# The Frequency Response Characteristics of Ge-on-Si Photodetectors Under High Incident Power

## TL;DR

This paper investigates why germanium photodetectors lose performance at high light power and offers solutions to improve their design.

## Contribution

The study is the first to analyze the combined effects of carrier saturation and shielding on bandwidth reduction in Ge-on-Si photodetectors.

## Key findings

- Bandwidth is mainly affected by carrier saturation drift velocity below 2.5 mW incident power.
- At over 3 mW, both carrier saturation and shielding effects reduce bandwidth.
- Increasing bias voltage mitigates the carrier-shielding effect.

## Abstract

This study explores the mechanisms responsible for the bandwidth reduction observed in germanium photodetectors under high signal light power. We investigate the impact of the carrier-shielding effect on the bandwidth through simulations, and we mitigate this effect by increasing the applied bias voltage. The increase in the concentration of photogenerated carriers leads to a reduction in the carrier saturation drift velocity, which reduces the bandwidth of the germanium photodetector; this phenomenon is studied for the first time. The bandwidth is determined primarily by the carrier saturation drift velocity when the incident light power is below 2.5 mW. The decrease in bandwidth that is calculated based on the decrease in carrier saturation drift velocity is consistent with the experimental results. However, when the signal light power exceeds 3 mW, both the carrier-shielding effect and the reduction in the carrier saturation drift velocity contribute to the bandwidth reduction. This study provides good theoretical guidance for the design of high-power germanium photodetectors.