Investigation of the effect of zinc precursors onto structural, optical and electrical properties of CBD deposited ZnS thin films

Zinc sulfide (ZnS) thin films were deposited onto microscopic silica slides through the cost-effective chemical bath deposition (CBD) method. The optimized bath parameters were: 25 ml of 0.1 M zinc precursors (ZnCl$_{2}$, Zn(CH$_{3}$COO)$_{2}$, ZnSO$_{4}$), 25 ml of 1 M thiourea and 3 ml of 3.75 M triethanolamine (TEA). The effects of different zinc precursors (ZnCl$_{2}$, Zn(CH$_{3}$COO)$_{2}$, ZnSO$_{4}$) on the growth mechanism of ZnS thin film were investigated using thermal, structural, morphological, optical and electrical studies. The XRD pattern has shown Miller indexing peaks corresponding to the hexagonal phase of as-grown ZnS thin film with the estimated grain size of 22 – 27 nm. The change in physical properties (weight loss) of ZnS powder as a function of temperature was recorded using thermogravimetry (TGA/DTA). Scanning electron microscopy (SEM) revealed the effect of ZnCl$_{2}$, Zn(CH$_{3}$COO)$_{2}$ and ZnSO$_{4}$ precursors on growth mechanism. UV/visible optical transmission/absorption spectra displayed the transmittance between 10 to 29 % of as-grown ZnS thin film with a band gap in the range of 4.10 – 4.25 eV. Photoluminescence (PL) analyses demonstrated broad blue emission around $\sim$ 459 nm was attributed to recombination of electron-hole pair from donor-acceptor trap levels to valance band. Raman spectra of ZnS powder prepared using different zinc precursors were also reported. The values of electrical parameters (resistivity, conductivity, activation energy, Hall coefficient, carrier concentration, mobility) were investigated using the two-point probe method and Hall-effect apparatus.