Extended soft X-ray emission spectroscopy: quantitative assessment of emission intensities

Abstract

Soft X-ray emission spectroscopy (SXES) in the energy range between 150 eV and 1500 eV has typical attenuation lengths between tens and a few hundred nanometres. In this work the transmission of soft X-rays in synchrotron-based SXES has been quantitatively analysed using specially prepared layer samples. The possibility of extending the standard qualitative analysis of SXES by exploiting the information underlying the emission intensity was examined for thin layer structures. Three different experiment series were accomplished with model layer systems based on different sulfur-containing substrates: (i) MoS(2), (ii) CuInS(2), (iii) Cu(In,Ga)(S,Se)(2). The absorption of the S L(2,3) emission line by ZnO cover layers of up to 80 nm thickness was monitored and compared with theoretical expectations. By comparison with a reference intensity recorded from a bare substrate, the attenuation of the S L(2,3) emission could be used to accurately determine the ZnO overlayer thickness up to a critical thickness, depending on the set-up and the net S L(2,3) emission intensity. The results from these local energy-resolved spot measurements were compared with spatially resolved scans of the integral S L(2,3) emission intensity over areas of several mm(2). In the scan images the attenuation of the S L(2,3) emission intensity clearly reflects the local ZnO layer thickness. From the attenuation the ZnO layer thicknesses were calculated and compared with ellipsometric measurements and were found to be in excellent agreement. These results demonstrate the benefits of a quantitative analysis of SXES, making it an even more powerful tool for examining buried interfaces and for monitoring lateral inhomogeneities.

Synchrotron-based spectroscopy for the characterization of surfaces and interfaces in chalcopyrite thin-film solar cells

“…A non-destructive analysis method with an information depth (ID) in the depth regime similar to that of the space charge region in CIGSSe devices (some few hundred nanometer) is highly desirable. The combination of surface sensitive PES and near-surface bulk sensitive XES measurements provides information related to elemental composition, chemical bonding and valence electronic states of a specimen on the desired depth scale [10][11][12][13]. In the following two sub-sections the application of XPS and XES for the analysis of the surface and near-surface bulk of chalcopyrite absorbers and layer systems thereof is shown.…”