Magnetic Field Dependence of the Schottky Barrier Height at Manganite/Titanate Heterointerfaces

This is a copy of the slides presented at the meeting but not formally written up for the volume. The interface electronic structure of transition metal oxides has attracted considerable attention in recent years. Given the versatile physical properties of these materials, and the interest in developing novel functional devices unattainable by conventional semiconductors, understanding interface barrier formation and control is a central issue. Among various interface structures, single interface junctions are the simplest structure for their study, and their transport properties can provide much of the essential information for depiction of the interface electronic structure. Recently, magnetic field dependent current-voltage (I-V) and capacitance-voltage (C-V) characteristics were reported for a junction between oxygen deficient manganite (La0.7Sr0.3MnO3-a) and 0.01wt% Nb doped SrTiO3 (Nb:STO). By contrast, no magnetic field dependence was observed for the stoichiometric junction (La0.7Sr0.3MnO3 / Nb:STO) [1]. La0.7Sr0.3MnO3-a is a ferromagnetic metal with a Curie temperature lower than the stoichiometric counterpart, and Nb:STO is an n-type band semiconductor. The magnetic field dependence of the I-V and C-V are contrary to the expectation from the Zeeman effect [1]. To elucidate the origin of the magnetic field dependence observed, we used internal photoemission (IPE) to directly probe the evolution of the Schottky barrier height. In this technique, the reverse junction current is monitored while the sample is illuminated with monochromatic light of varying wavelength. IPE is a direct, reliable method for the determination of Schottky barrier heights since the measurement is free from external electric field, eliminating any complexity associated with bias dependent effects observed in the case of I-V and C-V. In addition, its compatibility with external magnetic field makes this method especially desirable for investigating interface electronic structures involving magnetically sensitive materials. Junctions with different oxygen stoichiometry were grown by pulsed laser deposition of a La0.7Sr0.3MnO3 target on Nb:STO substrates, and their I-V, C-V and IPE characteristics were measured under magnetic field. Magnetic field dependence was observed by all three techniques for La0.7Sr0.3MnO3-a / Nb:STO, whereas they were field independent for La0.7Sr0.3MnO3 / Nb:STO. In La0.7Sr0.3MnO3-δ / Nb:STO, the barrier height determined from IPE measurements significantly decreased with magnetic field, which is consistent with the I-V and C-V results. The origin of the magnetic field dependent Schottky barrier height will be discussed. [1] N. Nakagawa et al., App. Phys. Lett. 87, 241919 (2005).