Epitaxial interfaces in solids are a special class of crystalline interfaces where the molecular arrangement of one crystal on top of another is defined by the crystallographic and chemical features of the underlying crystal. The term “epitaxy” was introduced to describe the importance of having parallelism between two lattice planes with similar networks of closely similar spacing. Epitaxial phenomena are important to study and understand, as they occur widely in nature (such as oxidation) and are the foundation by which modern semiconductor devices are grown and fabricated.
Epitaxial interfaces are a subset of a class of interfaces where lattice planes achieve a correspondence across an interface. If the matching is not perfect, such a correspondence can be achieved by a number of ways, including dilation and contraction of lattice planes; rotation of overgrowth (epilayer relative to the orientation of the substrate) until a set of closely matched lattice spacing can be found; and tilting of the epilayer with respect to the substrate (see illustration).
The extent to which epitaxial films are mechanically stable due to coherency stresses is governed not only by the extent of lattice misfit but also by the strength of the chemical bond between the epilayer and the substrate. This property of adhesion is manifested by the extent to which the overlayer wets the substrate. Extremely thin layers that are only a few atoms thick can be produced. Such thin layers form the microstructural foundation for the fabrication of quantum wells, which are extremely important in semiconductor device applications. See Quantized electronic structure (QUEST)