Investigation of copper indium gallium selenide material growth by selenization of metallic precursors

We report a study of copper indium gallium selenide (CIGS) thin film growth in the annealing process at temperature range from 120 C to 600 C. Thin films were prepared by sputtering metal precursors and subsequent selenization process. Surface morphologies of thin films were observed by using high resolution field emission scanning electron microscopy (FESEM). Phases in quaternary systems Cu-In-Ga-Se were investigated by X-ray diffraction (XRD). Evolution of crystalline structure in the film surface was studied by Raman spectra. A possible reaction path from metallic precursors to a single CIGS phase was obtained by merging all results of SEM, XRD and Raman. Above 210 C, selenium reacted with Cu and In to form binary selenide. CuSe crystalline platelets were observed clearly in the film surfaces. When temperature was reaching 380 C, Cu_2-xSe and InSe reacted with excess Se to form CuInSe₂ (CIS) and contributed to the grain growth. Above 410 C, Ga-rich phase was detected in the films. With increased temperature, Ga diffused into CIS crystalline lattices. Finally, at 600 C, a single phase of Cu-In-Ga-Se quaternary system was formed. A large number of triangular and hexagonal structures were observed in the film due to a re-crystalline process at a high annealing temperature.