A method for forming a deposited film comprises forming a gaseous atmosphere of a silane compound represented by the general formula: Si.sub.n H.sub.2n+2 (n.gtoreq.1) and a halogen compound in a deposition chamber in which a substrate is arranged, and exciting and decomposing these compounds by utilization of photoenergy thereby to form the deposited film containing silicon atoms on said substrate.A method for forming a deposited film comprises forming a gaseous atmosphere of a silane compound represented by the general formula: Si.sub.n H.sub.2n+2 (n.gtoreq.1), a halogen compound and a compound containing atoms belonging too the group III or the group V of the periodic table in a deposition chamber in which a substrate is arranged, and exciting and decomposing these compounds by utilization of photoenergy thereby to form a deposited film containing silicon atoms and the atoms belonging to the group III or the group V of the periodic table on said substrate.