Charge-carrier density collapse in layered crystals of the family [(Ge,Sn,Pb)(Te,Se)]m[(Bi,Sb)2(Te,Se)3]n (m, n = 0, 1, 2…)

Abstract

The causes of the “charge-carrier density collapse”, i.e., a sharp increase in the equilibrium charge-carrier density n, p = 1 × 10¹⁹ → (2–5) × 10²⁰ cm^–3 in going from binary alloys such as GeTe and Bi₂Te₃ to the family of ternary alloys [(Ge,Sn,Pb)(Te,Se)]_m[(Bi,Sb)₂(Te,Se)₃]_n [m, n = 0, 1, 2…) are discussed. The phenomenon is associated with the positional disordering of heterovalent cations (Ge⁺², Sn⁺², Pb⁺² ↔ Bi⁺³, Sb⁺³) in the cation sublattice of ternary alloys. The phenomenon is not observed during the disordering of isovalent cations (Bi⁺³ ↔ Sb⁺³) or anions (Te^–2 ↔ Se^–2).