180 Gbit/s Si₃N₄-waveguide coupled germanium photodetector with improved quantum efficiency

Area of Science:

• Photonics and Optoelectronics
• Integrated Optics
• Semiconductor Devices

Background:

• Silicon photonics is a key technology for high-speed optical communication.
• Germanium-on-silicon (Ge-on-Si) photodetectors offer high performance but require efficient coupling.
• Silicon nitride (Si3N4) waveguides provide low loss and good mode confinement for integration.

Purpose of the Study:

• To develop a high quantum efficiency (QE) and high-speed Ge-on-Si photodetector (PD) integrated with a Si3N4 waveguide.
• To optimize device parameters for enhanced light absorption and efficient carrier collection.
• To demonstrate ultra-high data rate operation for next-generation optical networks.

Main Methods:

• Fabrication of a Ge-on-Si PD using a commercial 90 nm silicon photonics process.
• Optimization of Si3N4 waveguide dimensions (spacing to Si and thickness) for improved QE.
• Characterization of photodetector performance, including responsivity, bandwidth, and eye diagrams at various data rates.

Main Results:

• Achieved a maximum experimental responsivity of approximately 0.9 A/W at 1485 nm.
• Demonstrated a 3 dB optoelectrical bandwidth of up to 54 GHz at -3.3 V bias.
• Attained clear eye openings for non-return-to-zero on-off-keying up to 105 Gbit/s and four-level pulse amplitude modulation up to 180 Gbit/s.

Conclusions:

• The Si3N4-waveguide coupled Ge-on-Si PD exhibits significantly improved QE and operates at the highest data rates reported to date.
• The optimized device design enables high-performance optoelectronic conversion for advanced communication systems.
• This work highlights the potential of integrated silicon photonics for future high-capacity optical interconnects.