A diffusive capture reaction of dopant atoms by relevant host atoms, via the Rideal-Eley mechanism, in GaAs grown by organometallic vapor-phase epitaxy is shown to result in the dopant concentration in the crystal acquiring a dependence on p(Ga) (which is proportional to the growth rate) in agreement with data on S-As, Zn-Ga, and Si-Ga where p(Ga) is the partial pressure of trimethylgallium in the input gas stream. (c) 2007 Elsevier B.V. All rights reserved.