Enhanced dielectric dispersion, light absorption and optical conduction in a-Si/Fe/a-Si gigahertz/terahertz electro-optical band filters

Here, we investigate stacked amorphous-silicon (a-Si) layers embedding Fe nanosheets. While the Fe nanosheets do not perturb the amorphous matrix, we observe pronounced improvements in the optical and electronic responses: optical absorption, dielectric response, optical conductivity, and the terahertz cut-off frequency are all enhanced. Incorporation of Fe sheets increases the absorption by more than 100 %. The absorption enhancement, evaluated across multiple samples with associated error bars, reaches up to 832 % at 1.70 eV. Embedding Fe nanosheets narrows the optical band gap and raises the static dielectric constant by 64.5 %. The optical conductivity and terahertz cut-off frequency rise by more than 1000 % and ∼ 600 %, respectively. Drude–Lorentz analysis of the conductivity spectra indicates the feasibility of a-Si/Fe/a-Si stacks as terahertz band-pass filters, supporting carrier drift mobility up to 30.40 cm2 V−1 s−1. In addition, electrical measurements show an abrupt conductivity increase and a transition to metallic behavior. At microwave frequencies, the a-Si/Fe/a-Si interfaces exhibit GSM-1800 (1.8 GHz)/quad-band band-pass filter characteristics compatible with contemporary mobile-network deployments, and the filter design and performance are consistent with commercially available alternatives. Additionally, point antennas were designed and exhibited excellent performance, including up to 2.2 GHz matched bandwidth, Reflection parameter deeper than –30 dB, and isolation below –15 dB across the operating range (1 k-6.0 GHz).