Molecular Beam Epitaxy (MBE)

Crystalline semiconductors are grown by raising the temperature to allow more surface migration and by using a crystalline substrate such as Si, GaAs, InP wafer, etc. Epitaxial growth is primarily used for II-VI, and III -V semiconductors, special metallic oxides and metals. MBE dominates III -V electronic market and strong competitor in upper end LASER market. In an UHV (ultra high vacuum) chamber, ultra high purity materials are evaporated. Because of the very low pressure, the mean free path is very long, typically hundreds of meters. Thus, the evaporated material travels in a straight line toward a hot substrate. After reaching the substrate, the atom or molecule moves around until it finds an atomic site to chemically bond to. Shutters can be used to turn the beam flux on and off. The flux of atoms/molecules is controlled by the temperature of the evaporation source/cell. Due to ultra high vacuum conditions, MBE offers the highest purity depositions. By this method, almost any fraction of an atomic layer can be deposited and layers can be sequenced one layer at a time; for example Ga then As then Ga etc.