NOVELTY - Process for characterizing a composition of an alloy layer of I-(II, III)-(VI-V) type, comprises generating resonance Raman phenomenon, during the illumination of the alloy layer by incident radiation of wavelength close to a wavelength of the width of alloy band gap; measuring the intensity of a Raman diffusion peak characteristic of the alloy of the layer; and determining, according to the measure of the intensity, 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.    USE - The process is useful for characterizing a composition of an alloy layers, where the composition is useful in the design of solar panels in which thin layers of the alloys are involve as active part of the photovoltaic cell.    ADVANTAGE - The composition has good photovoltaic property.    DETAILED DESCRIPTION - Process for characterizing a composition of an alloy layer of type I-(II, III)-(VI-V), where: I is an atomic species in the first column of the periodic table; II is a first atomic species of the third column of the periodic table; III is a second atomic species in the third column of the periodic table; VI is a first atomic species in the sixth column of the periodic table; V is a second atomic species in the sixth column of the periodic table, and the process comprises, generating resonance Raman phenomenon, during the illumination of the alloy layer by incident radiation of wavelength close to a wavelength of the width of alloy band gap: measuring the intensity of a Raman diffusion peak characteristic of the alloy of the layer; and determining, according to the measure of the intensity, 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. INDEPENDENT CLAIMS are included for:    (1) a device for carrying out the process comprising a laser source (10), Raman probe (11), and calculation means (12) for measuring the intensity of a Raman diffusion peak characteristic of the alloy layer, and determining, according to the measure of intensity, 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; and    (2) a computer program comprising instructions for implementing, when this program is executed by a processor, the steps of the process.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of the device for the carrying out the process.    Laser source (10)    Raman probe (11)    Calculation means for measuring the intensity of a Raman diffusion peak characteristic of the alloy layer (12)    Laser exit (LAS)    First optical fiber. (FOI)