Research On The Growth Mechanism Of ZnS Thin Films Derived By CBD(Chemical Bath Depositon) Technique

ZnS thin films have a wide range of potential applications in various optoelectronic devices. ZnS is an excellent host material for electroluminescent phosphors and are being commercially used for electroluminescent(EL)displays. ZnS is also used as the n-type window layer for thin film heterojunction solar cells. ZnS thin films can be prepared by variety of techniques: chemical bath deposition, thermal evaporation, electron beam evaporation, sputtering, spray pyrolysis, and recently by the high temperature growth on to silicon substrates by pulsed laser depositon. This material is in greater demand in solar cells, and it requires a low cost production technology that will make the final product more affordable. Chemical bath deposition(CBD), a low cost growth technique, capable of producing good quality thin film semicongductors over large area and at low temperature, then becomes a suitable technology of choice.Here ZnS thin films were prepared by chemical bath deposition (CBD), using mixed aqueous solutions of zinc sulfate, thiourea, hydrazine hydrate and ammonia on glass sides, the as-deposited thin films were surface homogeneous. By adjusting the deposition conditions and various parameters, the thickness of the as-depositioned films can varied from a few nm to 200 nm.X-ray diffraction was used to characterize the microstructure of the films; optical properties were studied by spectrophotometric measurements; the thicknesses of the films were estimated using an elliptical polarimeter. In this paper, the effects of various technique parameters such bath temperature, pH values, ion concentrations, and deposition time on the optical properties, microstructures and appearance, and thinckness of the films were discussed, and at last the conclusion was got as well as the best CBD conditions and parameters. The as-fabrictaed films are microcrystallined with a sphalerite structure; the surface was compact, smooth and homogeneous. The films had very attractive optical, with the transmission above 75% over the visible range, the optical band gap in range of 3.85~3.95eV. Furthermore, the growth mechanisms of the reaction were investigated at the last part of this paper.