Defects III surfaces and interfaces

Two-dimensional defects in crystals consist of planes of atomic sites where the solid terminates or meets a plane of another crystal. We refer to the first type of defects as surfaces, to the second as interfaces. Interfaces can occur between two entirely different solids or between two grains of the same crystal, in which case they are called grain boundaries. 

Surfaces are the subject of a very broad and rich field of study called surface science, to which entire research journals are devoted (including Surface Science and Surface Review and Letters). It would not be possible to cover all the interesting 

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Bulk point defects have a considerable importance in III-V semiconductors such as gallium arsenide GaAs, because they interact with free carriers, acting as scattering centers, traps and recombination centers, and have a large effect on electronic transport, even at very low concentration. Surface and interface defects due to processing are also important. 

There are different criterion of how to classify solid-solid interfaces. One is the sharpness of the boundary. It could be abrupt on an atomic scale as, for example, in III-IV semiconductor heterostructures prepared by molecular beam epitaxy. In contrast, interdiffusion can create broad transitions. Surface reactions can lead to the formation of a thin layer of a new compound. The interfacial structure and composition will therefore depend on temperature, diffusion coefficient, miscibility, and reactivity of the components. Another criterion is the crystallinity of the interface. The interface may be crystalline-crystalline, crystalline-amorphous, or completely amorphous. Even when both solids are crystalline, the interface may be disturbed and exhibit a high density of defects. 

Thermal oxidation of OaAs for example produces a gallium rich oxide. In a number of studies, it has been shown that the oxide on GaAs contains Ga O and GajOg (see figure 6) and As is peaked at the interface. By preferential oxidation of one component of the compound semiconductor, defects are produced at the interface. Again this produces a barrier height equal to that observed for most of the metals evaporated on the GaAs surface (10). This accounts for the unsuccessful attempts to make metal oxide semiconductor structures by intrinsic III-V oxidation. 

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