Preliminary results are presented on the growth and characterization of Cu-In-Se-S thin films formed by reaction of Cu-In layers with aH2Se/H2Sgas mixture. The approach was to first develop a process to grow device qualityCuInS2films by reaction of a Cu-In layer inH2S.This process was then modified to form alloyedCuIn(Se,&hthinsp;S)2films. A quantitative model for the reaction of Cu-In films in a CVD reactor with a mixedH2S-H2Seflowing gas was developed and verified. The composition of theCuIn(Se,&hthinsp;S)2film can be controlled by the concentrationH2Se+H2Sand/orSe2+S2in the gas phase. Graded films can be made by annealing eitherCuInSe2orCuInS2films in a controlled Se and/or S containing atmosphere. Expanding this to include Ga in the films will provide a basis for engineering film compositions and bandgaps. ©1999 American Institute of Physics.