Nucleation and growth of the CdS buffer layer on Cu(In,Ga)Se2 thin films

In this work, the nucleation and growth of the CdS buffer layer (chemical bath deposition) on Cu(In,Ga)Se₂. (CIGS) thin films was observed using the surface-specific methods of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). The AFM images show islands at short deposition times (<30 s) whereas XPS measurements do not register any sulfur on these surfaces. The authors postulate that Cd(OH)₂ precipitates out of the basic deposition solution while rinsing it off the CIGS surface, thus creating the islands. All methods used here indicate the onset of bulk CdS growth after about 30 s deposition time. According to the AFM images, the entire CIGS surface seems to be covered within 1 min deposition. This is confirmed by SE, which shows bulk layer growth after 1 min; it increases at about 0.4 nm/s after the induction phase