Epitaxial layers and superlattices of GaAsN/GaAs were grown by metalorganic molecular beam epitaxy using dimethylhydrazine, triethylgallium, and conventional arsenic sources. The incorporation of nitrogen into the solid was investigated as a function of the substrate temperature and the flux of dimethylhydrazine and modeled assuming formation of an adduct. Growth of GaAsN is characterized by an activation energy of 0.97 eV arising from a difference between activation energies of the adduct sticking coefficient, EB∼1.27eV, and the adduct formation, EA∼0.3eV. Nitrogen incorporation of 3% is obtained at a growth temperature of 400°C. High-resolution x-ray diffraction and photoluminescence data demonstrate excellent quality of epitaxial layers and superlattices grown with dimethylhydrazine.