TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Process: The process comprises, after the step of measurement, comparing with at least a measurement of reference intensity of the same Raman diffusion peak on at least one standard alloy of the same type as the alloy of the layer and of known composition, and, according to the comparison, determining at least one variation with respect to the standard alloy, a proportion of the species II with respect to the species III, and/or species VI with respect to the species V, in the alloy of the thin layer. The process comprises comparison with several reference intensity measurements of the same Raman diffusion peak on several standard alloys of the same type as the alloy of the layer and of different known compositions. The process further comprises measurement of a position in wavelength of maximum intensity of photoluminescence to determine the width of alloy band gap and completing the characterization of the alloy composition. Preferred Components: The alloy is of formula (CuIn(SySe1-y)2), where the wavelength of incident radiation is needed to obtain resonance or Raman pre-resonance involving a high intensity of the measured Raman diffusion peak. In the alloy composition, the wavelength of the incident radiation is 785 nm. The Raman diffusion peak corresponds to a mode of vibration of type E(L)/B2(L) of the alloy. The Raman diffusion peak is located at a frequency of 340-350 cm-1. The alloy is of formula (Cu(InxGa1-x)(Se)2), and (Cu(InxGa1-x)(S)2), where wavelength of incident radiation is needed to obtain a resonance or pre-resonance Raman involving high intensity of the measured Raman diffusion peak. The wavelength of radiation is of the order of: 785 nm for a composition x less than 0.6 and 930 nm for a composition x greater than 0.6. The wavelength of incident radiation is less than a wavelength corresponding to the width of alloy band gap to simultaneously measure the maximum intensity of photoluminescence. The alloy is penternary of type of (Cu(InxGa1-x)(SySe1-y)2). The laser source is of titanium-sapphire tunable of 700-1030 nm.y = 0-1, preferably 0.65-1; andx = 0-1.