Investigation of chalcopyrite film growth: an evolution of thin film morphology and structure during selenization

In this work, we report a study of the evolution of Cu–In–Ga–Se system during selenization. The metallic precursors were selenized in Se vapour atmosphere at temperature range from 210 to 380 °C. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectra were used to investigate morphological and structural properties of the films. A great amount of thin platelets appeared in the film surfaces at temperature range from 210 to 270 °C. Most platelets had hexagon or polygon structures. The average sizes of these platelets increased with the temperatures. TEM analyses indicated that these platelets had γ-CuSe phases. Beyond 310 °C, most of CuSe platelets decomposed under release of selenium and formed Cu_2−xSe. Cu_2−xSe might react with InSe for the formation of tetragonal CuInSe₂. The average grain sizes increased obviously with the increased temperatures. A possible reaction path to obtain a chalcopyrite structural film was discussed in the end. In addition, Ga was detected rich in the bottom of the film by energy dispersive spectroscopy and grazing incidence X-ray diffraction.