engleski

Structural analysis of ZnO-SnO double layer by XRD, vibrational spectroscopy and microscopy

Zinc oxide (ZnO) was used as a protecting layer for SnOx thin film during the deposition of thin film Si solar cells by plasma enhanced chemical vapour deposition in hydrogen/silane gas mixture. ZnO films were catholically deposited on a conductive glass substrate covered with SnO2 as cathode by a potentiostatic method. SnO2 films were prepared by spray pyrolisis using 0.1 M water solution of SnCl2 with complexes of NH4 F. The electrolysis takes place in a simple aqueous 0, 1M zinc nitrate [Zn(NO3 )2 ] solution with pH about 6, maintained at 650 C temperature. A simple apparatus was used for electrochemical deposition that consisted of a thermostat, a glass cell with solution, two electrodes (cathode and anode) and a standard electrical circuit for electrolysis. The anode was zinc of 99, 99% purity. After the deposition, bi-layer and single layer films were exposed to the hydrogen plasma and effects were studied. The structure of the films was studied by X-ray diffraction measurements (XRD), Raman and infra red spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). X-ray spectroscopy of the studied films showed polycrystalline structure of both films. Rietveld refinement yields to average size of ZnO crystals of about 70 nm and the substrate material SnO2 of about 20nm. The XRD spectrum indicates a strong ZnO peak with a (0002) preferential orientation. After plasma treatment, films showed increased average strain, possibly due to diffusion of hydrogen into the films. SEM and AFM micrographs showed a polycrystalline structure, on which one could see the surface of small rounded grains with diameters between 100 and 200 nm, depending on electro deposition potential, consistent with XRD. After exposure to the hydrogen plasma, additional craters appeared, possibly as a consequence of blistering effects. Raman and IR spectroscopy showed that initial films are stehiometric which is changed in the case of SnOx after plasma treatment. ZnOx films did not show chemical changes after the same treatment in hydrogen plasma, within experimental error.

ZnO; SnO; bi-layer

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