Angular dependence of the optical reflectance in two-dimensional Si-ZnO photonic crystals

In this work, we present an experimental study of the angular dependence of the optical reflectance in two 2-dimensional photonic structures, built on a silicon substrate coated with a ZnO thin film. Photonic structures studied describe a regular square lattice with a lattice constant a = 1.05 μm and circular air holes with a radius r = 0.63a. Additionally, one of these photonic structures contains a pattern of nine quasi-circular micro-cavities embedded in a regular square lattice photonic crystal, describing a secondary square lattice. A comparison of the optical reflectance of the two photonic structures as a function of the incidence angle for transverse magnetic polarization mode in the visible (Vis) and near-infrared (NIR) ranges of the electromagnetic spectrum was accomplished. Results obtained revealed a strong angular dependence of the reflective optical properties of the two 2-dimensional photonic structures on the illumination incidence angle. The photonic structure with the array of resonant optical cavities presented a very unusual behavior regarding the reflectance of the substrate, this because its reflectance described specific modulations dependent on the incidence angle of illumination.