Abstract
Spectra of optical absorption in Bi 0.5 Sb 1.5 Te 3 films grown on mica and KBr substrates have been investigated for T = 145 and 300 K. The data obtained have been analyzed together with the data of investigations on the fundamental absorption edge for Bi 2 Te 3 available in the scientific literature. It has been revealed that the interband absorption spectra for both Bi 0.5 Sb 1.5 Te 3 and Bi 2 Te 3 represent a superposition of two components corresponding to direct and indirect allowed optical transitions. In this case, the least energy gap separating the valence band and the conduction band is direct for Bi 2−x Sb x Te 3 (x ≤ 1.5, T = 300 K). For Bi 0.5 Sb 1.5 Te 3 the temperature variation rates have been estimated for the thresholds of direct and indirect interband transitions. It has been shown that this solid solution is direct gap solution at T ≥ 145 K.
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