GaN-Based Laser Diode with a Trapezoidal EBL and an Unintentionally Doped Layer Reaching 7.8 GHz Modulation Bandwidth

Laser-based visible light communication (VLC) has emerged as a rapidly growing technology for underwater wireless optical communication, industrial IoT network, optical interconnection, and other important applications. The development of a high-speed GaN-based laser transmitter becomes critical for VLC links with the increasing demand for data transmission rates. There exists electron leakage and a low differential gain in InGaN quantum well (QW) laser diodes (LDs), limiting their frequency response. In this work, we have studied the impact of structural design and parameters on the modulation bandwidth of blue LDs. A new structure design with a trapezoidal electron blocking layer (EBL) and an unintentionally doped layer adjacent to the QWs was proposed to address those challenges. The fabricated 2 μm ridge waveguide LDs exhibit a relatively low threshold current of 17 mA and a high slope efficiency of 1.6 W/A. A large modulation bandwidth of 7.8 GHz has been measured from 500 μm long cavity LDs, which is a record value in GaN-based LDs, to the best of our knowledge. The LDs show a small damping factor of 0.26 ns while maintaining a wall-plug efficiency exceeding 25%. The work presents a large bandwidth device for visible light transmitters, paving the way for the realization of high-speed laser-based VLC links.