Structural and electronic properties of Pb1−xCdxTe and Pb1−xMnxTe ternary alloys

Abstract

A systematic theoretical study of two PbTe-based ternary alloys, Pb${}_{1\ensuremath{-}x}$Cd${}_{x}$Te and Pb${}_{1\ensuremath{-}x}$Mn${}_{x}$Te, is reported. First, using ab initio methods, we study the stability of the crystal structure of CdTe-PbTe solid solutions, to predict the composition for which the rock-salt structure of PbTe changes into the zinc-blende structure of CdTe. The dependence of the lattice parameter on Cd (Mn) content $x$ in the mixed crystals is studied by the same methods. The obtained decrease of the lattice constant with $x$ agrees with what is observed in both alloys. The band structures of PbTe-based ternary compounds are calculated within a tight-binding approach. To describe correctly the constituent materials, tight-binding parametrizations for PbTe and MnTe bulk crystals as well as a tight-binding description of rock-salt CdTe are proposed. For both studied ternary alloys, the calculated band gap in the L point increases with $x$, in qualitative agreement with photoluminescence measurements in the infrared. The results show also that in p-type Pb${}_{1\ensuremath{-}x}$Cd${}_{x}$Te and Pb${}_{1\ensuremath{-}x}$Mn${}_{x}$Te mixed crystals an enhancement of thermoelectrical power can be expected.