## 1 Introduction  
Terahertz (THz) devices are of significant importance for such fields as disease diagnostics and medical imaging [1; 2; 3], security systems [4; 5], and sensing and imaging [6]. Thermal THz sensors, such as bolometers, are used for THz detection [7]. The effect of electromagnetic heating due to THz radiation absorption can be used as the signal for thermoelectric (TE) detector. TE detectors work on the basis of the Seebeck effect, which generates electric voltage in TE circuits in case of temperature difference between two junctions (hot and cold junctions) of TE materials [8; 9]. Basically, the temperature of cold junction is maintained at room temperature, while hot junction temperature is to be increased due to the electromagnetic heating. In literature, the effect combining optical and thermoelectric phenomena is called photothermoelectric, and it has been studied with the use of different advanced materials: graphene [10], single-layered \(MoS_{2}\)[11], \(Bi_{2}Se_{3}\) nanoribbons [12], and organic thermoelectrics [13]. A line of works about THz detectors working on the TE effect have been published. In [14], a responsivity of several hundred VW\({}^{-1}\) was reported for a detector based on single-layer graphene on 300-nm \(SiO_{2}\) substrate. A THz TE detector based on carbon nanotubes with responsivity of several VW\({}^{-1}\) was reported in [15]. The increase of efficiency or responsivity of TE detector is possible due to the increase of temperature difference between junctions or due to the increase of TE figure of merit \(Z\). \(Z\) is proportionalto Seebeck coefficient squared \(S^{2}\) and electrical conductivity \(\sigma\); \(Z\) is inversely proportional to thermal conductivity \(\kappa\). In order to increase temperature difference, the cross-section of hot junction can be decreased. The hot junction can be thermally insulated, for example, in vacuum, and the device can be encapsulated in order to prevent convection. Besides of temperature difference increase, the usage of low-dimensional TE materials interconnects with \(Z\)-value improvement. It was shown that 2D and 1D thermoelectrics could give a significant increase of TE figure of merit [16]. In particular, TE thin films are known for the possibility to produce a high Seebeck coefficient and power factor \(S^{2}\cdot\sigma\). As all thermoelectric properties are the functions of temperature, not every material will be suitable for detecting purposes requiring near-room temperatures. TE films based on \(Bi\) and \(Te\) alloys are good candidates for the applications at room temperature, their properties have been reported in [17]. Other candidates are TE films based on \(Bi\) and \(Sb\) solid solutions. In a \(Bi_{(1-x)}Sb_{(x)}\) system with Sb concentration lower than 15%, the Seebeck coefficient value at room temperatures is around \(-100\)\(\mu\)V/K. This system was studied in the works of [PERSON] et al. in the 1990s [18] and [PERSON] et al. in 2017 [19]. Close values of Seebeck coefficient have been reported for the \(Bi_{0.91}Sb_{0.09}\) system in [20]. In an article published by [PERSON] et al. in 2018 [21], a Seebeck coefficient of \(Bi_{87}Sb_{13}\) was around \(80\)-\(110\)\(\mu\)V\(\cdot\)K\({}^{-1}\) with comparatively low thermal conductivity (1.5-3.5 W\(\cdot\)m\({}^{-1}\)K\({}^{-1}\)) and high electrical conductivity (around 100-300 KS-m\({}^{-1}\)) at room temperatures. Sb thin film was used in our study as a possible p-type material, which can have a good agreement in electrical conductivity with Bi-Sb solid solutions. Seebeck coefficient of Sb is around 30 \(\mu\)V/K [22]. Moreover, the presence of a narrow band gap makes it possible for Bi-Sb to absorb THz radiation. The band structure of Bi-Sb may be seen in [23], the results have been taken from the work published in 1970 [24]. Surface band structure of \(Bi_{(x-1)}Sb_{(x)}\) was reported in [25].