Existing data describing the dependence of the concentrations of the defects S-As, Zn-Ga, Si-Ga, Sb-Ga, and EL2 in GaAs grown by organometallic vapor phase epitaxy on the partial pressures of arsine (P-As) and the dopant-containing gases in the input gas stream are analyzed using a simple model. It is found that (1) AS(4) is the dominant species of As in the vapor in equilibrium with the solid at the growth interface, (2) the electron concentration governing the charge state of the defect being formed is proportional to P-As(3/4) independent of the dopant concentration, (3) the Fermi level during the defect formation process lies above the ionization levels of deep donors but below that of shallow donors, and (4) the atomic structure of the mid-gap electron trap, EL2, is stoichiometrically equivalent to the arsenic antisite, As-Ga. (C) 2002 Elsevier Science B.V. All rights reserved.