Influence of implantation induced Ni-doping on structural, optical, and morphological properties of nanocrystalline CdS thin films

Ni-doped CdS thin films were prepared by 90 keV Ni⁺ implantation at room temperature. Ni-ion implantation induced modifications in structural, optical, and morphological properties are studied for a wide range of impurity concentrations (1.86–10.19 at.%). Addition of Ni⁺ ions does not lead to any structural phase transformation or formation of metallic clusters or secondary phase precipitates. However, it induces structural disorder leading to a reduction in the optical band gap from 2.39 to 2.28 eV following Ni implantation up to 3 × 10¹⁶ ions cm⁻². This is addressed on the basis of band tailing due to the creation of localized energy states and implantation induced grain growth. Moreover, Ni-doping is found to modify the luminescence properties by creating shallow acceptor states.