Growth by rf magnetron sputtering of electron-doped Sr1−xCaxCuO2−δ infinite-layer films and their structural properties

Abstract

Thin films of the infinite-layer (IL) compound, Sr1−xCaxCuO2−δ (x = 0, 0.3 and 0.4), have been prepared by off-axis radio-frequency (rf) magnetron sputtering on SrTiO3 (100) and KTaO3 (100). The c-axis lattice parameter of the IL phase shrinks with the increase of the substrate temperature and with the decrease of oxygen partial pressure, whereas the a-axis lattice parameter expands accordingly. This behaviour suggests the availability of the incorporation of oxygen vacancies in the CuO2 planes and the mechanism of electron doping. For the lower doping level, for example, when the doping level is less than 0.08, the temperature dependence of resistivity shows insulating or semiconducting behaviour. On the other hand, the large amount of in-plane oxygen deficiencies will also lead to a high degree of disorder in the CuO2 planes, especially when the in-plane oxygen vacancies are larger than 10%. This will result in a variable range hopping transport mechanism. Moreover, we have demonstrated that electrons can be doped in the IL phase by reducing the oxygen content.