Epitaksial

Epitaksial, also spelled epitaxial, describes the growth of a crystalline layer on a crystalline substrate in which the film lattice aligns with that of the substrate. The orientation relationship is governed by lattice matching and surface energetics.

There are two main types: homoepitaxy and heteroepitaxy. Homoepitaxy uses the same material for film and substrate, while heteroepitaxy uses different materials, which introduces lattice mismatch, strain, and the potential for defects. The degree of alignment is characterized by an epitaxial relationship between the film and substrate, often described by crystallographic orientations.

Growth modes include Frank–van der Merwe (layer-by-layer), Volmer–Weber (island growth), and Stranski–Krastanov (layer-plus-island), depending on surface energies and interactions. These modes influence film smoothness, roughness, and defect formation. Strain from lattice mismatch affects the critical thickness at which relaxation occurs and can lead to misfit dislocations.

Common methods for epitaxial growth are molecular beam epitaxy (MBE) and chemical vapor deposition (CVD), including metal-organic CVD (MOCVD or MOVPE). Other vapor-phase epitaxy techniques are used for various materials. Substrates are prepared to be clean, often with buffer layers to reduce defects. Growth parameters such as temperature, pressure, and material flux are carefully controlled to influence crystallinity and interface quality.

Applications span semiconductor devices and optoelectronics, including silicon, GaAs, and GaN-based structures; LEDs and lasers; high-electron-mobility transistors; and oxide or perovskite thin films in photovoltaics and sensors. Epitaxial films enable precise crystallography, well-defined interfaces, and engineered strain essential to device performance.