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We report results of galvanomagnetic and terahertz time-domain spectroscopy measurements on thin films of Bi 1−x Sb x on polyimide and mica substrates with various antimony concentrations (x from 0 to 15 %) and film thickness (70, 150 nm). The resistivity, Hall coefficient and magnetoresistivity of the films were measured experimentally in the magnetic field of 0.65 T at room temperature. Mobility and concentration of electrons and holes in the film plane were calculated using the transport coefficients. The terahertz time-domain spectroscopy is used to measure the complex conductivity and permittivity of Bi 1−x Sb x thin films on the dielectric substrates in the frequency range from 0.2 to 1 THz. The plasma frequency, relaxation time, DC conductivity and effective carrier mass were extracted from these data and evaluated as functions of the Sb concentration for different film thickness and substrate. We observed that the film magnetoresistivity decreases with increasing the Sb concentration and for most of the films the Hall coefficient is negative and depends on the external factors insignificantly. We show that the mobility of charge carriers weakly depends on Sb concentration, which confirms the assertion about the scattering of carriers on themselves and not on defects in the structure. It was revealed that film static and dynamic resistivity (conductivity) as well as dielectric permittivity depend on Sb content and the film thickness. The results may be used for development of various thermoelectric, electronic and optical devices, such as THz detectors or components which can control the properties of THz radiation.

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The terahertz frequency range is promising for solving various practically important problems. However, for the terahertz technology development, there is still a problem with the lack of affordable and effective terahertz devices. One of the main tasks is to search for new materials with high sensitivity to terahertz radiation at room temperature. Bi1−xSbx thin films with various Sb concentrations seem to be suitable for such conditions. In this paper, the terahertz radiation influence onto the properties of thermoelectric Bi1−xSbx 200 nm films was investigated for the first time. The films were obtained by means of thermal evaporation in vacuum. They were affected by terahertz radiation at the frequency of 0.14 terahertz (THz) in the presence of thermal gradient, electric field or without these influences. The temporal dependencies of photoconductivity, temperature difference and voltage drop were measured. The obtained data demonstrate the possibility for practical use of Bi1−xSbx thin films for THz radiation detection. The results of our work promote the usage of these thermoelectric materials, as well as THz radiation detectors based on them, in various areas of modern THz photonics.

Hyperbolic medium is a special class of strongly anisotropic materials described by diagonal permittivity tensor with the principal components being of the opposite signs, which results in a hyperbolic shape of isofrequency contours. These media support propagating electromagnetic waves with extremely large wave vectors exhibiting unique optical properties and applications such as negative refraction, subwavelength imaging, radiative heat transfer manipulation, enhancing spontaneous emission rate (Purcell factor), biosensing, and nanoscale light confinement. Hyperbolic metamaterials have been experimentally realized for optical, infrared, and microwave frequency ranges. For the terahertz (THz) frequency range, graphene‐based and bismuth‐based media are only theoretically predicted to have a hyperbolic dispersion relation. Herein, the experimental evidence of such dispersion in bismuth–dielectric materials at THz frequencies is shown. THz waveforms transmitted through ultrathin bismuth film/dielectric substrate structures are measured and the negative time delay caused by transition between the elliptic and hyperbolic dispersion at bismuth thickness increase is revealed. In the hyperbolic regime, the switching between effective near‐zero and negative refractive index regime is demonstrated, which depends on the bismuth film thickness and dielectric substrate optical properties. The outcomes demonstrate the possibility for realizing easy planar hyperbolic media for THz photonics, sensing, imaging, and communication systems.