Iron nitride films were grown by atomic-nitrogen-assisted molecular beam epitaxy. ZnS-type FeN (gamma ''-FeN) was synthesized with low Fe evaporation rates (<= 0.2 angstrom/s) at low growth temperatures below 210 degrees C whereas gamma'-Fe4N was synthesized with high Fe evaporation rates (>= 1.0 angstrom/s) at 130-415 degrees C. Our results indicate that the stabilization of ZnS-type FeN requires not only the fulfillment of thermodynamic constraints but also the control of a delicate balance of kinetically driven competition. The use of lattice-matched GaN(0001) substrates enables the growth of epitaxial films of ZnS-type FeN. (C) 2015 Elsevier BY. All rights reserved.