First-principles studies of hydrogen irradiation effects on the photoluminescence properties of nitrogen-vacancy centers in 4H-SiC

Nitrogen-vacancy (NV) color centers in 4H-SiC have gained prominence in quantum technology as room-temperature controllable near-infrared single-photon sources and quantum bits, with various ion irradiation techniques employed for their fabrication; among these methods, hydrogen (H) ion irradiation has emerged as a particularly attractive approach because of its precision and minimal lattice damage. However, the influence of H on the photoluminescence (PL) properties of NV centers remains largely unexplored. In this work, we systematically investigate the effects of H irradiations using first-principles calculations. Our results reveal the dual roles of H in 4H-SiC: on the one hand, H can passivate $\mathrm{N}{\mathrm{V}}^{\ensuremath{-}}$ by inevitably forming $\mathrm{NV}{\mathrm{H}}_{\mathrm{n}}$ complexes; on the other hand, H can form new color centers $\mathrm{NV}{\mathrm{H}}^{\ensuremath{-}}\phantom{\rule{4pt}{0ex}}(\mathrm{S}=\frac{1}{2})$ with significantly lower zero-phonon line (ZPL) energies than $\mathrm{N}{\mathrm{V}}^{\ensuremath{-}}$, exhibiting PLs with no overlap with those of $\mathrm{N}{\mathrm{V}}^{\ensuremath{-}}$ in the range 1150--1450 nm. Our results not only reveal the underlying mechanism for the experimentally observed PL decay in $\mathrm{N}{\mathrm{V}}^{\ensuremath{-}}$ ensemble prepared via hydrogen irradiation but also suggest $\mathrm{NV}{\mathrm{H}}^{\ensuremath{-}}$ as a promising infrared single-photon source (SPS) in the IR-B region. We further elucidate the distinct PL characteristics of $\mathrm{N}{\mathrm{V}}^{\ensuremath{-}}$ and $\mathrm{NV}{\mathrm{H}}^{\ensuremath{-}}$ arising from their atomic configuration differences, providing detailed theoretical interpretations for experimental observations.