Defect chalcopyrite thin films ofCu(In,Ga)2Se3.5were prepared by rf sputtering from stoichiometricCuInxGa1−xSe2(x=0.6)and Na mixture target. The composition of the thin films fabricated in the ratio of[Na]/[Cu(In,Ga)Se2]above 5&percent; was changed from the stoichiometric composition ofCu(In,Ga)Se2to Cu-poor one, and identified asCu:(In+Ga):Se=1:2:3.5.From the results of x-ray diffraction, the lattice parameters of these thin films were slightly smaller than that ofCu(In,Ga)Se2and, besides the peaks appearing for chalcopyrite structureCu(In,Ga)Se2,the additional peak was observed. The optical band gap is increased from 1.24 to 1.36 eV with increasing the[Na]/[Cu(In,Ga)Se2]ratio from 0&percent; to 10&percent; in the target. These films showedn- orp-type conduction. ©1997 American Institute of Physics.