Core electron binding energy shifts and screening in tetrahedral semiconductors

Abstract

Tight-binding heterojunction band offset calculations are brought into conceptual agreement with natural band lineup models by redefining the average hybrid energy to be the common reference level in each semiconductor. The self-consistent calculation of charge redistribution in semiconductor bonds in the presence of a substitutional impurity, using tight-binding theory based upon universal parameters with the inclusion of coulomb interactions, is extended to include the case of polar semiconductors. The core-to-valence-band maximum binding energy shifts in semiconductor alloys are then obtained using the results of this calculation. It is found that, in general, these shifts do not coincide with heterojunction band offsets as would be suggested by a natural band lineup approach. Differences in the two values occur as a result of lattice mismatch and/or a disparity in the hybrid energies. However, in the case of the cadmium telluride/mercury telluride and aluminum arsenide/gallium arsenide systems, where the mismatches and hybrid energy differences are small, the two values are found to be nearly the same, in agreement with experiment. These results suggest a limited applicability of models which neglect charge redistribution.