High-quality 4H-SiC epi layers were grown on 8degrees off-axis (0001) 4H-SiC substrates by chemical vapor deposition (CVD) using a single precursor, bis(trimethylsilylmethane) at a substrate temperature of 1380degreesC. The background doping level of the undoped epi layers was reduced by adjusting of the CVD chamber pressure and Si/C ratio. As the chamber pressure decreased from 360 to 180 Torr, the carrier concentration of the undoped epi layers decreased from 6.8 x 10(16) to 2.0 x 10(16) cm(-3). Moreover, CH4 addition of 10 standard cubic centimeters per minute in the chamber at 180 Torr resulted in the reduction of the carrier concentration to 2 x 10(15) cm(-3), which can be explained by the well-known site-competition effect. The impurity incorporation effect on macrostep bunching was also discussed based on the strong correlation of atomic force microscopy topologies and impurity concentration. As the flow rate of nitrogen gas (N-2) increased, the electron concentration of the epi layers linearly increased. With variation of the N-2 flow rate, a total n-doping range from 2.0 x 10(17) to 1.0 x 10(21) cm(-3) was achieved. (C) 2004 The Electrochemical Society.