Ozone-based postprocessing for resonance tuning of ultrahigh-<i>Q</i> Si photonic crystal nanocavities

Silicon (Si) photonic crystal nanocavities with high-quality ( Q ) factors and small modal volumes are promising candidates for applications. However, inevitable fabrication-induced structural imperfections cause deviations in resonant wavelengths from the target value, limiting practical applicability. To address this issue, we present an ozone-based postprocessing technique of sub-nanometer surface oxidation and removal of the oxide layer followed by hydrofluoric acid (HF) etching. This technique enables precise and reproducible tuning of resonance under ambient conditions without the need for vacuum or thermally complex equipment. Using this method, we demonstrate resonant wavelength shifts of 0.6 nm and 1.6 nm via ozone oxidation and subsequent HF treatment, respectively. In addition, we show improvement of Q factor by 40% compared to the as-fabricated nanocavity through the postprocessing. Our results prove a simple and CMOS-compatible method for tuning and enhancing the performance of Si photonic crystal nanocavities.