Plasma screening of the fundamental absorption edge in crystals of Bi2Te3-Sb2Te3 solid solutions with more than 80 mol % Sb2Te3

The regularities of changes in the optical properties of crystals of Bi₂Te₃-Sb₂Te₃ solid solutions in the range of the effects caused by free-carrier plasma oscillations at a variation in the ratio of Bi₂Te₃ and Sb₂Te₃ components are investigated. It is established that, when the Sb₂Te₃ content in a solid solution exceeds 80 mol %, the fundamental absorption edge undergoes plasma screening. Doping a Sb₂Te₃ crystal with tin increases the free-carrier concentration and plasma frequencies, thus enhancing the screening effect, whereas introduction of 0.1 mol % selenium reduced the plasma frequency and thus removes the fundamental-absorption-edge screening.