Transport properties and superconductivity of lanthanum-doped strontium titanate thin films grown by laser ablation

We present studies on superconducting La-doped strontium titanate thin films grown by laser ablation. Results of depletion effects on Nb-doped strontium titanate films through metal-semiconductor Schottky junctions are presented. Limitations at low temperatures of depletion effects lead us to the study of La-doped strontium titanate thin films. We present transport properties of these films and the dependence of these properties on oxygen pressure during growth. One important result obtained was the finding of high mobilities and carrier concentrations at high oxygen pressures during growth. These films show also a superconductive transition below 1 K, and we show the phase boundary for La-doped strontium titanate thin films grown at different oxygen pressures and on three different substrates: LaAlO₃, NdGaO₃ and SrTiO₃. Measurements of the upper critical field allow us to obtain diffusion constants and these are compared to normal-state transport properties. The tolerance of La-doped strontium titanate thin films to oxygen allow for the fabrication of bilayered La-doped SrTiO₃/undoped SrTiO ₃ with depletion effects at low temperatures.