Rapid thermal chemical vapor deposition (RTCVD) of in-situ doped N and P-type thin single crystal silicon layers has been accomplished in a cold wall environment. Dichlorosilane, SiH2C12, is used for the silicon source, B2H6 and AsH3 for the dopant sources. Special attention is paid to minimize the oxygen and carbon contamination of the silicon surface prior to the deposition. As a result of process optimization, the total thermal budget of the RTCVD is reduced, junction abruptness is enhanced, dopant movement is minimized and the process-induced defects in the grown layer are remarkably reduced. The layers of single crystal silicon are examined by Fourier-transform infrared spectroscopy (FTIR), for thickness measurement and uniformity, modified Schimmel etch and Nomarski interference microscopy for defect delineation , secondary ion mass spectrometry (SIMS) and spreading resistance profile (SRP) for dopant profiling and junction depth measurements. Under optimized process conditions, single crystal silicon layers of high degree of structure quality with transition widths of 0.1 to 0.16 micron for three orders of magnitude change in dopant concentration are deposited. A systematic approach to optimize the process conditions for deposition of high quality and well-controlled single crystal silicon films is presented. It is demonstrated that the pre-growth process step(s) has a profound effect on the crystal quality of the grown layers. The process control features of RTCVD technology are addressed and the applications of thin, controllably-doped single crystal silicon layers for MOS and bipolar technologies are discussed.