Дефекты межслоевой поверхности и термоэлектрические свойства в слоистых пленках топологических изоляторов n-Bi-=SUB=-2-=/SUB=-Te-=SUB=-2.7-=/SUB=-Se-=SUB=-0.15-=/SUB=-S-=SUB=-0.15-=/SUB=-

Interlayer surface defects and thermoelectric properties in layered films of n-Bi2Te2.7Se0.15S0.15 topological insulators L. N. Lukyanova*, O. A. Usov, M. P. Volkov, V. A. Rusakov Ioffe Institute Russian academy of science, 194021 St.Petersburg, Russia *E-mail: [email protected] Abstract In layered films of n-Bi2Te2.7Se0.15S0.15 topological insulators optimized for temperatures below room temperature, the morphology of the (0001) interlayer surface and thermoelectric properties were studied. On the profiles of the (0001) surface, we identified neutral impurity defects arising from the substitution of Se and S atoms for Te atoms and donor antisite defects of tellurium at bismuth sites, which affect the thermoelectric properties. The average value of thermoelectric figure of merit in n-Bi2Te2.7Se0.15S0.15 films increases to <Z> ≈ 3.0•10-3 K-1 in the range 80 – 215 K, while in bulk solid solution <Z> ≈ 2.0•10-3 K-1. An increase in the thermoelectric figure of merit in films is associated with an increase in the energy dependence of the relaxation time due to an increase in the effective scattering parameter reff. It is shown that in films the Seebeck coefficient, the density of states effective mass m/m0, and the material parameter proportional to the power factor increase, while the lattice κL and electronic thermal conductivity κe decrease, which determines the increase in thermoelectric figure of merit.

Growth of Heavily Indium Doped Si Crystals by Co-Doping of Neutral Impurity Carbon or Germanium

Czochralski Growth of Si Crystals Heavily Doped with in Impurity and Co-Doped with Electrically Neutral Impurity C or Ge Was Conducted in Order to Investigate the Solubility and Ionization Ratio of in in Si for Utilizing in Advanced ULSI and PV Devices. The Carrier Concentrations in the Grown in-Doped and (In+C) and (In+Ge) Co-Doped Crystals Were in a Range of 3.5~6.5 × 1016 Cm-3, much Lower than the Total Concentration of in Impurity due to the Low Ionization Ratio. Sufficient Increase of Carrier Concentrations by Co-Doping of C or Ge Impurity Was Not Detected for their Low Concentrations in the Grown Crystals Investigated.

Effects of Non-Continuous TiO2 Buffer Layers on Structural and Electrical Properties of Indium Tin Oxide Thin Films

Indium Tin Oxide (ITO) films on polyethylene terephthalate (PET) sandwiching TiO2 buffer layers with different sputtering time have been prepared by rf-magnetron sputtering. Scanning Electron Microscope images of the TiO2 buffer layers showed the non-continuous growth in a typical sputtered film growing process. (400) oriented diffraction peaks appeared in all the ITO/TiO2/PET films. The electrical properties were measured by four point probe method and van der Pauw method. The variations of the resistivity and hall mobility on the sputtering time of TiO2 layer were studied. Furthermore, an exponential decay correlation of resistivity and the grain size was fitted. But the linear relationship between the ITO grain size and the mobility indicated by the grain boundary scattering theory didn’t appear here. The reason is believed to neglect the influence of the local variations of the lattice spacing and some other important scattering mechanisms such as lattice, ionized impurity, neutral impurity scattering, etc.