High-speed waveguide-integrated Ge/Si avalanche photodetector

Waveguide-integrated Ge/Si heterostructure avalanche photodetectors (APDs) were designed and fabricated using a CMOS-compatible process on 8-inch SOI substrate. The structure of the APD was designed as separate-absorption-charge-multiplication (SACM) using germanium and silicon as absorption region and multiplication region, respectively. The breakdown voltage (V_b) of such a device is 19 V at reverse bias and dark current appears to be 0.71 μA at 90% of the V_b. The device with a 10-μ length and 7-μ width of Ge layer shows a maximum 3-dB bandwidth of 17.8 GHz at the wavelength of 1550 nm. For the device with a 30-μ-length Ge region, gain-bandwidth product achieves 325 GHz.