Synthesis and Optical Properties of CuInSe₂ Films

Abstract

The growth of CuInSe₂ films via evaporation from a compound source is studied by x-ray diffraction and x-ray fluorescence analysis. It is shown that, on heating, CuInSe₂ dissociates into copper and indium selenides, which partially vaporize before film deposition. At the beginning of the deposition process, the source consists mainly of Cu₂Se, CuInSe₂ , and In₂Se₃ in different ratios, depending on the source temperature. During deposition, two phases vaporize for the most part: CuInSe₂ and In₂Se₃ or Cu₂Se and CuInSe₂ , depending on the source temperature. As a result, some of the selenium, a highly volatile component, is lost, and the grown films consist of Cu₂Se _x (x ≤ 1), Se-deficient CuInSe₂ , and InSe. At a source temperature of 1040°C, the impurity phases vaporize at approximately equal rates, and the grown films consist of CuInSe₂ only. During continuous heating of the source, all the decomposition products are transferred to the substrate, and the film is very close in composition to the source. The chemical composition and structure of the films are determined, and their optical absorption spectra are measured near the fundamental edge at 290 K. The absorption data are used to evaluate the band-structure parameters of CuInSe₂ . A technique is proposed for assessing the band structure of this compound.