Size effects in the galvanomagnetic and thermoelectric properties of ultrathin bismuth-antimony films

The paper presents the results of a study of the electrical, galvanomagnetic, and thermoelectric properties of Bi and Bi_1–xSb_x (x = 0.03, 0.05, and 0.12) thin films (10–50 nm) on a mica substrate. All samples are characterized by an increase in conductivity with a decrease in film thickness, which can be associated with the presence of topologically protected surface states. It has been found that the band structure of the alloys significantly affects the appearance of the metallic type of conductivity in films with a ≤ 18 nm thickness. It was found that the resistivity of Bi_0.97Sb_0.03 films ≤ 17 nm thick is almost independent of temperature. Despite the increase in the conductivity of the samples, with a decrease in the thickness, the thermoelectric power factor decreases, which casts doubt on the fact that surface states have a positive effect on the thermoelectric figure of merit of thin Bi_1–xSb_x films. However, the detection of a positive thermoelectric power in Bi_0.88Sb_0.12 samples may be of interest in the development of the p branch of thermoelectric converters.