The structure, chemistry, and spectroscopy of the surfaces of tetrahedrally coordinated semiconductors

Abstract

The proper description of the electron physics and chemistry of the terminating surface of a solid lies somewhere between the collective approach successful in the description of infinite lattices and the local approach successful in the description of small molecules. When viewed in the collective approach as the terminating atomic layer of an otherwise perfect, semi-infinite solid, the collective approach treats the surface as a boundary condition on the delocalized wave functions describing the valence and excited states of the solid. An accurate description would require detailed knowledge of the atomic arrangement in the surface region, the so–called selvage structure, from which the lattice potential or the appropriate boundary conditions can be quantitatively established. With this information, the lattice wave functions and their eigenvalues can be obtained, in principle, and it then remains to be seen, depending on the details of the selvage structure, whether localized states and/or scattering resonances appear owing t o the presence of the surface. Alternatively, when viewed in the local approach as the first layer of atoms of a solid where gas phase atoms and molecules encounter the solid, the local approach treats the surface as a collection of atoms with a given local bonding coordination to their nearest neighbors in the lattice and with certain chemical activity towards atoms impinging on the surface from the gas phase. Here too, an accurate description would require a detailed knowledge of the selvage structure (local coordination) from which the character of the bonding orbitals available for reactivity can be assessed. As the former approach is that of the physicist and the latter that of the chemist, it is not surprising the surface science has brought these two disciplines into intimate and interactive collaboration.