Lattice vibrations of point defects are essential for understanding nonradiative electron and hole capture in semiconductors as they govern properties including persistent photoconductivity and the 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 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 tunneling 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.
Bibliographical noteFunding Information:
Acknowledgments. We thank Lucy D. Whalley and Ji-Sang Park for valuable discussions, and Audrius Alkauskas for helpful comments on our manuscript. This work was supported by the EU Horizon2020 Framework (STARCELL, Grant No. 720907). Additional funds were received from the Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (2018M3D1A1058536). Via our membership of the UK's HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), this work used the ARCHER U.K. National Supercomputing Service  .
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics