A remote plasma enhanced CVD apparatus and method for growing semiconductor layers on a substrate, wherein an intermediate feed gas, which does not itself contain constituent elements to be deposited, is first activated in an activation region to produce plural reactive species of the feed gas. These reactive species are then spatially filtered to remove selected of the reactive species, leaving only other, typically metastable, species which are then mixed with a carrier gas including constituent elements to be deposited on the substrate. During this mixing, the selected spatially filtered reactive species of the feed gas chemically interacts, i.e., partially dissociates and activates, in the gas phase, the carrier gas, with the process variables being selected so that there is no back-diffusion of gases or reactive species into the feed gas activation region. The dissociated and activated carrier gas along with the surviving reactive species of the feed gas then flows to the substrate. At the substrate, the surviving reactive species of the feed gas further dissociate the carrier gas and order the activated carrier gas species on the substrate whereby the desired epitaxial semiconductor layer is grown on the substrate.