epilayer

An epilayer, short for epitaxial layer, is a crystalline layer grown on a crystalline substrate in which the layer adopts the same or a defined crystallographic orientation as the substrate. Epitaxial growth is used to produce high-quality single-crystal films with controlled composition and thickness. It is classified as homoepitaxy when the epilayer and substrate are the same material, and heteroepitaxy when they differ.

Common growth methods include molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD, also called MOVPE), and chemical vapor deposition (CVD). Growth conditions such as substrate temperature, pressure, and precursor flux govern adatom mobility, incorporation, and defect formation. Lattice matching between epilayer and substrate minimizes strain; deliberate mismatch can induce strain or form quantum structures.

Silicon, GaAs, GaN, InP, and SiC are frequently grown epitaxially on Si, GaAs, sapphire, or SiC substrates. Heteroepitaxy enables integration of materials with different properties, while homoepitaxy is used to improve purity and reduce defects. Epilayers are essential for devices such as LEDs, laser diodes, high-speed transistors, and solar cells.

Quality of the epilayer, including surface morphology and defect density (e.g., threading dislocations), strongly influences device performance. Strain management, buffer layers, and post-growth annealing are commonly employed. Epitaxial layers can be engineered into quantum wells, superlattices, or strained layers for bandgap and mobility control.

Characterization techniques include X-ray diffraction, RHEED, TEM, and atomic force microscopy. In situ monitoring and ex situ analysis help assess thickness, composition, and crystalline quality during and after growth.