Anisotropy of Electron Mobility in n-Type 15R-SiC Studied by Raman Scattering

LO-phonon-plasmon coupled modes in n-type 15R-SiC bulk crystals with free carrier concentration of n=1016#~1018 cm-3 were observed by Raman scattering. The axial-type mode for which the plasma oscillation and atomic displacements occur along the c-axis, and the planar-type mode for which these oscillations occur in the c- plane, were separately observed. A spectral line-shape analysis was done using three adjustable parameters for free carrier concentration, plasmon damping rate and phonon damping rate. Carrier mobilities parallel and perpendicular to the c-axis (*m#p and *mBB respectively) were evaluated from the results, showing a weak anisotropy as *m#p/*mBB=1.8 #+ 0.3. This result is in agreement with a previous Hall measurement, and is qualitatively similar to the case of n-type 6H-SiC.