Theoretical study of deep-defect states in bulk PbTe and in thin films

The nature of neutral defect states in PbTe, a narrow band-gap semiconductor, has been studied using density functional theory and supercell models. We find that the defect states associated with different substitutional impurities and native point defects found in bulk PbTe are preserved in the film geometry, but get modified as one goes from the surface to the subsurface layers and then to the bulklike layers. These modifications, which usually occur in the neighborhood of the band gap, will impact the transport properties of the films. Energetic studies of different impurities and native defects embedded in bulk PbTe and in different layers of PbTe films show different energy landscapes, depending on the nature of the defects. This has important implications in doping mechanism and the distribution of the defects in bulk PbTe with grain boundaries and in PbTe nano- structures. Available experimental data are discussed in the light of our theoretical results. Our results in pure PbTe001 films are consistent with earlier works and with experiment.