Physics and Chemistry in Physical Vapor Deposition of Cu(In,Ga)Se2 Thin Films

Growth of Cu(In,Ga)Se-2 (CIGS) thin films during the physical vapor deposition (PVD) were characterized by scanning Auger electron spectroscopy (SAES), secondary ion mass spectroscopy (SIMS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The deposition processes are comparable with the 2nd and 3rd stages of the "3-stage" process. The phase changes observed in CIGS films during the 2nd stage of the "3-stage" process were as follows: (In,Ga)(2)Se-3 -> [Cu(In,Ga)(5)Se-8] -> Cu(In,Ga)(3)Se-5 -> Cu(In,Ga)Se-2. The grain size increased from the sub-micron grains of the (In,Ga)(2)Se-3 precursor film to several micrometers in the stoichiometric Cu(In,Ga)Se-2 film. Growth mechanism of CIGS crystal are discussed on the basis of the phase diagram of the Cu2Se-In2Se3 pseudo-binary system, and crystal structures and stacking sequences of Se atomic layers of compounds in the In2Se3-Cu2Se system.