Free current carrier concentration and point defects in Bi2-xSbxSe3 crystals

From IR reflectivity spectra measurement on natural (0001) cleavage planes of Bi2-xSbxSe3 single crystals (space group D-3d(5)-R3m), values of plasma resonance frequency omega(p) were determined. Using the model respecting the existence of light and heavy electrons the dependence of free current carriers concentration on Sb-atom content in Bi2-xSbxSe3 single crystals (for x = 0.0 - 0.4) was obtained. There is a maximum in this dependence at lower Sb concentration (x congruent to 0.024). This effect is explained by a model of point defects, where both the concentration of negatively charged native defects in a Bi2Se3 lattice (anti-site defect Bi'(Se), seven-layer lamellae Bi3Se4-) and the concentration of vacancies in a selenium sublattice (V-Se(..)) decreases with Sb content. On this basis the observed rise of the Hall mobility R(H)sigma in the range from 500 to 1200 cm(2)/Vs is explained. (C) 2002 Elsevier Science (USA).