epitaxie

Epitaxy refers to a deposition process in which a crystalline overlayer is grown on a crystalline substrate in such a way that the overlayer adopts a specific crystallographic orientation with respect to the substrate. The term is derived from Greek epi-, “upon,” and taxis, “order.” Epitaxial growth results in well-ordered heterostructures and is widely used in semiconductor device fabrication and materials science.

There are two main categories: homoepitaxy, where the deposited layer is the same material as the substrate (for example GaAs on GaAs); and heteroepitaxy, where the layer is a different material (for example GaAs on Si). The lattice mismatch between substrate and film governs strain, defect formation and the achievable thickness.

Common epitaxial techniques include molecular beam epitaxy (MBE), where atomic beams are directed at the heated substrate under ultra-high vacuum; and chemical vapor deposition (CVD), including metal-organic CVD (MOVPE or MOCVD) and hydride vapor phase epitaxy (HVPE). These methods differ in precursors, growth rates, and temperature ranges; they all aim to preserve crystalline order during deposition.

Growth modes describe how films form: Frank–van der Merwe (layer-by-layer), Volmer–Weber (island growth), and Stranski–Krastanov (layer-plus-islands). Lattice matching, surface preparation, substrate miscut, and temperature affect epitaxy. Strain can be accommodated elastically up to a critical thickness, above which dislocations form and degrade material quality.

Applications include semiconductor heterostructures such as quantum wells and superlattices, optoelectronic devices (LEDs, laser diodes), high-electron-mobility transistors, solar cells, and advanced sensors. Epitaxial films enable precise control of composition, doping, and strain, which influence electronic and optical properties.