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

Abstract

Phase transformations during sulfurization of thin films of elemental Cu, elemental In, and intermetallic Cu x In with 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 CuK α/InK α 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 In 5S 4 and leads to the final phase α-In 2S 3. During sulfurization of Cu x In films, intermetallic phase transformations take place in parallel to the sulfurization reactions. CuInS 2 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 CuInS 2 film with Cu 2− x S 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.