The segregation behavior of carbon during the GaAs LEC process is described by a combined carbon and oxygen transport model. For this attempt the well-known Scheil formalism was extended by consideration of the incorporation and extraction of carbon via CO transport through the encapsulating boron oxide. The influence of the changing oxygen potential was included in order to describe the experimental data, especially for low carbon levels. The model is helpful for the adjustment of growth parameters relevant for carbon doping in order to achieve a homogeneous carbon distribution at any specified level, (C) 2002 Elsevier Science B.V. All rights reserved.