Structural and transport properties of SrRuO3 thin films grown by MOCVD on (0 0 1) SrTiO3 substrates: The role of built-in strain and extra phases

Pure SrRuO3 (SRO) thin films and SRO thin films containing the extra metallic phases Ru, RuO2 and Sr3Ru2O7 were deposited by MOCVD on (0 0 1) SrTiO3 substrates under different conditions (Ru/Sr and Ar/O2 ratio in the gas phase, substrate temperature, supersaturation). The single-phase compressively-strained SRO film is of high structural quality and shows a ferromagnetic transition at a suppressed Curie temperature (Tc) of about 142 K and low electrical resistivity (230 μΩ cm). Under certain deposition conditions Ru and RuO2 extra phases form leading to a reduced room temperature resistivity of 100 μΩ cm. On the other hand, the presence of Sr3Ru2O7 increases the resistivity to 385 μΩ cm. We have observed that the existence of the extra phases caused a slight shift of Tc towards the bulk value, while relaxation of the lattice strain resulted in increase of Tc to 160 K. The deviation from the stoichiometric composition in films with extra phases is also confirmed by the residual electrical resistivity ratio. On the other hand, the pure SRO films, the compressively strained and the plastically relaxed exhibit a stoichiometric ratio.