# Study of Neutron-, Proton-, and Gamma-Irradiated Silicon Detectors Using the Two-Photon Absorption–Transient Current Technique

## TL;DR

This paper studies how neutron, proton, and gamma irradiation affect silicon detectors using a technique that tracks charge movement with laser light.

## Contribution

The study reveals irradiation-induced linear absorption and electric field inversion in proton-irradiated silicon detectors.

## Key findings

- Neutron and proton irradiation cause additional linear absorption not seen in gamma-irradiated detectors.
- The absorption is linked to cluster damage and scales with non-ionising energy loss.
- Proton-irradiated detectors show an inverted electric field compared to neutron-irradiated ones at high fluence.

## Abstract

The Two-Photon Absorption–Transient Current Technique (TPA-TCT) is a device characterisation technique that enables three-dimensional spatial resolution. Laser light in the quadratic absorption regime is employed to generate excess charge carriers only in a small volume around the focal spot. The drift of the excess charge carriers is studied to obtain information about the device under test. Neutron-, proton-, and gamma-irradiated p-type pad silicon detectors up to equivalent fluences of about 7 × 1015 neq/cm2 and a dose of 186 Mrad are investigated to study irradiation-induced effects on the TPA-TCT. Neutron and proton irradiation lead to additional linear absorption, which does not occur in gamma-irradiated detectors. The additional absorption is related to cluster damage, and the absorption scales according to the non-ionising energy loss. The influence of irradiation on the two-photon absorption coefficient is investigated, as well as potential laser beam depletion by the irradiation-induced linear absorption. Further, the electric field in neutron- and proton-irradiated pad detectors at an equivalent fluence of about 7 × 1015 neq/cm2 is investigated, where the space charge of the proton-irradiated devices appears inverted compared to the neutron-irradiated device.