High-speed homoepitaxy by horizontal cold-wall chemical vapor deposition (CVD) was investigated. Improvement of initial growth condition lead to good surface morphology even with high SiH4 flow rates. However, the growth rate was found to be saturated at 6 mum/h, the cause of which is speculated to SiH4 polymerization. The dependencies of doping characteristics and the Z(1) center concentration on SiH4 flow rates were investigated, which suggested that the effective C/Si ratio increases with increasing SiH4 flow rate. These results support the above speculation, because the SiH4 polymerization decreases the relative amount of Si species contributing to SiC growth in the reaction system, resulting in the effectively high C/Si ratio.