Polycrystalline Cu(In1−xGax)3Se5thin films were prepared by four source evaporation with controlling and shielding of the molecular beams from elemental sources. Ga contentx, can be controlled by deposition times of CuIn3Se5and CuGa3Se5layers, which form Cu(In1−xGax)3Se5films through the interdiffusion. X‐ray diffraction analyses showed that the films withx≲0.5 have an ordered vacancy chalcopyrite and the films withx≳0.5 have a zinc blende structure. The optical band gap of the films linearly increased from 1.23 eV (x=0) to 1.85 eV (x=1) with increasing Ga content. The conductivity of the films was about 10−6/&OHgr; cm and about 10−7/&OHgr; cm under and abovex=0.3, respectively. ©1995 American Institute of Physics.