A method of growing a thin layer of material upon a single-crystal substrate, such as silicon, so that the crystal structure of the layer is identical to that of the substrate. The material, which may be the same as the substrate or a different one, is usually deposited from a gaseous mixture (see vapour phase epitaxy). The technique is extensively used in semiconductor technology when a layer (the epitaxial layer) of different conductivity to the substrate is required. See also liquid phase epitaxy; molecular beam epitaxy.