Device contacts as spin-state selectors for silicon vacancies in 4H-SiC
Optically addressable defect spins in wide band gap semiconductors are promising building blocks for scalable quantum technologies. Yet, the consequences of conventional contact schemes used in semiconductor device integration for the quantum spin environment remain largely unexplored. Using the silicon vacancy (V$_\mathrm{Si}$) in silicon carbide (SiC) as a model system, we show that a widely used contact metal, nickel (Ni), intrinsically perturbs the defect spin state and quenches the characteristic emission from the spin-quartet channel of V$_\mathrm{Si}$. Low-energy muon spin rotation further reveals that Ni contacts create a magnetically contaminated region extending at least $\sim$120 nm into the SiC, in stark contrast to non-magnetic contacts such as Ti and Al. Moreover, cross-sectional cathodoluminescence measurements conducted on samples with box profiles of high defect density demonstrate a suppression of the quartet-state luminescence from the V$_\mathrm{Si}$ over a distance up to 500 nm beneath the Ni contact. This drastic influence on the defect's magnetic environment is accompanied by the appearance of a signature consistent with photoluminescence from the spin-doublet state of V$_\mathrm{Si}$ in the vicinity of the Ni layer, which was not observed in other material stacks. These results establish that even standard device configurations can drive quantum defects into unwanted charge and spin configurations, underscoring the necessity of precise design to preserve quantum-grade spin environments in semiconductor devices.