BONDING AT SEMICONDUCTOR INTERFACES

In contrast to simple metals, semiconductors have to be viewed as molecular networks with valence electrons strongly concentrated near atoms and along bonds. Disturbing these networks results (with increasing perturbation strength) in bending, stretching and breaking of the bonds. This simple picture has to be augmented by intermediate situations, such as the formation of new types of bonds which can stabilize configurations with changed atomic coordination numbers. Typically, the energy required to completely break a semiconductor bond is ~1 eV/atom. Large elastic distortions can therefore be accommodated to avoid breaking of bonds or to favor the formation of new types of weaker bonds. A beautiful example of this behavior is the formation of π-bonds in order to stabilize the Si(111) (2x1) surface1. Similar situations can be expected for internal interfaces and grain boundaries