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

Abstract

Growth of Cu(In,Ga)Se2 (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)2Se3 → [Cu(In,Ga)5Se8] → Cu(In,Ga)3Se5 → Cu(In,Ga)Se2. The grain size increased from the sub-micron grains of the (In,Ga)2Se3 precursor film to several micrometers in the stoichiometric Cu(In,Ga)Se2 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.

In situ diagnostic methods for thin‐film fabrication: utilization of heat radiation and light scattering

“…In the case of Cu(In,Ga)Se 2 (CIGS) chalcopyrite absorbers, key parameters, including the deposition temperature, thickness and deposition speed 1,2 have been intensively investigated. Also, Se pressure [3][4][5] , the compositional ratios of Cu/(In þ Ga) (¼ Cu/III) 6 and Ga/(In þ Ga) (¼ Ga/III) [7][8][9] play critical roles in the properties of CIGS films and fabricated cells. In 1994, a three-stage process was developed, which deposits (In,Ga,Se) and (Cu,Se) alternatively, drastically varying the Cu/III ratio.…”