# Influence of radiation damage on the absorption of near-infrared light in silicon

## TL;DR

This study measures how radiation damage from proton irradiation shortens the absorption length of near-infrared light in silicon, affecting its optical properties and band-gap.

## Contribution

It provides a phenomenological model describing the radiation-induced change in silicon's absorption length as a function of wavelength and fluence.

## Key findings

- Absorption length decreases with increased radiation fluence.
- Phenomenological parametrisation of absorption length change.
- Radiation-induced defects alter silicon's optical properties.

## Abstract

The absorption length, $\lambda_{abs}$, of light with wavelengths between 0.95 and 1.30$~\mu$m in silicon irradiated with 24$~$GeV/c protons to 1$~$MeV neutron equivalent fluences between 0 and $8.6 \times 10^{15}~$cm$^{-2}$ has been measured. It is found that $\lambda_{abs}$ decreases with fluence due to radiation-induced defects. A phenomenological parametrisation of the radiation-induced change of $\lambda_{abs}$ as a function of wavelength and neutron equivalent fluence at room temperature is given. The observation of the decrease of $\lambda_{abs}$ with irradiation is confirmed by edge-TCT measurements on irradiated silicon strip detectors. Using the measured wavelength dependence of $\lambda_{abs}$, the change of the silicon band-gap with fluence is determined.