The incorporation of carbon into GaAs grown by metalorganic vapor phase epitaxy has been studied through the addition of the halomethanes CCl4, CHCl3, CH2Cl2, CBr4, CI4, CHI3, CH2I2, CH3I and CH4. Growth temperatures of 600-750°C, V/III ratios of 30-100, and halomethane mole fractions of 2 × 10-8-1 × 10-4 were investigated. The incorporation of carbon for all the halomethanes decreases at high V/III ratios and also decreases at high growth temperatures with an exponential Arrhenius fitting parameter of -30 to -60 kcal/mol. The carbon incorporation dependence of the chloromethanes on halomethane mole fraction conforms to a first order power function. However, carbon incorporation with CH2I2 conforms to a second order power function. The trend in the halomethanes is to incorporate carbon more efficiently in more highly substituted halomethanes, following the series CH3X < CH2X2 < CHX3 < CX4 throughout the range V/III ratios and growth temperatures investigated. good correlation in this series of low average bond strength to carbon incorporation is also observed. The dependence of carbon incorporation on V/III ratio and growth temperature are explained by a simple reaction scheme based on the competition at the growing interface between the decomposition of the halomethane to incorporate carbon and the desorption of the decomposing halomethane from the interface. © 1991.