Epitaxy
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Epitaxy is the growth of crystals of one material on the crystal face of another material, such that the crystalline substrates of both materials have the same structural orientation. Epitaxy can be classified into homoepitaxy, in which the two materials are the same, and heteroepitaxy, in which they are different.
Common use in industry is the growth of additional layers of doped silicon on the polished sides of prime silicon wafers, before they are processed into semiconductor devices. This is typical of the power devices, such as those used in pacemakers, vending machine controllers, automobile computers, etc.
Commonly, this is accomplished by either single or batch wafer processing using Chemical vapor deposition in an epitaxial reactor, which heats the wafers, etches the exposed face with hydrochloric gas, and then grows the epitaxial layers by flowing a gas mixture that contains silicon and a dopant over the wafer which is so hot that it glows. The gaseous molecules deposit on the face, if done properly, and extend the crystalline structure.
Manufacturing issues include control of the amount and uniformity of the deposition's resistivity and thickness, the cleanliness and purity of the surface and the chamber atmosphere, the prevention of the typically much more highly doped substrate wafer's outgassing of dopant to the new layers, imperfections of the growth process, and protecting the surfaces during the manufacture and handling.
Alternatively, molecular beam epitaxy is used.