Structure of DX-like centers in narrow-band IV–VI semiconductors doped with group-III elements

Abstract

This paper presents a study of the structure of the IR reflectance spectra in the sub-gap region of lead telluride doped with indium and gallium and the Raman spectra in PbTe(In). In the Raman and reflectance spectra of PbTe(In), features are observed at a frequency of ω 0⋍120 cm−1, whose amplitude sharply increases at temperatures T below the temperature where delayed photoconductivity appears, T c⋍25 K. A similar feature at a frequency of ω 0⋍155 cm−1 is also observed in PbTe(Ga), with the amplitude of the feature sharply increasing for T>T c⋍80 K. An analysis of the resulting data makes it possible to conclude that, in contrast with classical DX centers in III–V semiconductors, the microscopic structure of the impurity centers in the two-electron (DX-like) ground state does not correspond to an impurity atom shifted from a lattice site, whereas the impurity atom is shifted from a lattice site for the metastable one-electron impurity state.