ABSTRACT
Chemical reaction between Cu(In,Ga)Se2 (CIGS) and Mo layers as well as the crystal growth of CuInSe2 (CIS) in physical vapor deposition (PVD) were studied by x-ray diffraction and both high resolution and analytical transmission electron microscopy (TEM). MoSe2 was observed at the CIGS/Mo interface in device quality CIGS film deposited using the “3-stage” process. The characterization of various Cu-In-Ga-Se films deposited on Mo layer showed that the MoSe2 layers formed under (In,Ga)-rich CIGS growth conditions as early as the 2nd stage of the 3-stage growth process. A growth model for CIS crystals under Cu and Se excess conditions is proposed based on the results of the TEM observations of Cu-rich CIS film. The characteristics of the CIS growth model in PVD can be summarized as follows (1) sphalerite and/or CuPt type (Cu,In)Se crystals are produced first from C¾Se crystals by a “topotactic reaction”, (2) the metastable sphalerite and/or CuPt type (Cu,In)Se then transforms to the stable chalcopyrite CIS.phase.
