Dramatic change of electrical properties in La-Ba-Mn-O thin films prepared using bias sputtering

Polycrystalline La-Ba-Mn-O thin films have been grown using rf magnetron sputtering on Si(100) substrates from a stoichiometric La0.7Ba0.3MnO3 target. Four films were grown with substrate biased such as -5, -10, -15, and -25 V and compared with the film grown with grounded substrate. Bias effects on the stoichiometry and physical properties of the films are studied. The dc resistivity was measured in the temperature range from 85 to 300 K for the films with substrate bias of 0, -5, -10, -15, and -25 V. The magnetoresistance was measured in the magnetic field of 0-10 000 Oe and at 77 K. The film with grounded substrate showed semiconductor behavior (dρ/dT<0) over the whole temperature range. The films with biased substrate, however, showed the maximum resistance at each metal-insulator transition temperature TMI. In order to find out the origin of the extreme change of electrical resistivity, x-ray photoemission spectroscopy (XPS) and x-ray diffraction (XRD) measurements were carried out. From the analysis of XPS and XRD data, bias sputtering increased La and Ba concentration in the La-Ba-Mn-O thin film and led to an increase of Mn-O-Mn bond angle. It changed films from semiconductor behavior to metal-insulator transition behavior