可见光通信中GaN-LED PN结面积对调制带宽的影响机理

在可见光无线通信中,用于照明的LED光源的调制带宽很低,只有几MHz,限制了基于LED光源的可见光通信的信息传输容量和速度。为构建高带宽LED,研究影响LED调制带宽的因素和机制。设计3组PN结面积分别为200μm×800μm,300μm×900μm和300μm×1200μm的LED芯片并倒装封装成LED器件,测试这3组器件的光电特性和调制带宽,并比较3组样品的电容曲线,分析调制带宽的主要影响因素之一——电容对LED器件的影响机制。实验结果表明PN结面积为200μm×800μm的LED器件具有最小电容,且具有最高的49.9 MHz的-3 dB调制带宽。由于封装、测试电路等引起寄生电容对LED器件调制带宽有重要影响,通过优化器件倒装结构、LED驱动电路等方法可以大幅度减少测试系统的寄生电容,提高LED器件的调制带宽。

Influence mechanism of GaN-LED's PN junction area on modulation bandwidth in visible light communication

Commercial Light-Emitting Diodes(LEDs)exhibit a-3 dB modulation bandwidth of only several MHz,which severely affects the information capacity and transmission in visible light communication.In this study,to fabricate an LED with high bandwidth,the influencing factors and mechanism of the modulation bandwidth of an LED device were investigated.Three LED chips with PN junction areas of 200μm×800μm,300μm×900μm,and 300μm×1200μm were designed and fabricated.By analyzing the photoelectric and modulation characteristics of the three LEDs,the relationship between the PN junction area and the modulation bandwidth was determined.Then,the capacitance-voltage curves of the three samples were compared,and the influence of the capacitance on the modulation bandwidth was analyzed.The results indicate that the LED with a PN junction area of 200μm×800μm exhibits the minimum capacitance,resulting in the maximum-3 dB bandwidth of 49.9 MHz among the three LEDs.This demonstrates that the parasitic capacitance caused by package,LED drive circuits,etc.,has a significant effect on the modulation bandwidth of LEDs.Thus,LED devices with high bandwidth can be fabricated by decreasing the parasitic capacitance of the LED.