Phase-Dispersion-Engineered Nanoscale SiO ₂ /TiO ₂ /SiO ₂ Trilayer Antireflection Coating: A Practical Route for High-Performance Silicon Photodetectors

Broadband and omnidirectional antireflection is essential for maximizing the optical efficiency of silicon photodetectors. Conventional antireflection strategies─including graded-index multilayers and photonic crystal structures─can broaden spectral response; however, they typically require thick layer stacks that induce significant thermal and mechanical stress during integration with silicon devices. Such structural limitations hinder reliable implementation in practical silicon photodetector platforms. Here, we introduce an ultrathin antireflection multilayer based on phase dispersion engineering and optical admittance matching, where the SiO 2 /TiO 2 /SiO 2 layer thicknesses are selected to suppress admittance mismatch and its spectral and angular gradients under a 178 nm total thickness constraint. By tailoring the spectral phase response of the trilayer, the proposed structure stabilizes the optical admittance across the broad angular and spectral range targeted to silicon absorption wavelengths. The proposed phase-dispersion-driven mechanism enables broadband destructive interference within a nanoscale thickness, thereby overcoming the trade-off between optical bandwidth and structural thickness that limits conventional multilayer designs. The resulting ultrathin SiO 2 /TiO 2 /SiO 2 coating achieves an average reflection of ∼3% from 450 nm to 1100 nm for incident angles up to 70°, while maintaining polarization-independent operation. Integration with a CMOS-compatible silicon photodetector using a low-thermal-budget reactive sputtering process yields a peak responsivity of 0.64 A/W at 900 nm, corresponding to a 43.7% enhancement. This nanoscale all-dielectric SiO 2 /TiO 2 /SiO 2 trilayer establishes a lithography-free, integration-compatible antireflection platform for cost-effective silicon photodetectors with broadband, omnidirectional, and polarization-independent operation.