Photoionization Current Spectroscopy of Individual Silicon Vacancies in Silicon Carbide

Defect charge-state dynamics are central to both spin-photon interfaces and photoelectrical spin readout. Despite the significance of silicon vacancies (V1/V2) in silicon carbide (4H-SiC) for both applications, their ionization behavior has remained unclear because conventional optical charge-state analysis is prevented by undetectable optical blinking. Here, we employ photocurrent spectroscopy of individual defects to measure the wavelength-dependent ionization cross sections. We reveal similar ionization cross sections for V1 and V2, increasing toward shorter wavelengths, while carbon vacancies dominate the more steeply increasing background photocurrent. These results indicate that, under resonant excitation at the respective ZPLs, V2 is less susceptible to photoionization, and its surrounding background defects are less ionized than V1. We also identify wavelength regimes that optimize defect-origin photocurrent for photoelectrical spin readout relative to background contributions, which differ between single-defect and ensemble measurements. Our results establish photocurrent spectroscopy as a powerful complement to optical methods, advancing defect-based quantum device development.