Significant effect of substrate temperature on the phase structure, optical and electrical properties of RF sputtered CIGS films

This work studied the effect of substrate temperature on the phase structure, optical and electrical properties of the one-step radio frequency sputtered Cu(In,Ga)Se2 (CIGS) thin films. X-ray diffraction (XRD) analysis revealed that all the deposited CIGS films are chalcopyrite phase with polycrystalline structure. The films deposited beyond the substrate temperature of 350 °C show (1 1 2) prefer orientation. Raman spectra reveal that the 150 °C deposited CIGS film coexists with Cu2−xSe phase and the 500 °C deposited film contains ordered defect compound (ODC) phase. With the increase of substrate temperature, energy band gap of the CIGS film increase from 0.99 to 1.27 eV. Films deposited at higher temperature exhibit larger electrical conductivity. Conductivity of the CIGS films is dominated by “variable range hopping” mechanism. The disorder in our CIGS the films is associated with the formation of intrinsic defects such as VSe and InCu for their low formation energy.