OPTICAL-PROPERTIES OF TITANIUM-DOPED SB(2)TE3 SINGLE-CRYSTALS

The reflectance and the transmittance spectra in the IR region are measured on Ti-doped Sb2Te3 single crystal samples grown by a modified Bridgman technique. The plasma resonance frequency, the optical relaxation time, and the high-frequency dielectric constant are determined by fitting the Drude-Zener formulas to the reflectance spectra. It is found that Ti impurities in Sb2Te3 behave as donors. The transmittance spectra are used for the determination of the dependence of the absorption coefficient K on the energy of incident photons. The optical width of the energy gap is found to decrease with increasing Ti content. The values of the exponent oc from the relation of K similar to lambda(x) for the long-wavelength absorption edge range within the interval of 1.8 to 2.2, i.e. the dominant scattering mechanism of free current carriers in Sb2Te3 crystals doped with Ti atoms is the scattering by acoustic phonons.