CHARACTERIZATION OF BI2SE3 CRYSTALS HIGHLY DOPED WITH PB

Pb-doped Bi2Se3 crystals were prepared from starting elements Bi, Se a nd Pb of 5N purity in the concentration interval c(Pb) = 0 - 4 x 10(25 ) Pb atoms m(-3) by a modified Bridgman method. The measured values of the transmittance and reflectance were used to determine the dependen ce of the absorption coefficient K on the photon energy for crystals w ith various values of c(Pb) and to prove the shift of the short-wavele ngth absorption edge with c(Pb). On the basis of the assumption of the validity of the ''single valley'' model, which can describe the lowes t conductivity band of Bi2Se3, and using the values of the free-carrie r effective mass in the directions perpendicular and parallel to tile trigonal axis c we determined the value of the reduced Fermi energy et a as 300 K for crystals with various values of c(Pb). Using the value of eta, we calculated the dependence of the Seebeck coefficient on c(P b) and compared it with the experimentally determined values. The comp arison has shown that the increasing content of Pb atoms in the Bi2Se3 lattice leads to a suppression of the role of the mechanism of scatte ring by ionised impurities; at higher concentrations of Pb in the crys tal the mechanism of scattering of free carriers by acoustic phonons b ecomes dominant. Further, the ideas on the nature of the point defects in the Bi2Se3(Pb) crystals are presented and the ''anomalous'' depend ence of the free-electron concentration on c(Pb) is qualitatively acco unted for.