III-Nitride-Based Cyan Light-Emitting Diodes With GHz Bandwidth for High-Speed Visible Light Communication

A large reduction (from 17 to 5 nm) is made in the thickness of the barrier layers in the multiple-quantum-well region of III-nitride-based cyan light-emitting diodes (LEDs) grown on patterned sapphire substrates. This is shown to lead to a simultaneous improvement in the modulation speed, differential quantum efficiency, and maximum output power of the LEDs under both room temperature and 110 degrees C operation. With our novel device structure, we achieve a moderate output power (1.7 mW) with a record high 3-dB electrical-to-optical (E-O) bandwidth (1 GHz). The over twofold enhancement in the E-O bandwidth (similar to 1 versus similar to 0.5 GHz) compared with that previously reported visible LEDs can be attributed to the more uniform distribution of injected carriers within the MQW region and the aggressive downscaling of the thickness of the total active layer, which leads to a shortening of the spontaneous recombination time.