The incorporation of silicon in GaAs layers grown by metal-organic chemical vapor deposition has been studied using two different doping sources, silane and disilane. Epitaxial layers were grown on <100>, <111>A, and <111>B surfaces over a wide range of growth temperature and gas phase stoichiometry. When using silane, an influence of the substrate orientation on silicon incorporation was found. This behavior can be described by a qualitative model involving both the surface specific adsorption sites and possible surface chemical reactions. In the case of disilane, the incorporation process appears to be independent of substrate orientation and growth temperature. This temperature independence results in improved uniformity of the electron concentration over large substrate areas when disilane is used as the doping gas. © 1985, The Electrochemical Society, Inc. All rights reserved.