High-Bandwidth and High-Responsivity Top-Illuminated Germanium Photodiodes for Optical Interconnection

In this paper, we report efficient high-speed top-illuminated p-i-n photodiodes with high responsivity fabricated from germanium (Ge) films grown directly on silicon-on-insulator substrates. The devices were characterized with respect to their dark current, responsivity, and 3-dB bandwidth (BW) in the near infrared. For a 20-μm-diameter device at room temperature, the dark current densities were approximately 38.3 mA/cm
²
at -1 V. The responsivity (\mmb
R
) at 1.55 μm was 0.30 A/W, corresponding to a quantum efficiency of 24%. The 3-dB BW of the detector with 20-μm diameter is as high as 23.3 GHz.