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  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 4H- SiC (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 SiO 2

(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 P 0, R 0, S 0 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, A 0  4A – acceptor four-particle neutral complex  A 0 associated with Ti in 6H-SiC

Comparison of photoluminescence spectra ( 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, A 0, B 0, C 0, 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, (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, (2004).