Thermoelectric Properties of Films and Monocrystalline Whiskers of Tellurium
Tellurium is an interesting semiconductor for thermoelectric applications because its thermopower is high (500 muV/K). Its figure of merit is low in the bulk because it has high thermal conductivity. However, in confined geometries, the phonon conductivity decreases due to phonon scattering. Therefore we have investigated the thermoelectric properties of Te films and whiskers. We report a study of the thermoelectric properties of Te films obtained by vacuum-condensation method on glass, polyamide, mica at various temperatures of condensation. The crystallographic structure of the films is characterized by the distribution function of the grain major axis. It is shown that the films condensed at 433 K possess the highest mobility. Te whiskers were grown from the paragas phase and they were single crystals in the form of hexahedral cylinder having cavities inside. When deposited on cold substrate, the cylinders had no cavities. The direction of the whisker crystal growth was always [0001] with respect to the whiskers length. It is shown that in films with the thickness of ~1 mum, the room temperature thermopower S is 330 muV/K and increases with temperature increasing (S = 450 muV/K at 450 K). The resistivity decreases with the temperature growth, as a result the power factor alpha2sigma increases by almost a factor of two. The 77 K electric conductivity of Te whiskers is 2-to-3 order-of-magnitude higher than in bulk crystals, presumably due to high structural perfection of whisker crystals. The thermopower in the range of 300 K is S = 400-750 muV/K
Field effect in tellurium
Abstract Field effect measurements were performed on pure p-type tellurium single crystals between 4.2 and 250K. Inversion of the surface conductance from a p-type accumulation layer was achieved with external fields of about 106 V/cm. The density and energy of surface states is estimated.
Quantum Effects in Cyclotron Resonance in p-Type Tellurium
Quantum effects of cyclotron resonance of holes have been observed in tellurium by using high-resolution HCN and ${\mathrm{D}}_{2}$O submillimeter laser spectrometers. The multiplicity of resonance absorption lines in both parallel and perpendicular directions with respect to the principal axis suggests complex energy surfaces with highly warped bands. In addition, cyclotron resonance of electrons thermally excited across the gap was obtained.