Raman spectroscopy for quality control and process optimization of chalcopyrite thin films and devices

We will demonstrate in this paper that Raman scattering of visible light is a versatile tool both for research and industrial process monitoring of thin chalcopyrite films for solar cells. Thin films of Cu(In, Ga)(S,Se)2 (CIGSSe) are produced by rapid thermal processing of stacked elemental Cu–In–Ga–Se layers. The Raman investigations are accompanied by grazing incidence X-ray diffraction (GI–XRD) and X-ray florescence (XRF) measurements. GI–XRD measurements confirm that the films show a two-fold elemental gradient: a sulfur gradient from the top and a Ga gradient from the CIGSSe/Mo interface. By Rietveld refinement of the GI–XRD spectra of the surface–near (∼ 100nm) ratio of sulfur to selenium can be obtained which corresponds well to the intensity ratio of the two Raman A1 modes of CuInS2 and CuInSe2. The asymmetric line shape of both XRD diffractograms and Raman spectra is attributed to the sulfur gradient. In addition we show that the intensity ratio of the satellite Raman B and E modes shows a correlation with the Cu to In + Ga ratio obtained by XRF.