Electronic Transport Properties of the PrAlO$_3$/SrTiO$_3$ Interface: Effects of Oxygen Pressure

We explored the electronic and magnetic behavior of epitaxial PrAlO$_3$ films on TiO$_2$-terminated SrTiO$_3$ (PAO/STO) substrates grown by pulsed laser deposition at various oxygen pressures. We report structural (x-ray and AFM), electronic (van der Pauw resistivity, magnetoresistance (MR), and Hall effect), and magnetic data for PAO films grown in 10$^{-3}$--10$^{-6}$ torr O$_2$. Resistivity data exhibit metallic behavior from 300 K down to 100--150 K (75 K; 40 K) for the interface grown in 10$^{-3}$ (10$^{-4}$; 10$^{-5}$) torr O$_2$, and semiconducting behavior below that. One 10$^{-3}$ torr O$_2$ interface shows typical behavior for current parallel to atomic terraces, and a resistance anomaly in the range 50--100 K for current perpendicular to step edges. MR data for all 10$^{-3}$--10$^{-4}$ torr O$_2$ samples show a small ($\le$0.5\%) positive MR at low fields, and a larger negative MR (2--30\%) at high fields; for 10$^{-5}$ torr O$_2$, the MR is positive up to 9 tesla. Sheet resistivity for the 10$^{-6}$ torr O$_2$ interface is anomalously low, suggesting a thick conducting layer. Hall effect data exhibit several variations in the carrier density. We discuss these data considering intrinsic charge transfer, oxygen vacancies and interstitials, and cation interdiffusion.