Electrical transport in n-type 4H silicon carbide

Free electron density and low field electron mobility of 4H–SiC in the temperature range of 35–900 K are examined experimentally and theoretically. Five samples produced by cold-wall atmospheric pressure chemical vapor deposition and doped with nitrogen from 3.5×1015 cm−3 to 7.5×1017 cm−3 are investigated using the electric conductivity and Hall measurements. A complete description of the electron density and mobility is presented taking into account inequivalent positions of cubic and hexagonal donor sites as well as valley-orbit splittings of the donor levels. A good agreement between experiment and theory is achieved for all samples and it is demonstrated that the scattering of electrons by neutral donors is a dominant mode in 4H–SiC at low temperatures. The deformation potential for the intravalley scattering by acoustic phonons and coupling constants for the intervalley scattering by acoustic and optic phonons are determined. The dependence of electron mobility on doping at constant temperatures 77 K, 292 K, and 600 K is experimentally established and successfully described. Parallel conductivity at low temperatures by an impurity band in the sample with 7.5×1017 cm−3 donors is evidenced.