# Defect recombination origin of low energy excess in semiconductor detectors

**Authors:** Kai Nordlund, Fanhao Kong, Flyura Djurabekova, Matti Heikinheimo, Kimmo Tuominen, Nader Mirabolfathi  
**arXiv:** [2408.07518](https://arxiv.org/abs/2408.07518)  
**Date:** 2024-08-14  
**Summary page:** https://www.summarizepaper.com/en/paper/2408.07518v1/

## Key points

- Researchers investigate the phenomenon of an "excess" signal in semiconductor detectors at low energies
- Excess signal attributed to long-term recombination events of complex defects formed by nuclear recoil radiation events
- Recombination events exhibit exponential energy dependence and can trigger larger releases through avalanche effect
- Five-stage simulation and analysis procedure used to explore disordered damage zones and energy release on extended time scales
- Quantum thermal bath approach incorporated to evaluate quantum effects on annealing process

## Summary

In this study, the researchers investigate the phenomenon of an "excess" signal observed in semiconductor detectors when the detection threshold is pushed to low energies. This , consisting of apparent energy release events below a few hundred eV, poses a challenge to the sensitivity of these  for detecting rare event signals in this energy range. Through  utilizing classical thermostat and quantum thermal bath approaches, the researchers demonstrate that this  can be attributed to long-term recombination events of complex defects formed by nuclear recoil radiation events. The team's findings reveal that these recombination events exhibit an exponential dependence on energy similar to that observed in experiments. By conducting a detailed analysis of these recombination events, they uncover that crossing a low energy barrier (less than or equal to 0.1 eV) can trigger larger energy releases in an avalanche-like effect. This mechanism explains why large energy release events can occur even at . To further explore the production of disordered damage zones and potential energy release on extended time scales, the researchers employ a five-stage simulation and analysis procedure. This includes simulating radiation damage creation, thermal annealing of this damage over long periods, quenching configurations to 0 K to isolate potential energy release effects, extracting energy release data from recombination events, and analyzing the time scale of annealing. Additionally, considering quantum mechanical zero point vibrations at  may influence atom dynamics, the team incorporates a quantum thermal bath (QTB) into their simulations to evaluate how quantum effects impact the annealing process. Overall, this comprehensive investigation sheds light on the underlying mechanisms behind the low-energy  in  and provides valuable insights into understanding complex defect recombination processes in these systems.