Optical and electrical properties of CuIn1-xGaSe2 thin films obtained by selenization of sequentially evaporated metallic layers

The aim of this work was to study the dependence of the optical, electrical and structural properties of CuIn1-xGaSe2 (CIGS) thin films on different parameters such as Cu/(In + Ga) and Ga/(In + Ga) ratios and film thicknesses. CIGS thin films have been deposited in a two-stage process. In the first stage, the metallic precursors were evaporated on glass substrates following the In/Ga/Cu/In sequence. The selenization, named the second stage, was performed inside a partially cloned graphite box. This process was realized at 500 degreesC in vacuum with elemental selenium vapour. The obtained polycrystalline CIGS films showed the chalcopyrite structure with predominant growth in the (1 12) direction. The band gap energy was E-g = 0.93-1.58 eV, being higher for higher Ga/ (In + Ga) and near stoichiometric Cu/ (In + Ga) atomic ratios. The electrical conductivity sigma measured in the 40-370 K range, was found to increase with Cu content and to present a conductivity activation energy of 0.034 eV between 240 and 370 K. (C) 2003 Elsevier Science B.V. All rights reserved.