Investigation of structural, optical and electrical properties of precursor and annealed CdSe thin films produced by electrodeposition method

Cadmium selenide (CdSe) thin films are deposited on indium tin oxide (ITO) coated glass substrates by co-electrodeposition technique. An aqueous deposition solution is prepared using water soluble molecular sources such as 10 mM CdCl2, 20 mM H2SeO3, 200 mM LiCl and five drops of HCl. CdCl2 and H2SeO3 are respectively used as Cd and Se molecular sources. According to the SEM images, the surface of CdSe thin film changes from smooth to crystalline appearance with spherical formations due to the annealing. Cd/Se ratio of precursor and annealed CdSe materials is respectively determined as 1,07 and 1,04. XRD studies confirm that the CdSe films have polycrystalline nature. Precursor CdSe film exhibits cubic phase of CdSe, while annealed CdSe film includes both hexagonal phase of CdSe and cubic phase of CdO. Optical energy band gap of the CdSe material increases from 1,64 to 1,71 eV due to the annealing procedure. Dispersive refractive index varies between 2,0 and 3,3. Calculations based on the Mott-Schottky (MS) measurements show that precursor and annealed CdSe thin films have 1,72x1016 and 3,65x1017 cm-3 carrier concentration, respectively. Produced CdSe thin films have n-type conductivity. In this study, it is also presented electronic energy structures of the CdSe thin films by using Mott-Schottky and Tauch's approximations. An equivalent circuit is fitted to the Nyquist data of the CdSe materials. According to the fit results, circuit elements in the aforementioned model are used to explain carrier transport facilities in the CdSe/electrolyte interface.