Heterostructure and Quantum Well Physics

Heterostructures are the building blocks of the most advanced semiconductor devices being developed and produced. They are essential elements of the highest-performance optical sources and detectors, and are being employed in high-speed and high-frequency digital and analog devices. The use of heterostructures is that they offer precise control over the states and motions of charge carriers in semiconductors. A heterostructure is defined as a semiconductor structure in which the chemical composition changes with position. The simplest heterostructure consists of a single heterojunction, which is an interface within a semiconductor crystal across which the chemical composition changes. Most devices and experimental samples contain more than one heterojunction. Closely matching the lattice constants of the participating semiconductors—good lattice matching—is a necessary condition for the fabrication of high-quality heterojunctions. Heterostructures are fabricated by an epitaxial growth process. Most of the established epitaxial techniques have been applied to the growth of heterostructures. These include molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD). Liquid phase epitaxy (LPE) is an older heterostructure technology, which has been supplanted by MBE and MOCVD because it does not permit as precise control of the fabricated structure.