Structural and optical characterization of CuInSe2 films deposited by hot wall vacuum evaporation method

Copper indium diselenide (CuInSe2) compound was prepared by direct reaction of high-purity elemental copper, indium and selenium. CuInSe2 thin films were deposited onto well-cleaned glass substrates by a hot wall deposition technique using quartz tubes of different lengths (0.05, 0.07, 0.09, 0.11 and 0.13 m). X-ray diffraction studies revealed that all the deposited films are polycrystalline in nature and exhibit chalcopyrite structure. The crystallites were found to have a preferred orientation along the (1 1 2) direction. Micro-structural parameters of the films such as grain size, dislocation density, tetragonal distortion and strain have been determined. The grain sizes in the films were in the range of 65-250 nm. As the tube length increases up to 0.11 m the grain size in the deposited films increases, but the strain decreases. The film deposited using the 0.13 m long tube has smaller grain size and more strain. CuInSe2 thin films coated using a tube length of 0.11 m were found to be highly crystalline when compared to the films coated using other tube lengths; it has also been found that films possess the same composition (Cu/In = 1.015) as that of the bulk. Scanning electron microscope analysis indicates that the films are polycrystalline in nature. Structural parameters of CuInSe2 thin films deposited under higher substrate temperatures were also studied and the results are discussed. The optical absorption coefficient of CuInSe2 thin films has been estimated as 104 cm(-1) (around 1050 nm). The direct band gap of CuInSe2 thin films was also determined to be between 1.018 and 0.998 eV. (c) 2006 Elsevier Ltd. All rights reserved.