Influence of Oxygen Content on the Electronic Properties of the PrAlO 3 /SrTiO 3 Interface
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Influence of Oxygen Content on the Electronic Properties of the PrAlO3/SrTiO3 Interface Shirin Mozaffari1, Mark C. Monti1, Samaresh Guchhait2, Jeremy W. Paster1, Daniel M. Tennant1 and John T. Markert1 1 Physics Department, The University of Texas at Austin, 2515 Speedway, C1600, Austin, TX 78712, U.S.A. 2 Micoelectronic Research Lab, The University of Texas at Austin, 10100 Burnet Rd, Austin, TX 78758, U.S.A. ABSTRACT We have investigated the effect of oxygen pressure during growth (PO2) on the electronic and magnetic properties of PrAlO3 films grown on TiO2-terminated SrTiO3 substrates. The films are smooth, with flat terraces. Resistivity measurements show an increase in the sheet resistance as PO2 is increased from 10–3 to 10–4 torr, with an usual peak as a function of temperature for the sample grown in higher oxygen pressure. We measured a moderate positive magnetoresistance (MR) at low magnetic fields that evolves into a larger negative MR at high fields, for both PO2 samples. Hall effect data exhibit a complex temperature dependence that suggests a compensated carrier density. We observe behavior consistent with two different types of carriers at each of the two different interfaces. INTRODUCTION It has been a decade since a two-dimensional electron gas (2DEG) at the interface of epitaxially grown LaAlO3 (LAO) on TiO2-terminated SrTiO3 (STO) was discovered [1]. During this time, there have been numerous studies aimed at understanding the origin of conductivity at the interface. In addition to the formation of the 2DEG, the interface has displayed magnetic scattering [2], electric-field-tuned metal-insulator transitions [3], and superconductivity [4]. In addition to an intrinsic charge-transfer at the interface, two other mechanisms have been proposed to explain the origin of the conductivity. These involve doping, either by the interdiffusion of La/Sr atoms [5] at the interface, or by the creation of oxygen vacancies in the SrTiO3 [6] substrate during the deposition process. Similar 2DEGs have also been reported to form at the interface of STO with some other rare-earth aluminates and gallates [7], systems where the film layers have a polar nature. We are exploring the electrical and magnetic properties of one of these interfaces, PrAlO3/SrTiO3, to investigate the importance of the nature of the overlayer in tuning the electrical properties. PrAlO3 (PAO) in bulk form has mainly been investigated for its interesting structural phase transitions below room temperature, which are absent in other rare-earth aluminates. At room temperature, PrAlO3 has a rhombohedral structure which transforms to an orthorhombic structure upon lowering the temperature to about 205–225 K, and to a monoclinic structure at about 151–175 K [8]. The structure becomes more nearly tetragonal as the sample is further cooled, but high resolution diffraction confirms that the symmetry remains monoclinic down to the lowest measured temperature. In this study, we synthesized thin films of PAO by pulsed laser deposition (PLD) on TiO2-terminate
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