High quality FeSe thin films with different ratios of Fe to Se have been grown on GaAs and Si substrates by changing the flow rate of Fe(CO)5 in a low-pressure metal–organic chemical vapor deposition (MOCVD) system. For both substrates, the films grown at a low flow rate of Fe(CO)5 are non-ferromagnetic and exhibit superconductivity at low temperature, while those grown at a high flow rate of Fe(CO)5 display ferromagnetic and semiconducting behaviors. Our results suggest that the superconducting phase does exist in a narrow range of Fe and Se concentration near stoichiometry. The introduction of excess Fe favors ferromagnetism and leads to the suppression of superconductivity.
