Interface-bond-polarity model for semiconductor heterojunction band offsets

A simple model is presented for the calculation of heterojunction band offsets, called the interface-bond-polarity model. The model is based on the self-consistent-dipole theory presented in the preceding paper. According to this theory the interface dipole resulting from the charge transfer at the interface can be obtained by screening the initially induced dipole by the macroscopic dielectric constant of the heterojunction interface region given approximately by the harmonic average of the dielectric constants of the two semiconductors. The present paper presents a simple model for calculating the initially induced dipole from the charge transfers that occur in individual interface bonds when the two semiconductors are brought into contact. These are described in terms of the polarities of these bonds. A new polarity scale is developed on the basis of the ${\mathrm{sp}}^3$-bond-orbital model parametrized by means of a tight-binding and minimal-basis-set version of the linear-muffin-tin-orbital method. An extensive list of bond polarities, including those of interfacial bonds, is provided, in addition to the reference valence-band levels on the atomic-sphere-approximation scale. The band offset for two interface orientations and various bonding configurations are considered. These are given as simple analytic expressions, which are easily evaluated with the help of the tables. This is illustrated with various examples, including polar as well as nonpolar interfaces. There are no adjustable parameters in the model.