A theory of surface and interface electronic properties of crystalline solids: Applications to 2-6 compounds

The surface and interface properties of HgTe and CdTe are studied with the hope of understanding the underlying properties of superlattices as well as the surface characteristics of these compounds. A Green's function (GF) model of the surface and interface systems was employed. The GF of a semi-infinite system is described in terms of the GF derived from the Hamiltonian of the infinite crystal into two semi-infinite crystals in some crystallographic direction. Subsequently the GF of the interface of two crystals is determined by the GF's of the individual semi-infinite systems and the scattering potential describing the coupling between the two crystals. Model calculations of the surface and interface electronic properties of three-dimensional two-band crystals were performed. The bulk states are modified, and under certain conditions localized surface or interface bands are found to occur inside the band gap. The local densities of states of the pure HgTe and CdTe surfaces and interfaces at the important T and J points in the surface Brillouin zone were examined. Numerical calculations were performed for (100) planes where the lattice is composed of alternating layers of anions (TE) and cations (Cd, Hg). The surface or resonance states on the cation terminated (100) surface and CdTe and the anion terminated (100) surface of HgTe were observed even for plain unperturbed surfaces. The energies and strengths of the surface states were found to change under the influence of surface perturbations.