An impurity source film is formed along a portion of a non-planar semiconductor fin structure. The impurity source film may serve as source of an impurity that becomes electrically active subsequent to diffusing from the source film into the semiconductor fin. In one embodiment, an impurity source film is disposed adjacent to a sidewall surface of a portion of a sub-fin region disposed between an active region of the fin and the substrate and is more proximate to the substrate than to the active area.