Far-infrared absorption and DC conductivity measurements in SiC

4H–SiC and 6H–SiC single crystals have been studied by far-infrared(FIR) absorption and DC measurements. In FIR absorption measurements a peak 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 dependence of the absorption intensities for 6H–SiC peaks strongly depends on the concentration of doped nitrogen donor. It was interpreted as an effect due to the change in plasma frequency in connection with doped nitrogen. From DC conductivity measurements for 6H–SiC, it is deduced that the hopping energy ε3 is 13 meV.