Dependence of the electrical and optical behaviour of ITO–silver–ITO multilayers on the silver properties

ITO–metal–ITO (IMI) multilayers and ITO single layers were prepared by DC-magnetron sputtering with different oxygen concentrations of the sputtering atmosphere during ITO deposition, and different substrate temperatures during a subsequent annealing treatment in vacuum. The intermediate metal layer consisted of 10 or 30 nm silver. Electron concentration and mobility of the Ag partial layer were determined from measurements of the electrical resistivity and by evaluating the complex dielectric function, obtained from optical transmission and reflectance. Microstructure and purity were studied with X-ray diffraction (XRD) and with X-ray photo electron spectroscopy (XPS) depth profiles. With a 10-nm intermediate silver layer an IMI sheet resistance of 4.7 Ω/□. was achieved. The Ag films had almost bulk electron concentrations but reduced electron mobilities. The ITO crystallinity in IMI systems influenced the microstructure and purity of the Ag layer. Minimum Ag resistivity and optimum Ag purity were obtained by ITO deposition under stoichiometric conditions and annealing in vacuum at 300°C. An increase of the ITO lattice constant is indicative that as-deposited IMI multilayers prepared with ITO deposition at high oxygen concentration or under stoichiometric conditions are associated with stress. The presence of the Ag layer impedes the lattice relaxation upon annealing.