BAND-STRUCTURE ANALYSIS OF THE CONDUCTION-BAND MASS ANISOTROPY IN 6H AND 4H SIC

The band structures of 6H SiC and 4H SiC calculated by means of the full-potential linear-muffin-tin-orbital method are used to determine the effective mass tensors for their conduction-band minima. The results are shown to be consistent with recent optically detected cyclotron resonance measurements, which find the ratio of cyclotron masses for B perpendicular to c to B parallel to c to be larger (smaller) than unity for the 6H (4H) polytype. However, contrary to previous suggestions, appreciable anisotropies in the c plane are found. For 6H SiC, a strong dependency on band filling is predicted because of the occurrence of a double-well minimum along the ML axis. The calculated mass tensors for 3C and 2H are also reported.