Interface-charge-coupled polarization response model of Pt-BaTiO3-ZnO-Pt heterojunctions: Physical parameters variation
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1074-I01-11
Interface-charge-coupled polarization response model of Pt-BaTiO3-ZnO-Pt heterojunctions: Physical parameters variation Venkata Voora1, Tino Hofmann1, Ann Kjerstad1, Matthias Brandt2, Michael Lorenz2, Marius Grundmann2, and Mathias Schubert1 1 Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588 2 Institut für Experimentelle Physik II, Universität Leipzig, Leipzig, Germany ABSTRACT Heterojunctions composed of wurtzite-structure (piezoelectric) ZnO and perovskitestructure (ferroelectric) BaTiO3 are very interesting because of the coupling effects between the non-switchable ionic charge of wurtzite-structure and electrically switchable lattice charge of pervoskite structure at their common interface. In this paper we report the variations in the overall electrical properties of the ZnO-BaTiO3 heterostructure as a function of different physical attributes by using our previously reported physical model approach. This numerical model analysis helps us to prepare the samples by using pulsed laser deposition with specific electrical properties. This study is also useful for the future device applications. INTRODUCTION BaTiO3 (BTO) has perovskite structure, having electrically reversible spontaneous polarization. BTO is well investigated due to its piezoelectric, pyroelectric, and ferroelectric properties [1-3]. ZnO possesses wurtzite structure, having fixed irreversible lattice charge. ZnO has received increased attention due to many attractive properties such as wide transparency, and the strongly excitonic direct fundamental electronic band gap transition in the ultra violet region [4]. Heterostructures [5] composed of ZnO and BTO thin films are interesting because of the coupling effects between the electrically switchable lattice charge of BTO and the nonswitchable lattice charge of ZnO. The non-switchable lattice charge of ZnO biases and thereby influences the switching behavior of the ferroelectric polarization charge in the adjacent BTO thin film [6]. Thin-films Pt-BTO-ZnO-Pt heterostructures were grown by using pulsed laser deposition (PLD). With the ZnO layer controlled to be slightly n-type conductive, and the BTO thin film to be highly resistive, the thin film multilayers thereby form metal-ferroelectric-semiconductor (MFS) structures. We observed previously pinning of the ferroelectric polarization in the BTO thin films by the cladding ZnO thin films, and rectifying behavior in electro-optic Raman scattering and Sawyer-Tower circuit measurements, respectively [6-9]. In the Sawyer-Tower experimental output, asymmetric polarization hysteresis behavior was observed. We developed a dielectric continuum model to describe the asymmetric polarization hysteresis behavior and thereby confirmed the influence of the lattice charge of ZnO on the BTO switchable ferroelectric charge [10]. This model is based on the approaches discussed previously for description of metal-ferroelectric-metal (MFM) electric hysteresis properties [11-14]. Concordant with our experimental observa
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