Thermoelectric Properties and Surface States in the Layers of Bi2Te3 Topological Insulators

Resumo

The thermoelectric properties and Shubnikov–de Haas (SdH) oscillations of monocrystalline layers of a topological insulator (ТI) of n-type bismuth telluride were investigated. The monocrystalline Bi₂Te₃ layers were fabricated by the mechanical exfoliations of layers from a monocrystalline ingot of the appropriate composition. The cyclotron effective masses, the Dingle temperature, and the quantum mobilities of charge carriers were calculated from the experimental data by SdH oscillations both in longitudinal (H ║ I) and in perpendicular (H ⊥ I) magnetic fields at temperatures in the range of 2.1–4.2 K. It was found that the phase shift of the Landau levels index is 0.5 both for the parallel and for the perpendicular magnetic fields associated with the Berry phase of surface states. The power factor in the temperature range of 2–300 K was calculated from the temperature dependences of resistance and thermal e.m.f. It was stated that the power factor α²σ has a maximum value in the temperature range of 100–250 K, which corresponds to the maximum values for perfect monocrystals described in the literature. Taking into account that the heat conductivity in the thin layers is essentially lower than in the bulk samples, it is reasonable to expect a considerable increase in the thermoelectric efficiency over a wide temperature range, which is of great importance for the development of new highly effective thermoelectric materials based on thinner Bi₂Te₃ ТI layers for practical applications in thermogenerators and coolers.