OPTICAL-PROPERTIES OF (BI1-XSBX)(2)SE-3 SINGLE-CRYSTALS

(Bi1-xSbx)(2)Se-3 (x = 0 to 0.2) single crystals prepared from element s of 5N purity by means of a modified Bridgman method were characteriz ed by measurements of infrared reflectance and transmittance. Values o f the plasma resonance frequency omega(p), optical relaxation time tau , and high-frequency permittivity epsilon(proportional to) were determ ined by fitting the reflectance spectra. It was found that the substit ution of Sb atoms for Bi atoms in the Bi2Se3 crystal lattice leads to an increase in the omega(p) values, whereas in the range of higher Sb content the omega(p) values decrease. This effect is accounted for by a model of point defects in the crystal lattice of (Bi1-xSbx)(2)Se-3. The dependence of the absorption coefficient K on the energy of incide nt photons was determined from the transmittance spectra. The Position of the short-wavelength absorption edge is discussed. with regard to the long-wavelength absorption edge it was found that the values of al pha in the relation K similar to lambda(alpha) lie in the interval 2.2 to 2.5, hence the dominant scattering mechanism of the free charge ca rriers in (Bi1-xSbx)(2)Se-3 crystals at room temperature is the scatte ring by acoustic phonons.