Role of oxygen in enhancing N-type conductivity of CuInS2 thin films

Post-growth treatments in air atmosphere were performed on CuInS2 films prepared by the single-source thermal evaporation method. Their effect on the structural, optical and electrical properties of the films was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), optical reflection and transmission and resistance measurements. The films were annealed from 100 to 350 °C in air. The stability of the observed N-type conductivity after annealing depends strongly on the annealing temperature. Indeed it is shown that for annealing temperatures above 200 °C the N-type conductivity is stable. The resistance of the N-CuInS2 thin films correlates well with the corresponding annealing temperature. The samples after annealing have direct bandgap energies of 1.45–1.50 eV.