Chemical Bath Deposition of Cadmium Sulfide Thin Films. In Situ Growth and Structural Studies by Combined Quartz Crystal Microbalance and Electrochemical Impedance Techniques

Chemical bath deposition of layers, using the ammonia process, have been studied for the first time by combined in situ quartz crystal microbalance and electrochemical impedance techniques. Both allow monitoring of the growth kinetics, but an important result is that information about the covering properties of the film, its internal structure, and the evolution of this structure during the growth, have been obtained from combined experiments. The film is shown to have in general a duplex structure with an inner compact layer (only measured by capacitance) and an outer porous layer, growing at longer reaction times. The influence of the thiourea concentration on this structure is studied and discussed. Thiourea in excess is found to be very favorable for obtaining total coverage of the substrate with a minimum thickness of the film (≈30 nm on unactivated gold substrate), which is important for applications. A simple columnar growth model has been derived which accounts well for the experimental results.