Tunable near-infrared perfect absorber based on the hybridization of phase-change material and nanocross-shaped resonators

Abstract

Ge2Sb2Te5 (GST) is a kind of non-volatile chalcogenide phase-change material, which has a significant difference in permittivity between its amorphous and crystalline states in the infrared range. On account of this remarkable property, the combination of GST and metamaterials has great potential in tunable meta-devices. In this paper, a perfect absorber based on a nanocross-resonator array stacked above a GST spacer layer and an Au mirror (i.e., a metal-dielectric-metal configuration) is designed and experimentally demonstrated. A thin indium tin oxide (ITO) protective layer is inserted between the GST spacer and the Au resonator to avoid heat-induced oxidation of the GST layer during phase transition. We found that the ITO layer not only can protect the GST layer from deterioration, but also allows a significant blue shift in the absorption peak from 1.808 μm to 1.559 μm by optimizing the thickness of the two dielectric layers without scaling down the size of the metal structure, which provides a more feasible idea in pushing the absorption peak to higher frequency. The LC circuit model is presented to explain this blue-shift phenomenon, which is mainly attributed to the engineering of the dielectric environment of the parallel plate capacitance. In addition, such good performance in dynamitic modulation makes this perfect absorber a robust candidate for optical switching and modulating in various situations.