Electrodeposition of In:CdSe precursor thin films in aqueous electrolytes including different selenous acid concentrations as Se source

Abstract

In:CdSe precursor thin films were electrochemically grown on indium tin oxide (ITO) coated glass substrates at a constant potential of −0.95 V vs. Ag/AgCl reference electrode. Deposition solutions were composed of 10 mM CdCl2, 10 mM InCl3, 5–10 mM H2SeO3 as precursors, and 200 mM LiCl. The concentration of Se source (H2SeO3) was increased from 5 mM to 35 mM by a step of 5 mM. HCl was used for pH adjustment of the electrolytes. The uniform thin films are characterized by SEM-EDX, XRD, UV-VIS and Hall-Effect measurements. SEM studies show that the surface formations of In:CdSe deposits change depending on the Se content. For all deposits, XRD analyses confirm the formation of CdIn2Se4 with a tetragonal crystalline phase. Energy band gap of the films is calculated from Tauc equation using UV-VIS absorbance spectra. Energy band gaps are found to be between 1.98 eV and 2.23 eV. Hall-Effect measurements show all deposits exhibit n-type semiconductor character. The donor density changes between −1.3 × 1017 cm−3 and -4.1 × 1018 cm−3. The conductivity of the In:CdSe thin films decreases from 73.2 (Ωcm)−1 to 24.2 (Ωcm)−1 as the Se atomic percentage in the film increases.The mobility of the films increases with the increasing of Se atomic percentage. The reason of the increasing in mobility is most probably due to the decreasing in the donor concentration depending on Se percentage.