# Laser annealing heals radiation damage in avalanche photodiodes

## TL;DR

High-power laser annealing effectively repairs radiation damage in avalanche photodiodes, significantly reducing dark count rates while preserving key detection characteristics, thus extending their operational lifetime in space-based quantum communication systems.

## Contribution

This study demonstrates that laser annealing can heal radiation damage in APDs, restoring performance and extending their lifespan in space applications, which was not previously established.

## Key findings

- Dark count rates reduced by up to 758 times at -80°C.
- Laser annealing does not significantly affect photon detection efficiency.
- The method is effective across multiple APD models.

## Abstract

Avalanche photodiodes (APDs) are a practical option for space-based quantum communications requiring single-photon detection. However, radiation damage to APDs significantly increases their dark count rates and reduces their useful lifetimes in orbit. We show that high-power laser annealing of irradiated APDs of three different models (Excelitas C30902SH, Excelitas SLiK, and Laser Components SAP500S2) heals the radiation damage and substantially restores low dark count rates. Of nine samples, the maximum dark count rate reduction factor varies between 5.3 and 758 when operating at minus 80 degrees Celsius. The illumination power to reach these reduction factors ranges from 0.8 to 1.6 W. Other photon detection characteristics, such as photon detection efficiency, timing jitter, and afterpulsing probability, remain mostly unaffected. These results herald a promising method to extend the lifetime of a quantum satellite equipped with APDs.