Physical and electrochemical properties of electrodeposited undoped and Se-doped ZnS thin films

In this paper, we report the effect of various Se-dopant concentrations on the structural, morphological, optical, electrical, and electrochemical properties of ZnS thin films. Undoped ZnS and Se-doped ZnS thin films were prepared using a three-electrode electrochemical cell. The indium doped tin oxide glass substrate (ITO) was used as the cathode. The anode and reference electrodes were a platinum wire and a saturated calomel electrode (SCE), respectively. An aqueous solution containing ZnCl2 and Na2S2O3 was used as the main solution. Different concentration of the SeO2 solution was added to the main solution to obtain Se-doped ZnS thin films. All deposited films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), photoluminescence (PL), UV-Vis spectroscopy, and electrochemical impedance spectroscopy (EIS). The XRD patterns exhibited forming cubic ZnS for all samples. FESEM images showed big grains about 150-450 nm in a background phase for all samples. PL and UV-Vis analysis examined the optical properties of deposited films. The band gap energy (E-g) of undoped ZnS was estimated to be 3.93 eV, which was reduced to 3.16 eV after Se-doping. Mott-Schottky analysis showed that the carrier concentration of undoped ZnS increased from 6.04 x 10(19) cm(-3) to 60.01 x 10(19) cm(-3), after Se-doping.