A new chemical bath deposition method for fabricating ZnS, Zn(OH)2, and ZnO thin films, and the optical and structural characterization of these materials

Abstract

ZnS thin films were deposited on glass and polymer substrates using a reaction between thiourea and a stable zinc complex, Zn(en)3SO4 (en: ethylenediamine) or Zn(trien)(ClO4)2 (trien: triethylenetetraamine), in alkaline media. In a weak alkaline solution, Zn(OH)2 films were formed. The deposition reactions were controlled by the supply of sulfide ions from thiourea at a suitable rate in alkaline media and by the dissociation of free-metal ions from the metal complex used, the stability of which defined the free Zn2+ concentration throughout the reaction. The ZnS films showed emission peaks at ca. 450 and 485 nm, and the transmittance decreased with decreasing wavelength of the incident light in the visible region of the spectrum. ZnO thin films were deposited by decomposition of Zn(en)3SO4 in the presence of Cu(en)2(ClO4)2 and thiourea; the copper(II) complex catalyzes this reaction. The ZnO films exhibited an emission peak at ca. 420 nm, and the absorbance was constant in the visible region of the spectrum. The scanning electron microscope images showed the formation of a fairly uniform surface with fine crystalline particles.