Sintered and Monocrystalline Black and Green Silicon Carbide-Optical Properties

摘要

Crystalline SiC obtained by the Acheson-Process occurs in different polytypes, which are colorless transparent or variously colored due to doping with different elements. Dense sintered SSiC (solid-state sintered) and LPSSiC (liquid-phase sintered) were known in black color only, but recently green LPSSiC was achieved by a new liquid phase sintering process. To characterize the chemical compositions of these SiC materials high-resolution Auger electron spec-troscopy (HRAES) additionally to bulk chemical analyses have been performed. In LPSSiC, the grain boundaries exhibit extremely thin (～1 nm) segregation films with compositions formally corresponding to x SiO{sub}2 · y AlN. The black colour of polycrystalline sintered SiC bodies (S and LPS variants) appears to result from small amounts of elemental carbon (≥ 0,2 mass-% C). Sintering after removing the free carbon by a suitable oxidation process leads to green LPS-SiC.