Comparison of Beyond 1 GHz C-Plane Freestanding and Sapphire-Substrate GaN-Based micro-LEDs for High-Speed Visible Light Communication

With ever-growing demand for 6G networks technology, visible light communication (VLC) as a vital component of 6G has challenging requirement for superior performance of light source. Herein, 20 $\mu$ m blue micro-LED fabricated on 2-inch c -plane GaN freestanding substrate with high bandwidth over 1 GHz was first demonstrated, and the systematic comparisons to sapphire-substrate micro-LED from the epitaxial materials characterization to optoelectronic properties as well as communication performance were further conducted. GaN-substrate LED wafer has high crystal quality with lower threading dislocation density (TDD), which is two orders of magnitude lower than that of sapphire-substrate LED wafer. The much lower TDD of GaN-substrate LED wafer and better heat dissipation of GaN substrate offer GaN-substrate micro-LED great advantages in optoelectronic properties as well as communication performance. GaN-substrate micro-LED exhibited higher light output power (LOP) especially at high operating current, which is improved by $\sim$ 21% at 96 mA compared to that of sapphire substrate. Also, GaN-substrate micro-LED achieved a relatively higher bandwidth of 1.282 GHz while maintaining higher LOP with lower operating voltage. And a higher data rate of 4.48 Gbps under 1 m free space link was obtained by GaN-substrate micro-LED, proving it being a promising candidate in high-speed VLC.