Search

This report demonstrates tunable carrier densities in CdO thin films through local ion irradiation, providing lateral control of mid‐IR optical properties. Ion‐solid interactions produce donor‐like defects that boost electron concentrations from the practical minimum of 2.5 × 1019 cm−3 to a maximum of 2.5 × 1020 cm−3 by metered ion exposure. This range is achieved using He, N, Ar, or Au ions at 1–2.8 MeV; when normalized by displacements per atom, all ion species produce comparable results. Since CdO is well‐described by the Drude model, irradiation‐tuned carrier densities directly alter the infrared dielectric function, and in turn, mid‐infrared optical properties. Further, it is demonstrated that by combining irradiation with traditional lithography, CdO films expose to ions in the presence of 3‐µm thick, patterned photoresist exhibit lateral carrier density profiles with ≈400‐nm resolution. Scanning near‐field optical microscopy reveals sharp optical interfaces with almost no companion contrast in surface morphology, microstructure, or crystallinity. Finally, CdO lateral homostructures supporting surface plasmon polaritons (SPPs) are demonstrated whose dispersion relation can be tuned through periodic patterning in a monolithic platform by simple nanofabrication. Numerical simulations show these polaritons result from strong coupling between excitations at CdO plasma frequencies and SPPs supported by the platinum substrate. [ABSTRACT FROM AUTHOR]

The epsilon‐near‐zero (ENZ) frequency regime of transparent conducting oxide materials is known to yield large enhancements in their optical nonlinearity and electro‐optic response. Here, Faraday rotation is investigated in Gd and In‐doped CdO films and it is found that the Verdet constant peaks at values >3 105 deg T−1 m−1 near the ENZ frequency, which is tunable in the wavelength range 2 < λ< 10 µm by varying the doping concentration. These results are among the highest reported to date in the mid‐infrared spectral range and are in good agreement with the Drude model, which confirms that the magneto‐optic response of doped CdO derives from its free carriers. The combination of a tunable Verdet constant, low optical loss compared to other plasmonic materials, and the ability to deposit CdO on Si with no loss in performance make this material a promising platform for integrated magneto‐optic and magnetoplasmonic devices that operate across the mid‐infrared. [ABSTRACT FROM AUTHOR]