The conduction bands in 6H and 15R silicon carbide I. Hall effect and infrared Faraday rotation measurements

Measurements of infrared Faraday rotation and Hall Effect have been made in a number of specimens belonging to the 6H and 15H polytypes of silicon carbide. Within experimental error the Hall coefficient in these samples was found to be isotropic and it is concluded that the conduction band extrema in both polytypes are most probably located on the symmetry axis. For this model the Faraday rotation results give the effective mass appropriate to directions perpendicular to the axis of symmetry as 0.25±0.02m0 in the 6H polytype and 0.28 ± 0.02m0 in the 15R polytype. Considerable care was required to ensure that the specimens used were uniform in carrier concentration and free from serious crystallographic faults; the precautions taken to meet these requirements and in particular the avoidance of one frequently occurring crystallographic imperfection are described in some detail. All the measurements were made at room temperature.