Dispersion control in a near-infrared subwavelength resonator with a tailored hyperbolic metamaterial.

We demonstrate experimentally and computationally an intricate cavity size dependence of the anomalous near-infrared mode spectrum of an ordinary optical resonator that is combined with a ZnO:Ga-based hyperbolic metamaterial (HMM). Specifically, we reveal the existence of a resonance in subwavelength-sized cavities and demonstrate control over the first-order cavity mode dispersion. We elaborate that these effects arise due to the HMM combining the mode dispersions of purely metallic and purely dielectric cavity cores into a distinct intermediate regime.

Revealing the competing contributions of charge carriers, excitons, and defects to the non-equilibrium optical properties of ZnO.

Due to its wide band gap and high carrier mobility, ZnO is, among other transparent conductive oxides, an attractive material for light-harvesting and optoelectronic applications. Its functional efficiency, however, is strongly affected by defect-related in-gap states that open up extrinsic decay channels and modify relaxation timescales. As a consequence, almost every sample behaves differently, leading to irreproducible or even contradicting observations.

Demonstration of hyperbolic metamaterials at telecommunication wavelength using Ga-doped ZnO.

Hyperbolic metamaterials (HMMs) have attracted much attention because they allow for broadband enhancement of spontaneous emission and imaging below the diffraction limit. However, HMMs with traditional metals as metallic component are not suitable for applications in the infrared spectral range. Using Ga-doped ZnO, we demonstrate monolithic HMMs operating at infrared wavelengths.

Negative refraction at telecommunication wavelengths through plasmon-photon hybridization.

We demonstrate negative refraction at telecommunication wavelengths through plasmon-photon hybridization on a simple microcavity with metallic mirrors. Instead of using conventional metals, the plasmonic excitations are provided by a heavily doped semiconductor which enables us to tune them into resonance with the infrared photon modes of the cavity. In this way, the dispersion of the resultant hybrid cavity modes can be widely adjusted.

Enabling novel functionality in heavily doped ZnO:Ga by nanostructuring: an efficient plasmonic refractive index sensor.

We demonstrate a proof-of-concept refractive index sensor based on heavily doped ZnO:Ga nanostructured in a grating configuration, which supports free space excitation of propagating surface plasmons. The bulk sensitivity of the sensor of 4.9 × 10(3) nm per refractive index unit, achieved in the mid-infrared spectral range with the first grating prototype, surpasses that of the noble metal counterparts by three to four times.

Ultrafast Nonlinear Response of Bulk Plasmons in Highly Doped ZnO Layers.

Longitudinal bulk plasmons in an n-doped ZnO layer system are studied by two-color femtosecond pump-probe spectroscopy in the midinfrared. The optical bulk plasmon resonance identified in linear reflectivity spectra undergoes a strong redshift and a limited broadening upon intraband excitation of electrons. The nonlinear changes of plasmon absorption decay on a time scale of 2 ps and originate from the intraband redistribution of electrons.

Band-offset engineering in organic/inorganic semiconductor hybrid structures.

Control over the electronic structure of organic/inorganic semiconductor interfaces is required to realize hybrid structures with tailored opto-electronic properties. An approach towards this goal is demonstrated for a layered hybrid system composed of p-sexiphenyl (6P) and ZnO. The molecular orientation can be switched from "upright-standing" to "flat-lying" by tuning the molecule-substrate interactions through aggregation on different crystal faces.