Diethyl aluminum chloride and diethyl gallium chloride were successfully employed as precursors for the epitaxial growth of AlxGa1-xAs. The composition, thickness, and compositional uniformity of these layers were strong functions of the growth temperature, as determined with double-crystal x-ray diffraction and photoluminescence measurements. A thermodynamic model based on the free energy minimization of the expected gas and solid phase constituents is presented to explain these trends and other growth chemistry effects. Selective epitaxy was also investigated. AlxGa1-xAs was selectively grown on GaAs wafers masked with Si02 or Si3N4 under certain conditions. In contrast, AlAs growth was not selective. Selectivity of AlxGa1-xAs improved with increasing diethyl gallium chloride mole fraction and with increasing temperature, in accordance with thermodynamic considerations. Thermodynamic analysis of this growth chemistry indicates that various multinary semiconductors can be grown selectively using related metalorganic-chloride precursors. © 1991, The Electrochemical Society, Inc. All rights reserved.