Dan Maser Also known as “carborundum” Occurs naturally (although very rare) as moissanite While rare naturally on Earth, common form of stardust First synthetically created in 1893 Initially used as an abrasive moissanite Used as a detector in early radios 1907 - First LED Semiconductor Can be doped n-type with N, P p-type with Al, B, Ga, Be B substitutes C, while Al substitutes Si (produce different type semiconductors) SiC monocrystal 250 crystalline forms! Three most common polytypes: (α) 6H-SiC (hexagonal), (β) 3C-SiC (lone cubic), and 4HSiC (hexagonal) α-SiC is the most common Pure SiC is colorless – black color comes from Fe impurities, rainbow shine is from a passivation layer of SiO2 (α) 6H-SiC (β) 3C-SiC 4H-SiC G. Pensl and W. J. Choyke Comparison of n-type CVD film grown on the C-face of 6H-SiC to p-type CVD film grown on Si-face of 6H-SiC Both samples show ZPL’s P0, R0, S0 characteristic of N-doped 6H-SiC Come from recombination radiation of exciton (hole-electron pair) in a four-particle neutral donor complex at three inequivalent donor sites In C-face film, prominent features below ZPL are phonon replicas of P center Indicates strong N-doping In Si-face spectrum, three features denoted 4A, I, A0 4A – acceptor four-particle neutral complex A0 associated with Ti in 6H-SiC Comparison of photoluminescence spectra (410-434 nm) In C-face, lines due to two phonon replicas of the P line Combinations of the P line phonon replicas and a center of the zone TO phonon are seen In Si-face, ZPL of Ti center, A0, B0, C0, and phonon replicas are marked Comparison of photoluminescence spectra (430 nm to 480 nm) H. Werheit and K.A. Schwetz Solid-state sintering: making a substance from powder by heating it to just below its melting point Liquid-phase sintering: uses an additive that will melt before matrix phase Capillary action pulls liquid into pores, grains rearrange into a better packing arrangement Atoms preferentially go into solution and precipitate in areas of lower chemical potential – called “contact flattening” S-SiC (solid-state sintered) and LPS-SiC (liquid-phase sintered) ordinarily only seen in black only New LPS process can create green LPS-SiC Uses α-SiC powder S-SiC: doped with 0.2% B LPS-SiC: doped with 1.2% Al, 0.3% N, 0.1% O Mixed SiC(Al,N,O) crystal shell, pure SiC core Green is obtained from removal of free carbon G. Pensl and W.J. Choyke, “Optical and Electrical Characteristics of SiC”. Physica B, 185, 264-283 (1993). H. Werheit and K. A. Schwetz, “Comparative optical investigations of sintered and monocrystalline black and green silicon carbide (SiC)”. Journal of Solid State Chemistry, 177, 580-585 (2004).