Doping tunable resonance: Toward electrically tunable mid-infrared metamaterials

We demonstrate metamaterials at the mid-infrared (mid-IR) wavelengths (8–12 μm) that can be widely tuned by doping in adjacent semiconductor epilayers. The metamaterials are based on metallic split ring resonators (SRRs) fabricated on doped indium antimonide (InSb). Finite integral time-domain simulation results and measured transmission data show that the resonance blueshifts when the semiconductor electron carrier concentration is increased while keeping the split ring geometry constant. A resonant wavelength shift of 1.15 μm is achieved by varying the carrier concentration of underlying InSb epilayer from 1×1016 to 2×1018 cm−3. This work represents the first step toward active tunable metamaterials in the mid-IR where the resonance can be tuned in real time by applying an electric bias voltage to control the effective carrier density.