We used the process simulator FLOOPS-ISE to implement a consistent model describing the diffusion behaviors of boron and carbon in silicon and silicon germanium. In particular, our model successfully accounts for boron and carbon behaviors in a wide range of sample structures and experimental conditions over the complete temperature range of 750-1070 degrees C in inert and oxidizing ambients, and in the presence of implant damage. The structures studied include cases where the boron and carbon profiles are separated as well as cases where profiles overlap, cases with carbon in silicon and in SiGe, and our own recent experiments where boron diffusion within a SiGeC region has been characterized. We model carbon diffusion by the kickout and Frank-Turnbull mechanisms, and interstitial capture by substitutional carbon, and demonstrate that a model must incorporate all three effects to satisfactorily explain published data. We also include standard models for boron-interstitial clusters and {311} defects. (c) 2006 American Vacuum Society.