Study of a nanostructured compound based on II-VI semiconductors (ZnS).

Abstract

This thesis deals with the elaboration and characterization of zinc sulfide (ZnS) nanostructures for photovoltaic applications. We used the electrochemical deposition method to synthesize these films, and this, for its simplicity and low cost. The deposit solution is composed of zinc sulfate and sodium thiosulfate (Na2S2O3) as sources of Zn and S, respectively. This work is devised on two part. First, the samples were prepared by varying several parameters such as zinc concentration, pH, deposition potential and time deposition. The obtained nanostructures were subjected to various characterizations such as electronic (Mott-Schottky), morphological (SEM, AFM), Structural (XRD) and optical properties (UV-Vis). The Mott-Schottky measures showed that the films have an n-type conductivity when the carrier concentration and flat band potential was strongly depend on the different parameters. The morphological characterization of the samples by AFM and SEM showed a significant change of the with topography different parameters. The structural analysis shows that the obtained films are monocrystalline, they exhibit a zinc blend structure. The preferential orientation is strongly related to the experimental parameters. Studied at the end of this part the optical results show a lower transmittance. The second part is devoted to the doping of ZnS nanostructures by rare earths (Er, Sm). An improvement of optical properties (transmittance 80%) was obtained when we increase the dopants concentration and the optical band gap increases after doping from 3.54 to 3.8 eV for both dopants. The time-resolved photoluminescence decay were used to determine the charge carrier transfer (life time) of ZnS with the Er and Sm doping.