Anomalous dispersion engineering of co-sputtering Ag-AZO hybrids for antireflection coatings

Conventional antireflection coatings (ARCs), including single- and multi-layer, bionic micro/nano, and gradient-index structures, often do not take anomalous dispersive materials into account, but normal dispersion and Rayleigh configuration, known as a step-down index profile, in which low refractive index (RI) materials are adjacent to incident media and the high RI ones, are located on substrates. We found that the anomalous dispersive materials could be good candidates for novel sub-100 nm ARCs, considering the ab-initio impedance matching designs. Engineering the anomalous dispersion of co-sputtering Ag-AZO hybrid materials, two types of ARCs were fabricated on silicon substrates: a 70 nm tri-layer reverse-Rayleigh and a 140 nm bi-layer Rayleigh for comparison. We observed that both exhibited the average reflectance of 5.46% and 1.49% at the wavelength range from 400 to 780 nm, respectively, and were much lower than that of bare silicon, 38.02%, where the underlying origin for the reverse-Rayleigh AR was discussed. The studies on the engineering and integration of anomalous dispersive materials into ARCs and optical elements would be of great significance for compact light harvesting, energy conversion, and radar stealth technology.