Hybrid indium tin oxide-Au metamaterial as a multiband bi-functional light absorber in the visible and near-infrared ranges

Metamaterial nearly perfect light absorbers (MPAs) with dual-narrowband functionality-that absorb light in two narrowband adjacent wavelength regions-have attracted considerable attention due to their intriguing applications, such as sensing, photovoltaic, and thermal emission. Here, we propose a multi-band MPA with two narrowband absorption responses that are centered on the visible and near-infrared (NIR) wavelengths (773 nm and 900 nm, respectively) and a broadband absorptive characteristic in another window in the NIR region (ranging from 1530 nm to 2700 nm with a bandwidth of 1170 nm). The MPA comprises a periodic array of self-aligned hybrid indium tin oxide (ITO)-Au split-ring-resonators that are separated from an optically thick bottom reflector with a SiO2 layer. Based on numerical calculations, which are accompanied with a semi-analytical examination, we find that the dual narrowband and broadband responses are attributed to the hybridization of the optical responses of gold as a plasmonic material with the ones of ITO. Note that ITO acts as a low-loss dielectric in the visible range and a lossy plasmonic material in the NIR region. Moreover, due to the applied symmetry in the unit cell of the metamaterial, the proposed MPA represents polarization insensitive and omnidirectional absorptive features. The proposed metastructure can find potential applications in selective thermophotovoltaic devices, thermal emitters, and sensors.