The effect of growth temperature and substitutional carbon on phosphorus autodoping in Si grown by low pressure rapid thermal chemical vapor deposition was investigated. In the temperature range between 550 and 700degreesC, phosphorus autodoping decreased with decreasing temperature. The incorporation of substitutional carbon at 550degreesC further suppressed autodoping. Using a combination of 550degreesC growth and substitutional carbon incorporation, we achieved abrupt phosphorus transitions over three decades of phosphorus concentration. These transitions were characterized by a slope of 11+/-1.5 nm/decade. (C) 2003 The Electrochemical Society.