Source:http://www.siliconfareast.com/epitaxy.htm#1.Epitaxy or epitaxial growth is the process of depositing a thin layer (0.5 to 20 microns) of single crystal material over a single crystal substrate, usually through chemical vapor deposition (CVD). In semiconductors, the deposited film is often the same material as the substrate, and the process is known as homoepitaxy, or simply, epi. An example of this is silicon deposition over a silicon substrate. Silicon epitaxy is done to improve the performance of bipolar devices. By growing a lightly doped epi layer over a heavily-doped silicon substrate, a higher breakdown voltage across the collector-substrate junction is achieved while maintaining low collector resistance. Lower collector resistance allows a higher operating speed with the same current. Epitaxy has also recently been used in CMOS VLSI circuits. By fabricating the CMOS device on a very thin (3-7 microns) lightly doped epi layer grown over a heavily-doped substrate, latch..