Properties of CuS thin films treated in air plasma

Copper sulfide thin films were grown by chemical deposition and post treated in air plasma during 20 min. Air plasma was generated by alternating current discharge at a pressure of 4 × 10² Pa. The power discharge was maintained at an output of 220 V and a current of 0.2 A. Thermal annealing at 300 °C was performed for comparison. X-ray diffraction shows that plasma treatment results in phase transformation of Cu₃₉S₂₈ (as grown) to CuS (treated by plasma). The copper lost is confirmed by X-ray fluorescence. No significant change in the optical band gap was observed due to plasma action. In addition, the electrical conductivity increases in one order of magnitude. On the other hand, the samples under plasma condition show a parallel growth to the substrate and an increase in the surface uniformity. The plasma etching removes copper due to its affinity with oxygen to form CuO, as is corroborated by optical emission spectroscopy.