Influence of isovalent dopants on vacancy–oxygen–hydrogen defects in silicon

The vacancy–oxygen (VOi) center is an important defect in Si, introducing energy levels within the bandgap and acting as a recombination center that degrades device performance. Hydrogen can passivate the VOi center, forming defects such as VOiHi, which modify the electronic structure and produce characteristic infrared signatures. Controlling the electrical activity of these hydrogen-related complexes is, therefore, critical, and isovalent dopants such as C and Ge offer a potential route to tune their stability and behavior. Here, we employ density functional theory calculations to investigate the structural and electronic properties of VOiHi complexes under isovalent doping. It was found that C, being much smaller than Si, exhibits a positive binding energy, indicating that the CVOiHi complex is unstable despite strong covalent hybridization and the absence of mid-gap states. In contrast, Ge shows negative binding energies, signifying stable complex formation, with substitutional energies following a nonmonotonic trend influenced by both size mismatch and lattice relaxation. Density of states analysis further reveals that these heavier dopants introduce sharp dopant-derived p-states near the Fermi level, emphasizing the critical role of electronic structure in stabilizing the VOiHi complex. Furthermore, we investigate all these defects as potential qubit candidates by characterizing their magnetic properties and zero-phonon line energies.