The Crystal Binding Energies of the IV–VI Semiconductors

It is shown that the crystal binding energies of the IV–VI narrow gap semiconductors are calculated using the Heitler-London-Löwdin treatment modified so as to include the effect of covalent binding. The numerical calculations performed for PbS show that the calculated crystal binding energy, which is in good agreement with observation, consists of two parts, namely the binding energy in ionic approximation and the covalent binding correction and the former is almost equal to the one obtained by the classical Born-Mayer-Sherman treatment. The covalent bonding correction for PbS, PbSe, PbTe, SnTe, and GeTe are found to be 2.1, 2.9, 3.3, 3.2, and 3.9 eV/molecule, respectively.