We have investigated the growth of undoped and doped GaN and AlGaN films on both on-axis and 3.5 degrees off-axis 6H-SiC substrates. Scanning electron microscopy showed that the films were smooth and crack free. The typical x-ray rocking curve half-width of the GaN (0002) peak using Cu K alpha x rays was found to be between 9 and 15 arcmin for a 1 mu m film. The crystalline quality improved with increasing thickness. The best films were obtained at the highest growth temperature (800 degrees C) with a 40-50 nm AlN buffer layer grown at the same temperature. The n-type doping up to 4.0 x 10(20) cm(3) was accomplished with silicon, with a 40%-50% activation rate. A calibration curve correlating the n-type carrier concentration in the film with the Si effusion cell temperature was established. The undoped AlxGa1-xN film (x approximate to 0.1) was found to be n type, with a carrier concentration of 7.0x10(18)/cm(3).