Optical and Galvanomagnetic Properties of Bi1-xSbx Thin Films in the Terahertz Frequency Range

Abstract

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.

Photothermal, Photoelectric, and Photothermoelectric Effects in Bi-Sb Thin Films in the Terahertz Frequency Range at Room Temperature

“…where ω = 2πν is an angular frequency of THz radiation, k is an extinction (absorption) coefficient, c is the speed of light in vacuum, σ is a conductivity, n is a refractive index, ε 0 is the vacuum permittivity, and τ is the relaxation time (see Table 1) which was previously estimated for the same samples in Reference [17].…”

“…The properties of Bi 1−x Sb x films were studied in the frequency range of 0.1-0.2 THz by means of terahertz time-domain spectroscopy based on InAs THz generator irradiated by an infrared femtosecond laser (1040 nm, 200 fs, 70 MHz, 15 nJ) in the previous work for 70 nm and 150 nm films [17]. These studies were performed at a temperature of 290 K. The THz waveforms passed through the air, the bare mica substrate and the film-on-substrate structures were recorded and then were used to calculate the corresponding spectra of complex electric field amplitudes (amplitudes and phases) using the fast Fourier transformation.…”

“…where d f ilm is the film thickness (measured by Linnik's interferometry), and ε 0 is the permittivity of the free space. The conductivity/permittivity spectra measured for 70 nm and 150 nm films [17] were well approximated using the classical Drude model. Then, the model parameters were linearly extrapolated to the thickness of 200 nm to obtain the complex permittivity of the films studied in this work.…”

Experimental investigation of optically controlled topological transition in bismuth-mica structure

“…To obtain thin bismuth films, the thermal spraying method in a vacuum 12 was used. This method consists in converting the substance on the evaporator into a gaseous state and depositing it on a substrate located above the evaporator.…”

“…Dielectric plays an important role as a substrate for a thin film considered as such due to a high ratio of wavelength to film thickness. It was also shown that usage of Bi Sb alloys with variable antimony concentration x instead of Bi films allows to tune the parameters of hyperbolic media 12 . In particular, at a certain antimony concentration, the semimetal-semiconductor transition occurs in Bi Sb alloys 13 .…”