Effect of various deposition conditions on the electrical properties of LAO/STO hetero interfaces

We have examined the effects of partial oxygen pressure and laser energy density on the electrical transport properties of thin LAO films grown on (100) TiO2-terminated SrTiO3 substrates. Films were grown by pulsed laser deposition monitored by in-situ reflection high-energy electron diffraction (RHEED). Layer-by-layer growth, as indicated by clear RHEED oscillations, can be obtained in a wide range of oxygen partial pressures from 10(-6) to 5x10(-2) mbar. Transmission electron microscopy (TEM) analysis shows that the interface is coherent and atomically sharp for all deposition conditions. The STO substrate is oxygen self reduced at an oxygen pressure of 10(-6) mbar and the electrical properties of the interface are dominated by thed presence of oxygen vacancies. By increasing the oxygen pressure above 10(-4) mbar, the substrate itself is insulating but the interface still shows metallic conductivity. However, the interface becomes insulating at an oxygen pressure of 5x10(-2) mbar. We also found that the interface exhibits insulator-to-metal transition by changing the laser fluence during the deposition of the film. The interface prepared at 5x10(-2) mbar shows metallic conductivity at high fluence, above 3.5 J/cm(2)