We investigated the effect of the incorporation of O atoms into BaSi2 films on their photoresponse properties. BaSi2 films with higher O concentration exhibited higher photoresponsivity. Time-of-flight secondary ion mass spectrometry measurements showed that the O atoms were uniformly distributed in the BaSi2 films, in contrast to our prediction that they would be mostly located around grain boundaries. First-principles calculations revealed that the O atoms occupy the interstitial sites known as the 4c sites rather than substitutional sites. Moreover, they do not create localized stateswithin the forbidden band gap, which indicates that O atoms incorporated into BaSi2 are inactive. (C) 2017 Elsevier B.V. All rights reserved.