An in situ molecular-level study of material growth using a binary reaction sequence of hydride and metalorganic precursors is presented. The study used a model material system of CdS/ZnSe(100) and focused on the material chemistry of heteroepitaxy growth. In the growth process, dimethylcadmium and H2S precursors were sequentially dosed onto a c(2 x 2) ZnSe(100) substrate under high-vacuum conditions. At temperatures of similar to 300 K, saturated chemisorption of a Cd and a S monolayer occurred during each cycle of the binary reaction sequence. Characterization of the growth surface was accomplished in the growth chamber using Auger electron spectroscopy, x-ray photoelectron spectroscopy and low-energy ion scattering spectroscopy fbr probing surface chemical composition and low-energy electron diffraction for determining surface order. These measurements showed layer-by-layer growth at a substrate temperature of similar to 300 K, yielding on ordered stoichiometric CdS film. Strong variations in the composition of the grown surface layer were observed at different substrate temperatures: these variations were found to be related to the temperature dependence of the precursor reactions with the growth surfaces.