The results show the reflectance of optimized DBR is higher than 95% over 234nm wavelength bandwidth, and the average reflectivity is higher than 98.95% in the wavelength range of 440~610nm. The influence of electrodes geometric topology on current spreading characteristic was also studied by SimuLED. The results show the standard deviation of current density is decreased from 44.36 to 14.37A/cm2 at 350mA for the high power flip-chip LEDs with 3×3 annular finger-like two-level metallization electrode. Annular finger-like two-level metallization electrode for flip-chip LEDs reduces the space between p and n electrodes, and shortens the current flow path, leading to a more favorable uniformity of current spreading.