Down-Scaling of GaN-Based Laser Diodes for High-Speed Modulation Characteristics

Recently, the surging need for greater bandwidth in the post-5G and 6G eras has prompted scientists to research visible light communications (VLC). VLC not only addresses the foreseeable limited radio frequency (RF) spectrum resources but also serves as a reliable solution for underwater wireless optical communication (UWOC). For high-speed VLC systems, GaN-based laser diodes have shown excellent potential over LEDs as emitting components. Downscaling laser diodes is considered an effective approach for high modulation bandwidth LDs, which has yet to be well studied in III-nitride material systems. In this work, we studied the key device design parameters, including cavity length, quantum well thickness, ridge waveguide width, and PN-junction distance. We analyzed the internal parameters of such high-speed InGaN/GaN double quantum well LDs and experimentally investigated their impact on the modulation bandwidth of LDs. As a result, a modulation bandwidth of 4.47 GHz (−3 dB) has been achieved. Our work provides valuable guidance for subsequent high-speed laser designs, paving the path for energy-efficient VLC systems.