High-performance germanium avalanche photodetector for 100  Gbit/s photonics receivers

Area of Science:

• Photonics
• Materials Science
• Electrical Engineering

Background:

• Waveguide-integrated photodetectors are crucial for optical interconnects.
• Germanium (Ge) is a key material for silicon photonics due to its compatibility with silicon CMOS technology.
• Achieving high-speed and high-gain photodetection at low bias voltages remains a challenge.

Purpose of the Study:

• To report a waveguide-integrated vertical germanium avalanche photodetector with optimized doping.
• To demonstrate high-bit rate and low-bias voltage operation.
• To enable energy-efficient silicon photonic interconnects.

Main Methods:

• Doping optimization of the germanium layer for simultaneous optical absorption and avalanche gain.
• Fabrication of a waveguide-integrated vertical germanium avalanche photodetector.
• Characterization of photodetector performance, including gain, gain-bandwidth product, and sensitivity at various bit rates.

Main Results:

• Maximum avalanche gain of 112.4 achieved at -30.2 dBm input power.
• Gain-bandwidth product of 141 GHz obtained at 7.8 V bias and -16.1 dBm input power.
• 4.6 dB sensitivity improvement for 60 Gbit/s signal reception with an avalanche gain of 5.1 at the soft-decision forward-error correction (SD-FEC) threshold.
• Absolute sensitivities of -21, -18.6, -15.9, and -11.5 dBm demonstrated for 40, 60, 80, and 100 Gbit/s non-return-to-zero signals, respectively.

Conclusions:

• The doping optimization scheme alleviates the need for complex epitaxial silicon layers and multiple ion implantations.
• The demonstrated device characteristics are suitable for reliable and robust on-chip photodetection.
• This work contributes to the development of energy-efficient silicon photonic interconnects.