Real-time studies of phase transformations in Cu–In–Se–S thin films 2. Sulfurization of Cu–In precursors

Phase transformations during sulfurization of thin films of elemental Cu, elemental In, and intermetallic Cux  In with x=(1.7,1.0,0.8)x=(1.7,1.0,0.8) are investigated using real-time energy dispersive X-ray diffraction. From the temporal development of the X-ray peak intensities, phase predominance sequence diagrams are constructed including the intensity ratio of the CuKα/InKα fluorescence lines. Sulfurization of elemental Cu layers starts at room temperature. CuS is found as an intermediate phase and as the final phase being stable below about 260 °C. Sulfurization of elemental In passes the phase In5S4 and leads to the final phase α-In2S3. During sulfurization of CuxIn films, intermetallic phase transformations take place in parallel to the sulfurization reactions. CuInS2 in general grows by the consumption of Cu–In intermetallic phases. Its growth is most rapid in the heating period of the process. This is interpreted as a stress-induced growth phenomena. Coverage of a final Cu-rich CuInS2 film with Cu2−xS during the high temperature period is revealed. Thermal expansion coefficients for several intermetallic and sulfidic phases are derived from the temperature dependence of the lattice constants.