Post-growth annealing treatment effects on properties of Na-doped CuInS2 thin films

Structural and optical properties of Na-doped CuInS2 thin films grown by double source thermal evaporation method were studied. The films were annealed from 250 to 500 °C in a vacuum after evaporation. X-ray diffraction pattern indicated that there are traces of Cu and In6S7, which disappeared on annealing above 350 °C. Good quality CuInS2:Na 0.3% films were obtained on annealing at 500 °C. Furthermore, we found that the absorption coefficient of Na-doped CuInS2 thin films reached 1.5 × 105 cm−1. The change in band gap of the doped samples annealed in the temperatures from 250 to 500 °C was in the range 0.038–0.105 eV.