Epitaxy is growth of a crystalline layer with an orientation relationship to a crystalline substrate. Homoepitaxy uses the same material; heteroepitaxy uses a different one. A substrate can guide atomic ordering, but a mismatch of lattice parameters introduces strain and can eventually produce misfit dislocations. Thus an apparently flat film need not be strain-free or defect-free. Molecular beam epitaxy controls incident material fluxes in vacuum, while other epitaxial methods use reactive vapors or liquids. The orientation relationship, layer thickness and strain state are distinct parts of the description.
Heteroepitaxy is epitaxy in which a crystalline film grows on a different material while maintaining an orientation relationship with the substrate. For example, a semiconductor layer can be grown on a different crystalline semiconductor to combine useful electronic properties.
A simple mismatch measure is , where and are the relaxed film and substrate lattice parameters. A coherent layer can accommodate mismatch through elastic strain; increasing thickness increases the stored elastic energy and can favour relaxation through dislocations. Orientation, chemical compatibility and strain relaxation are therefore separate questions. An ordered epitaxial film need not retain the lattice parameter it would have in an unconstrained bulk crystal.
Homoepitaxy is epitaxy in which the deposited crystalline material is the same material as its crystalline substrate. Growing silicon on a silicon wafer is a standard example. The substrate supplies an orientation template, allowing the new layer to continue the crystal's ordering.
Using the same material does not require identical impurity concentrations or electrical properties. Controlled semiconductor doping can create a layer with a different carrier concentration while retaining the same host crystal structure. Surface preparation, contamination and growth conditions still control defects and interfaces. Homoepitaxy is therefore useful for separating control of crystalline orientation from control of a device layer's composition and electronic behaviour.
Epitaxial growth using volatile metal-organic precursors delivered in the gas phase. Precursor decomposition and surface incorporation grow a crystalline compound layer or nanostructure; temperature and mass transport influence composition.
Epitaxial crystal growth confined to exposed substrate regions defined by a growth-inhibiting mask. Pattern position and pitch can control wire nucleation, while transport and facet-dependent incorporation influence growth rate and composition.
Molecular beam epitaxy grows crystalline films by directing controlled beams of material toward a crystalline substrate in a vacuum system. A typical apparatus has source cells, shutters, a heated substrate holder and diagnostic tools such as electron diffraction. Opening or closing shutters changes which species reach the surface, enabling layered heterostructures. Growth quality depends on surface diffusion, incorporation and desorption as well as the arriving flux. The method's value is precise control of composition and interfaces; depositing material in vacuum alone does not ensure epitaxial crystal ordering.
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Epitaxy is a process used in material science and semiconductor manufacturing where a thin layer of crystalline material is grown on a substrate of a different material. The key characteristic of epitaxy is that the new layer, or epitaxial layer, is crystallographically aligned with the underlying substrate. This alignment is critical for applications in electronics and optics, as it can influence the electrical, optical, and mechanical properties of the resulting material.