Properties of Sb2Te3, Single Crystals Doped with Tl Atoms

(Bi0.5Sb0.5)2Te3 single crystals doped with In atoms (cIn = 0 to 9.8 × 1020 cm−3) are prepared by the modified Bridgman method. From the analysis of the measurements of reflection spectra in the plasma resonance-frequency region, electrical conductivity, and the Seebeck coefficient it is found that an increase in the concentration of In atoms in the crystal lattice of (Bi0.5Sb0.5)2Te3 crystals results in a decrease in the hole concentration. This effect is explained by the formation of substitutional point defects of In or In which result in an increase in the bond polarity of the structural lattice. The higher ionicity of the chemical bonds in the mixed crystals leads to a decrease of the concentration of antisite defects of Bi and Sb with a simultaneous decrease of the free current carriers, i.e. holes.

Bi0.5Sb0.5)2Te3 Crystals Doped with Indium Atoms

The influence of doping with Tl on the Shubnikov-de Haas effect at T = 4.2 K in magnetic fields up to 38 T in p-Sb2−x
 Tl
 x
 Te3 (x = 0, 0.005, 0.015, and 0.05) and n-Bi2−x
 Tl
 x
 Se3 (x = 0, 0.01, 0.02, 0.04, and 0.06) single crystals is investigated. Extreme cross-sections of the Fermi surface in both materials decrease upon doping with Tl: the hole concentration decreases in Sb2−x
 Tl
 x
 Te3 due to the donor effect of Tl and the electron concentration in n-Bi2−x
 Tl
 x
 Se3 decreases due to the acceptor effect of Tl. The temperature dependences of the Seebeck coefficient, electrical conductivity, thermal conductivity, and dimensionless thermoelectric figure of merit in a temperature range of 77–300 K are measured. The thermal conductivity and electrical conductivity decrease upon doping with Tl both in p-Sb2−x
 Tl
 x
 Te3 and in n-Bi2−x
 Tl
 x
 Se3. The Seebeck coefficient increases in all compositions upon an increase in doping over the entire measured temperature range. The thermoelectric figure of merit increases upon doping with Tl.

The Shubnikov-de Haas effect and thermoelectric properties of Tl-doped Sb2Te3 and Bi2Se3

Single crystals of Sb1.5Bi0.5Te3 doped with Ag atoms (c Ag = 0-3.5 × 1019 atoms/cm3) were characterized by X-ray diffraction, measurement of reflectance in the plasma resonance frequency region, Hall coefficient, electrical conductivity, Seebeck coefficient and the figure of merit. It was found that Ag atoms in the crystal structure of Sb1.5Bi0.5Te3 behave like acceptors; up to the concentration of c Ag ≅ 1.7 × 1019 atoms/cm3 they increase the hole concentration, whereas in the concentration region of c Ag ≅ (1.7–3.5) × 1019 atoms/cm3 the hole concentration does not change. The incorporation of Ag atoms into the Sb1.5Bi0.5Te3 crystal structure results in a decrease in the elementary cell volume and a decrease in the value of figure of merit. The increase in the hole concentration is ascribed to the formation of substitutional defects of Ag”Sb, or Ag'Sb. Besides these defects the formation of interstitial ions of Agi and four-layer-lamellae of the type [Ag0.5Sb0.5]-Te-[Ag0.5Sb0.5]-Te is suggested.

Characterization of Ag-doped Sb1.5Bi0.5Te3 single crystals

Single crystals of Bi 1.5 Sb 0.5 Te 3 doped with Ag atoms (C Ag = 0 - 4.34x10 19 atoms/cm 3 ) were characterized by measurement of Hall coefficient, electrical conductivity, Seebeck coefficient and the figure of merit. It was found that Ag atoms in the crystal structure of Bi 1.5 Sb 0.5 Te 3 behave like donors. It is necessary to add more than one Ag atom to the Bi 1.5 Sb 0.5 Te 3 compound in order to suppress the hole concentration by one hole. Such a behaviour of the dopant is explained by the formation of various structural defects. Besides the dominant interstitial defects of Ag 1 silver atoms form also positively charged substitutional defects Ag Sh , Ag' Sh , and a four-layer-lamellae of the type [Ag 0.5 Sb 0.5 ]-Te-[Ag 0.5 Sb 0.5 ]-Te. The incorporation of Ag atoms into the Bi 1.5 Sb 0.5 Te 3 lattice, besides the suppression of the hole concentration, leads to a decrease in the figure of merit Z.

Characterization of Ag‐Doped Bi1.5Sb0.5Te3 Single Crystals

The effect on transport properties of the addition of 0.5-5% Tl2Te3 to p-type solid solutions of antimony and bismuth tellurides was studied. It was found that the addition of Tl2Te3 caused a lessening of the increase of hole concentration as low temperatures were approached, resulting in a slower decrease of the Seebeck coefficient with a decrease in temperature.

A. Sher

Papers

The effect of Tl 2 Te 3 on the properties of the solid solution (Sb 2 Te 3 ) 0.75 .(Bi 2 Te 3 ) 0.25