Charge state and hydration of vacancies in silicon and silicon carbide in contact with water: A grand-canonical first-principles stability map
Abstract
The state of a vacancy in a semiconductor is normally described by the Fermi level alone. In wet-etched, electrochemically processed, or humid silicon and silicon carbide, a vacancy also takes up hydrogen and oxygen from water, in amounts set by pH and electrode potential. We treat both effects together by minimizing the grand potential of a vacancy complex over its charge state and hydrogen/oxygen content. The result is a stability map in Fermi level and hydrogen chemical potential, which the computational hydrogen electrode relates to pH and potential. We parameterize it with spin-polarized density functional theory in 64-atom cells, including the vibrational free energy of bound H and O, for the silicon vacancy, its H, O, and OH complexes, and both vacancies of 3C-SiC. Hydrogen binds cooperatively to the silicon vacancy, which goes directly from bare to fully passivated VH4. In contact with water the bare vacancy is never the lowest-energy state. Near neutral pH it binds oxygen from water as the A center, the paramagnetic hydroxyl complex forms below about pH 5 at zero bias, and full passivation to VH4 requires cathodic bias. In PBE the Fermi level barely moves these boundaries, because the acceptor levels lie at or above the conduction-band edge. In SiC the first hydrogen binds to the silicon vacancy by 1.97 eV but is unbound at the carbon vacancy (the Z1/2 center), so hydrogen from water alone should not passivate it except under cathodic bias.
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BibTeX
@misc{patra2026charge,
title = {{Charge state and hydration of vacancies in silicon and silicon carbide in contact with water: A grand-canonical first-principles stability map}},
author = {Abhirup Patra},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.33469},
eprint = {2610.33469},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.33469},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Charge state and hydration of vacancies in silicon and silicon carbide in contact with water: A grand-canonical first-principles stability map
AU - Abhirup Patra
PY - 2026
DA - 2026/10/24
PB - arXiv
DO - 10.48550/arxiv.2610.33469
UR - https://arxiv.org/abs/2610.33469
AB - The state of a vacancy in a semiconductor is normally described by the Fermi level alone. In wet-etched, electrochemically processed, or humid silicon and silicon carbide, a vacancy also takes up hydrogen and oxygen from water, in amounts set by pH and electrode potential. We treat both effects together by minimizing the grand potential of a vacancy complex over its charge state and hydrogen/oxygen content. The result is a stability map in Fermi level and hydrogen chemical potential, which the computational hydrogen electrode relates to pH and potential. We parameterize it with spin-polarized density functional theory in 64-atom cells, including the vibrational free energy of bound H and O, for the silicon vacancy, its H, O, and OH complexes, and both vacancies of 3C-SiC. Hydrogen binds cooperatively to the silicon vacancy, which goes directly from bare to fully passivated VH_4. In contact with water the bare vacancy is never the lowest-energy state. Near neutral pH it binds oxygen from water as the A center, the paramagnetic hydroxyl complex forms below about pH 5 at zero bias, and full passivation to VH_4 requires cathodic bias. In PBE the Fermi level barely moves these boundaries, because the acceptor levels lie at or above the conduction-band edge. In SiC the first hydrogen binds to the silicon vacancy by 1.97 eV but is unbound at the carbon vacancy (the Z_1/2 center), so hydrogen from water alone should not passivate it except under cathodic bias.
ER -