The Influence of Precursor Ratio on Structure, Morphology and Resistivity of Thin ZnS Films Sprayed by Improved Method

Abstract

Thin ZnS films were prepared by improved spray pyrolysis (ISP) method for precursor (Zn/S) ratios (1:1) to (1:6) in the initial solution. The ISP parameters such as carrier gas flow rate, solution flow rate and substrate temperature were controlled with an accuracy of \({\pm0.25\,{{\rm lpm}},\, \pm1\,{{\rm ml/h}}}\) and \({\pm1\,^{\circ}{{\rm C}}}\), respectively. The solution was sprayed in a pulse mode. The chemical and physical properties for these thin films were investigated as a function of solution precursor ratio. The films were fairly smooth with satisfactory crystallinity. The films have exhibited a polycrystalline cubic structure. A gradual increase in (S/Zn) atomic ratio from 0.82 to 1.01 with the increase in solution precursor ratio was observed. The properties such as crystal size, texture coefficient, band gap, grain size and electrical resistivity for thin ZnS films showed a gradual improvement with the increase in their (S/Zn) atomic ratio. The behavior of non-stoichiometric (zinc excess) thin films was like n-type extrinsic semiconductors. The thin film (1:6) have the larger crystal size of 5.59 nm, grain size of 72 nm, band gap of 3.634 eV and electrical resistivity of \({6.85\times10^{6} \,\Omega\,{{\rm cm}}}\). These features of ISP-prepared thin ZnS films make the films more appropriate for optical and photovoltaic applications.