Using the inelastic background in hard x-ray photoelectron spectroscopy for a depth-resolved analysis of the CdS/Cu(In,Ga)Se2 interface.

The inelastic background of hard x-ray photoelectron spectroscopy data is analyzed to paint a depth-resolved picture of the CdS/Cu(In,Ga)Se₂ (CdS/CIGSe) layer structure. The CdS/CIGSe interface is the central component in next-generation chalcopyrite thin-film photovoltaic devices. By analyzing both, the (unscattered) core-level peaks and the inelastic background, and by varying the excitation photon energy from 2.1 up to 14 keV, we can derive photoemission information over a broad range of electron kinetic energies and, hence, sampling depths. With this complementary information, the CdS film thickness of a CdS/CIGSe interface can be accurately determined as a function of the CdS deposition time. For the thinner CdS films, the film thickness can be shown to vary laterally. Furthermore, small amounts of Se and process-related Rb can be detected in a thin (∼2 nm) surface layer of all investigated CdS films. [ABSTRACT FROM AUTHOR]