ZnS thin buffer layers were prepared by chemical bath deposition (CBD) process. The structures and optical properties of the films were studied systematically based on the chemical reaction principle. The results demonstrated that the thickness of ZnS film increased with the increase of deposition time

while the optical transmittance and the band gap decreased. The minimum E

g

was determined to be 3.74 eV. The surface roughness of the as-deposited films remained a low level

of which value remained between 6~9 nm. As the concentration of the reactant increased

the optical transmittance increased first and then decreased. When the concentration of the reactants were too high or too low

the deposition reaction shifted to homogeneous reactions and impurities emerged on the surface of the films

resulting in inhomogeneous films. The optimized concentrations of ZnSO

4

SC(NH

2

)

2

and NH

3

·H

2

O were 0.03

0.4

4.0 mol/L

respectively. The single-phased ZnS films were homogeneous and compact with the optical transmittance over 70% at the wavelength of 450~900 nm.