Linear Multiplication Beyond Geiger Mode Threshold in Ge-on-Si Avalanche Photodiode

Area of Science:

• Optoelectronics
• Semiconductor Physics
• Materials Science

Background:

• Germanium-on-silicon (Ge-on-Si) avalanche photodetectors (APDs) are crucial for optical communications.
• Understanding their operational modes, especially beyond standard avalanche breakdown, is essential for device optimization.

Purpose of the Study:

• To investigate the avalanche behavior of vertically structured Ge-on-Si APDs under ramp gating.
• To analyze the impact of interface and deep-level traps on device performance.
• To explore the device's response to short-wave infrared illumination.

Main Methods:

• Fabrication of a vertically structured Ge-on-Si APD in a separate absorption, charge, and multiplication configuration.
• Application of ramp gating to achieve bias beyond punch-through voltage.
• Characterization of dark current and response to pulsed 1550 nm illumination.

Main Results:

• Observed linear avalanche mode enabled by ramp gating, with dark current proportional to gating and thermal generation.
• Linear multiplication behavior persisted even beyond Geiger mode voltages.
• Negative differential resistance under illumination attributed to self-quenching and interface barrier modification.
• Light-induced transient current decrease followed by inverse quenching restoring dark current.

Conclusions:

• Ge/Si interface traps and fabrication-induced deep-level traps significantly influence Ge-on-Si APD behavior.
• The device exhibits unique dynamic responses, including linear avalanche mode and illumination-induced quenching effects.
• Findings provide critical insights for designing advanced Ge-on-Si photodetectors for optoelectronic applications.