Electronic and Vibrational Properties · 188.8.131.52 Theory
This chapter describes theory of electronic structure of surfaces for semiconductors. The theoretical determination of distribution of filled and empty surface states through the calculation of quantities like the local density of states (LDOS) and the surface band structure is of great avail in the understanding of the spectra, since it allows the comparison between momentum-dependent spectra and the measured band dispersion and the evaluation of the relative intensities and the lineshapes of the peaks. From a theoretical viewpoint the presence of a surface implies two main difficulties: a) the translational symmetry perpendicular to the surface is broken, b) the atomic geometry, i.e. the positions of the atoms at the surface or in the outermost planes, is not the same as in the bulk. In principle the best way of dealing with the problem of the atomic geometry is to determine a stable structure by an energy minimization procedure. The expected behavior of surface states and resonance are illustrated. A typical example for the ideal Si( 111) surface is presented. Charge density behaviour for typical surface states of the ideal surfaces of semiconductors are also illustrated.