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, galliumdoped 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.

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In this letter, we investigate the fabrication and characterization of high-speed GaAs-based near-infrared (near-IR) light-emitting diodes (LEDs) by using gallium-doped zinc oxide (GZO) as the current-spreading layer. For the GZO contacts to p + -type GaAs prepared by atomic layer deposition, the minimum specific contact resistance of 1.7 × 10 −5 -cm 2 is obtained. The GaAs-based near-IR LEDs with an aperture diameter of 59 μm and a smaller bonding pad of 80 μm have a low forward voltage of 1.7 V at 20 mA, a series resistance of 5.6 , the total capacitance of 17.5 pF, and a light output power of 4.6 mW at 50 mA. By the design of a ring-shaped electrode overlapping with GZO film, the LED exhibits a 3-dB modulation bandwidth of 107.8 MHz at a driving current of 50 mA owing to the increase of injected current density into the confined region.

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