Electrodeposition of PbS, PbSe and PbTe thin films: Dissertation

Lead chalcogenides (PbS, PbSe, PbTe) are narrow band gap semiconductors which are largely used in infrared applications. In the present study lead chalcogenide thin films were deposited electrochemically from aqueous solutions. Two different electrodeposition methods were used; PbSe and PbTe thin films were prepared at constant potential while PbS was deposited by cycling the potential. Chemical and physical properties of the films were examined by various techniques, and their electrical properties were studied as well. PbSe and PbS thin films were found to be stoichiometric whereas PbTe thin films contained an excess of Te. The films contained water as an impurity. All the films had polycrystalline, randomly oriented cubic structure. After annealing the films showed p-type conductivity. The annealing at 100 °C did not affect much the resistivities of PbS and PbTe which remained between 0.5-10 W cm but the resistivity of PbSe films increased to 1-60 kW cm. All films showed IR activity. Electrodeposition mechanisms of PbSe, PbTe and PbS thin films and electrochemistry of the related precursors were studied by means of the electrochemical quartz crystal microbalance (EQCM) combined with cyclic voltammetry. Both film growth and EQCM studies showed that the electrodeposition of PbSe and PbTe occurs by the induced codeposition mechanism, where Se (or Te) is deposited first and induces the reduction of lead ions to form PbSe (or PbTe) so that this occurs at more positive potential than where lead alone would be deposited. Electrodeposition of PbS, on the other hand, turned out to be complicated including several simultaneous processes.