Ab Initio Study of Deep Defect States in Narrow Band-Gap Semiconductors: Group III Impurities in PbTe

The nature of deep defect states, in general, and those associated with group III elements (Ga, In, Tl) in narrow band-gap IV–VI semiconductors (PbTe and PbSe), in particular, have been of great interest over the past three decades. We present ab initio electronic structure calculations that give a new picture of these states compared to the currently accepted model in terms of a negative-$U$ Hubbard model. The Fermi surface pinning and why In-doped PbTe and related compounds show excellent high temperature thermoelectric behavior can be understood within the new picture.

Figure 1

(a) Total DOS of ${\mathrm{Pb}}_{32}{\mathrm{Te}}_{32}$ and ${\mathrm{InPb}}_{31}{\mathrm{Te}}_{32}$ and (b) their difference $\Delta {\rho }_{\mathrm{tot}}$, (c) partial DOS associated with nearest neighbor Te atoms of the In impurity, and (d) In partial DOS of $s$ character. Results obtained in FPLAPW calculations. The Fermi level is at 0 eV.

Figure 2

Total DOS of (a) ${\mathrm{InPb}}_{31}{\mathrm{Te}}_{32}$ with SOI (with ionic relaxation) and without SOI (with and without ionic relaxation), and (b) ${\mathrm{InPb}}_{31}{\mathrm{Te}}_{32}$ and ${\mathrm{InPb}}_{107}{\mathrm{Te}}_{108}$ (without ionic relaxation, without SOI). Results obtained in PAW calculations. The Fermi level is at 0 eV.