GaN-Based Freestanding Micro-LEDs With GHz Bandwidth and Low Efficiency Droop for Visible Light Communication

Visible light communication (VLC) based on micro light-emitting diodes (micro-LEDs) offers energy-efficient methods for explosive data transmission. However, the severe quantum-confined stark effect (QCSE) and carrier localization make it challenging for micro-LEDs to achieve both high modulation bandwidth and high external quantum efficiency (EQE). Herein, GaN-based freestanding micro-LEDs with varying quantum barrier (QB) thicknesses were designed and fabricated. The thinner QBs effectively reduce the QCSE and improve carrier transport, resulting in high modulation bandwidth and less efficiency droop. Homoepitaxial growth of micro-LEDs gives birth to further improved modulation bandwidth and optical power due to lower defect density and improved thermal dispassion. The −3 dB bandwidths of the 10 and $20~\mu $ m-diameter freestanding micro-LEDs exceed 1.03 GHz and 823 MHz, respectively. A high optical power of 5.54 mW and a data rate of 4.08 Gb/s, while maintaining a relatively high EQE of 4.17%, were achieved on $20~\mu $ m-diameter devices. The proposed methods systematically improve the modulation bandwidth and luminescence efficiency, demonstrating the significant potential for free-space VLC.