# Anharmonic Lattice Relaxation during Non-radiative Carrier Capture

## TL;DR

This paper develops a first-principles method to model anharmonic lattice relaxation in defect-related non-radiative carrier capture, successfully explaining experimental observations in GaAs that harmonic models cannot.

## Contribution

It introduces a novel approach to account for anharmonic effects in defect lattice vibrations, improving the accuracy of carrier capture predictions in semiconductors.

## Key findings

- Accurately predicts the electron capture barrier in GaAs DX centers.
- Shows the absence of quantum tunneling at low temperatures.
- Explains the composition-invariant electron emission barrier.

## Abstract

Lattice vibrations of point defects are essential for understanding non-radiative electron and hole capture in semiconductors as they govern properties including persistent photoconductivity and Shockley-Read-Hall recombination rate. Although the harmonic approximation is sufficient to describe a defect with small lattice relaxation, for cases of large lattice relaxation it is likely to break down. We describe a first-principles procedure to account for anharmonic carrier capture and apply it to the important case of the \textit{DX} center in GaAs. This is a system where the harmonic approximation grossly fails. Our treatment of the anharmonic Morse-like potentials accurately describes the observed electron capture barrier, predicting the absence of quantum tunnelling at low temperature, and a high hole capture rate that is independent of temperature. The model also explains the origin of the composition-invariant electron emission barrier. These results highlight an important shortcoming of the standard approach for describing point defect ionization that is accompanied by large lattice relaxation, where charge transfer occurs far from the equilibrium configuration.