How fast can a light-emitting diode be modulated?

Beyond their traditional roles in lighting and display technologies, light-emitting diodes (LEDs) are increasingly recognized as cost-effective light sources for communication. While the modulation bandwidth of LEDs was once thought to be capped at around 100 MHz, recent advances have seen micro-scale LEDs (micro-LEDs) with bandwidths surpassing 1 GHz, driven by the demands of visible light communication applications. Emerging applications such as in-vehicle optical communication and chip-to-chip optical interconnection now require transmission speeds of 10 Gbps per channel under non-return-to-zero on-off keying (NRZ-OOK) modulation. In this context, the -3 dB bandwidth of micro-LEDs is anticipated to reach 7 GHz, significantly exceeding current capabilities. This paper systematically examines the factors that fundamentally limit the modulation bandwidth of micro-LEDs and discusses their impact as current density increases. We predict that the electrical-to-electrical (E-E) −3 dB bandwidth of quantum well (QW) micro-LEDs at room temperature will be less than 2 GHz. However, micro-LEDs featuring an InGaN quantum dot (QD) active region, due to their enhanced quantum confinement and carrier localization, have already achieved a maximum E-E −3 dB bandwidth of 3.6 GHz. Our theoretical predictions and equivalent circuit model analysis suggest that with optimizing the QD growth size, reducing the device size to less than 5 μm, and addressing the detector bandwidth limitation, this bandwidth could be measured to exceed 7 GHz. These findings pave the way for the future of high-speed, low-cost short-distance optical interconnection applications.