Waveguided Ge/Si Avalanche Photodiode With Separate Vertical SEG-Ge Absorption, Lateral Si Charge, and Multiplication Configuration

A novel Si-waveguide-integrated Ge/Si avalanche photodiode (APD) is demonstrated for the first time, in which light propagating along the Si waveguide is evanescently absorbed by an overlaying Ge layer selectively grown on it, whereas the avalanche multiplication of photoexcited carriers occurs laterally in the Si-waveguide layer. The APD provides a responsivity of ~7.2 A/W at 1550 nm, which is ~26 times larger than the corresponding vertical Ge/Si p-i-n photodiode, and exhibits a 3-dB bandwidth of ~3.3 GHz, a dark current of ~22 ?A at 22-V bias, and an excess noise factor of ~4, respectively.