Electron-phonon interaction effects on surface states of polar crystals

A variational approach is used to study the surface states of polarons in a semi-infinite polar crystals. The surface-state energy of an electron is calculated, by including the effect of the electron surface-optical phonon interaction. The numerical results for the energies of the surface-states of the polarons in several I-VII II-VI and III-V compound crystals are obtained and discussed. It is found that the variational results for the surface-state levels are lower than those obtained via the previous near-free-electron approximation perturbation method. The electron-phonon coupling lowers the surface-state energy levels and cannot be neglected, especially for materials with strong electron-phonon-coupling and broad band gaps.