Bandwidth Analysis of High-Speed InGaN Micro-LEDs by an Equivalent Circuit Model

High-speed light-emitting diodes (LEDs) are ideal light sources for low-cost plastic optical fiber communication in data-centers and vehicles. Here, high-speed micro-LEDs based on InGaN quantum dot (QD) active region with different diameters are fabricated and characterized. The −3dB bandwidth around 3.6 GHz and 1.4 GHz are achieved in the blue and green micro-LEDs under current density less than 1 kA/cm2, respectively, which can work at an environmental temperature of 125 °C. An equivalent circuit model is proposed to analyze the limiting factors of the bandwidth, using which the effects of carrier recombination and RC time constant on modulation bandwidth are separated. It is found that carrier recombination rate is fast enough and the RC constant is still the main limiting factor for the blue micro-LEDs at an injection current density of more than 500 A/cm2 even when the diameter scales down to $20 \mu \text{m}$ , while the recombination rate mainly limits the bandwidth of the green micro-LEDs.