Some physical properties of Hf-doped Sb/sub 2/Te/sub 3/ single crystals

Single crystals of Hf-doped Sb/sub 2/Te/sub 3/ (c/sub Hf/ = 0-2.4x10/sup 19/cm/sup -3/) were prepared from the elements of Sb, Hf, and Te of the 5N purity by a modified Bridgman method. The obtained crystals were characterized by the measurements of the reflectance R in the plasma resonance frequency region. Values of the plasma resonance frequency, /spl omega//sub p/, were determined by fitting the reflectance spectra using the relations for the real and imaginary parts of the complex dielectric function, following from the Drude-Zener theory. From the observed changes in the value /spl omega//sub p/ it was concluded that the doping of Hf atoms into the crystal structure of Sb/sub 2/Te/sub 3/ results in a decrease in the concentration of free current carriers - holes. This conclusion was confirmed by the measurement of temperature dependencies of the Hall coefficient R/sub H/, electrical conductivity /spl sigma/, and the Seebeck coefficient /spl alpha/, within the temperature range of 100-400K. Moreover, temperature dependences of the power factor /spl sigma//spl alpha//sup 2/ and mobility /spl mu//spl sim/R/sub H/./spl sigma/ of free carriers are discussed.