Epitaxial wafer

rdf:langString Epitaxial wafer

rdf:langString January 2017

rdf:langString There exist more applications than mentioned yet

rdf:langString An epitaxial wafer (also called epi wafer, epi-wafer, or epiwafer) is a wafer of semiconducting material made by epitaxial growth (epitaxy) for use in photonics, microelectronics, spintronics, or photovoltaics. The epi layer may be the same material as the substrate, typically monocrystaline silicon, or it may be a more exotic material with specific desirable qualities. Silicon epi wafers were first developed around 1966, and achieved commercial acceptance by the early 1980s. Methods for growing the epitaxial layer on monocrystalline silicon or other wafers include: various types of chemical vapor deposition (CVD) classified as Atmospheric pressure CVD (APCVD) or metal organic chemical vapor deposition (MOCVD), as well as molecular beam epitaxy (MBE). Two "kerfless" methods (without abrasive sawing) for separating the epitaxial layer from the substrate are called "implant-cleave" and "stress liftoff". A method applicable when the epi-layer and substrate are the same material employs ion implantation to deposit a thin layer of crystal impurity atoms and resulting mechanical stress at the precise depth of the intended epi layer thickness. The induced localized stress provide a controlled path for crack propagation in the following cleavage step. In the dry stress lift-off process applicable when the epi-layer and substrate are suitably different materials, a controlled crack is driven by a temperature change at the epi/wafer interface purely by the thermal stresses due to the mismatch in thermal expansion between the epi layer and substrate, without the necessity for any external mechanical force or tool to aid crack propagation. It was reported that this process yields single atomic plane cleavage, reducing the need for post lift-off polishing, and allowing multiple reuses of the substrate up to 10 times. The epitaxial layers may consist of compounds with particular desirable features such as gallium nitride (GaN), gallium arsenide (GaAs), or some combination of the elements gallium, indium, aluminum, nitrogen, phosphorus or arsenic.