Vertical illumination InAlAs avalanche photodiode for 50-Gbit/s applications

We achieved a high-performance InAlAs avalanche photodiode (APD) for beyond 25-Gbit/s applications, such as 50-Gbit/s. The large optical tolerance of the APD's vertical-illumination structure makes optical coupling easy compared with waveguide-type structures. The fabricated APD exhibits responsivity of 0.69 A/W with a large 3-dB bandwidth of 30 GHz at a multiplication factor (M) of 4.6, which enables 50-Gbit/s highly sensitive operation.