Epitaxiás

Epitaxiás, often rendered in English as epitaxy, is a process in materials science and solid-state physics in which a crystalline film is grown on a crystalline substrate in an ordered manner that preserves a specific orientation relationship with the substrate. The term derives from the Greek epi-, meaning upon, and taxis, meaning arrangement or order.

In homoepitaxy, the film material is the same as the substrate; in heteroepitaxy, the film material is different. Epitaxial growth is typically performed under controlled environments using methods such as molecular beam epitaxy (MBE), chemical vapor deposition (CVD), or metalorganic chemical vapor deposition (MOCVD). Other related techniques, including pulsed laser deposition and sputtering, can also produce epitaxial layers under suitable conditions.

A central consideration in epitaxy is lattice matching. A small lattice mismatch between film and substrate enables coherent growth with low defect density, while larger mismatches can cause strain, dislocations, and surface roughening. The concept of critical thickness describes the maximum film thickness that can be grown epitaxially without relaxation. Temperature, surface preparation, and impurities influence layer quality, dopant incorporation, and interface sharpness.

Applications span semiconductor devices and optoelectronics. Epitaxial layers are foundational for high-quality GaAs or GaN layers used in LEDs, lasers, and high-electron-mobility transistors, as well as silicon- or III–V-based devices. Epitaxy also enables quantum wells, superlattices, and tailored electronic or optical properties through controlled composition and strain.

Characterization techniques such as X-ray diffraction, reflection high-energy electron diffraction, and transmission electron microscopy assess crystalline quality, orientation, and interface sharpness, supporting optimization of epitaxial growth processes.