High-Speed GaN-Based Blue Light-Emitting Diodes With Gallium-Doped ZnO Current Spreading Layer

Conventional light-emitting diodes (LEDs) always pursue the high brightness required for solid-state lighting. However, they always exhibit very low frequency bandwidth of tens MHz. In this letter, we investigate the fabrication and characterization of high-speed GaN-based blue LEDs. The frequency response of LEDs is mainly limited by its diffusion capacitance and resistance, and the injected carriers in the active region of the device. Through appropriate device design, gallium-doped Zinc oxide film deposited by atomic layer deposition is used as the top contact layer with high lateral resistance to self-confine the current injection. In addition, a smaller bonding pad is used to reduce the RC time constant. Thus, the GaN-based blue LEDs with a 75-μm diameter exhibit a 3-dB modulation bandwidth of 225.4 MHz and a light output power of 1.6 mW at the current of 35 mA. Such LEDs can be applied to visible light communication in future.