Characterization of group I-rich growth during (Ag,Cu)(In,Ga)Se2 three-stage co-evaporation

(Ag,Cu)(In,Ga)Se₂ thin-films with bandgap 1.3 - 1.6 eV were deposited by three-stage elemental co-evaporation and the group I-rich growth in the second stage of the process was characterized. By interrupting the three-stage growth at the end of the second stage, films were obtained with surface layers of Ag-Cu-Se compounds and underlying chalcopyrite (Ag,Cu)(In,Ga)Se₂ layers. Composition measurements and depth profiles showed higher Ag/(Ag+Cu) ratio in the Ag-Cu-Se layers than in the underlying chalcopyrite. Plan-view images from scanning electron microscope suggested that Ag-Cu-Se was present in a liquid phase at reaction temperature during the second stage and that its morphology was different than the corresponding Cu₂Se and Cu_2-xSe phases from a Cu(In,Ga)Se₂ deposition. Glancing incidence x-ray diffraction measurements identified Cu₂Se, CuAgSe, Cu_0.5Ag_1.5Se and Ag₂Se possible phases.