Influence of substrate activation process on structural and optical properties of ZnS thin films

• Substrate activation process is useful for the growth of ZnS thin films by chemical bath deposition method.
• Aluminum ions become the nucleation center for the active ingredients of the deposition solution.
• Carrier dynamics coincides with the build-up of the aluminum ions.
• Green emission is related to vacancies sulfur and impurities of aluminum ions.

ZnS thin films were deposited on glass substrates by a chemical bath deposition method using a substrate activation process in which aluminum ions become “contaminants” that act as a nucleation center for active components within the deposition solution. The structure and morphology results demonstrate that the films have a ZnS sphalerite crystal structure with a particle size less than 15 nm, and the films consist of small homogeneous grains. The effects of the substrate activation process on the band gap energies and donor-acceptor pair luminescence process were also investigated. A green emission centered at 502 nm was produced due to donor-acceptor transitions from the aluminum acceptor to the ionized and substitution aluminum centers (Al3+).