Electronic structure of defects and defect clusters in narrow band-gap semiconductor PbTe

Lead chalcogenide salts PbSe and PbTe are IV-VI narrow gap semiconductors whose study over last several decades has been motivated by their importance in infrared detectors, lasers and thermoelectrics. Recently a class of systems, AgSbPb2n-2Ten, has been found to be excellent high temperature thermoelectrics. Since electronic properties of semiconductors in general and thermoelectric behaviour in particular, are dominated by defects, we have carried out ab initio electronic structure calculations of Ag and Sb substitutional defects in PbTe. We find that these defects give rise to deep defect states and the electronic structure near the gap depends sensitively on the micro structural arrangements of these defects. The modified electronic structure may be responsible for the observed high temperature thermoelectric properties of the above compounds.