Crystal growth of Cu(In,Ga)Se2 film by RTP annealing of the stacked elemental layers formed by E-beam evaporation

• CIG was deposited as a formation of stacked elemental layers by E-beam evaporation.
• The atomic ratios of each element of CIG were optimized by varying of thickness.
• CIGS films were obtained by the selenization of the CIG SEL using RTP process.
• The selenization was carried out in a quartz box to prevent the loss of Se.
• The homogeneous and dense CIGS films were obtained with a grain size of 2 μm.

Cu(In,Ga)Se2 (CIGS) thin films were successfully prepared by the application of a rapid thermal process to the stacked elemental layers (SEL), which were deposited by electron-beam (E-beam) evaporation method in the sequence of Cu/In/Ga/…/Cu/In/Ga. For the crystal growth of the CIGS absorber layer, an Se layer was deposited on top of the SEL precursors, and RTP annealing was carried out by a 2-step process at 200 °C for 5 min and at 550 °C for 3 min. The stoichiometry of the CIGS film with Cu/(In+Ga) and Ga/(In+Ga) atomic ratios of 0.90 and 0.26, respectively, was obtained with the optimum thickness ratio of the Cu/In and Ga precursor layers. In grown CIGS film, the suppression of Se loss during the annealing is very important. A subsidiary quartz box was used for sustaining maintaining the Se vapors during the selenization process in order to prevent Se loss. The experimental results show that the method is effective for preventing Se loss without the use of toxic H2Se gas or any other Se sources. The obtained CIGS film was homogeneous, and the surface morphology was dense with quite a large grain size of about 2 μm.