FAR-INFRARED ABSORPTION AND DC CONDUCTIVITY MEASUREMENTS IN SIC

4H-SiC and 6H-SiC single crystals have been studied by far-infrared(FI R) absorption and DC measurements. In FIR absorption measurements a pe ak at 266 cm(-1) for 4H-SiC and two peaks at 235 cm(-1) and 240 cm(-1) for 6H-SiC were observed. It was found that the temperature dependenc e of the absorption intensities for 6H-SiC peaks strongly depends on t he concentration of doped nitrogen donor. It was interpreted as an eff ect due to the change in plasma frequency in connection with doped nit rogen. From DC conductivity measurements for 6H-SiC, it is deduced tha t the hopping energy epsilon(3) is 13 meV. (C) 1998 Published by Elsev ier Science S.A. All rights reserved.