Abstract:
The spectra of optical absorption in multicomponent $n$- and $p$-type solid solutions based on bismuth and antimony chalcogenides with substitutions in both sublattices of Bi$_2$Te$_3$ have been investigated. It has been found that, in all the solid solutions studied, just as in the parent compound Bi$_2$Te$_3$, direct allowed transitions occur at the interband absorption edge at $T$ = 300 K. The band gap $E_g$ in the $n$-Bi$_{2-x}$Sb$_x$Te$_{3-y-z}$Se$_y$S$_z$ solid solutions weakly increases with increasing number of substituted atoms in the Bi and Te sublattices. These atomic substitutions do not leads to an increase in $E_g$ as compared to that of the $n$-Bi$_2$Te$_{2.7}$Se$_{0.3}$ composition. An analysis of the optical absorption spectra suggests that the solid solutions under consideration are weakly degenerate, a conclusion supported by the earlier studies of the thermoelectric and galvanomagnetic properties. It has been established that, in the conduction band of the Bi$_{1.8}$Sb$_{0.2}$Te$_{2.7}$Se$_{0.15}$S$_{0.15}$ solid solution, there is an additional extremum lying above the main extremum at a distance no more than 0.1 eV.
Fulltext:
PDF file (257 kB)
