epitaxially

Epitaxially is an adverb used to describe the growth of a crystalline layer on a crystalline substrate in which the deposited film adopts an ordered orientation that mirrors the substrate’s lattice. The underlying process, epitaxy, aims to produce a continuous, single-crystal film with a defined crystallographic relationship to the substrate.

During epitaxial growth, the deposited material nucleates and extends with a specific orientation, so that the film lattice is aligned with the substrate lattice. When the film and substrate are the same material, the process is called homoepitaxy; when they differ, it is heteroepitaxy.

The quality of epitaxial layers depends on lattice match, surface cleanliness, and thermal compatibility. Lattice misfit can induce strain and, beyond a critical thickness, misfit dislocations. Epitaxial growth can proceed in different modes: layer-by-layer (Frank-van der Merwe), layer-plus-islands (Stranski-Krastanov), or island growth (Volmer-Weber).

Common methods to achieve epitaxy include molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), and other chemical vapor deposition techniques. Epitaxial films are widely used to create semiconductor heterostructures and quantum wells, such as silicon on silicon (homoepitaxy) or GaAs on GaAs, and in heteroepitaxy like GaAs on silicon or GaN on sapphire.

Applications span integrated circuits, optoelectronic devices, and high-performance transistors. Epitaxially grown layers enable precise control of composition, doping, and strain, which tailor electronic and optical properties. Challenges include managing lattice mismatch, thermal expansion differences, and defect densities.