Surface Photovoltage Spectroscopy for the Investigation of Perovskite Oxide Interfaces
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0902-T07-05.1
Surface Photovoltage Spectroscopy for the Investigation of Perovskite Oxide Interfaces Elke Beyreuther1*, Stefan Grafström1, Christian Thiele2, Kathrin Dörr2, and Lukas M. Eng1 Institute of Applied Photophysics, Technische Universität Dresden, D-01062 Dresden, Germany 2 Institute for Metallic Materials, IFW Dresden, D-01171 Dresden, Germany *corresponding author: phone +49 351 46339191, fax +49 351 46337065, e-mail: [email protected] 1
ABSTRACT In the present study, we comparatively investigate the distribution of electronic interface states of three different perovskite oxide interfaces, formed by epitaxial thin films of La0.7Sr0.3MnO3 (LSMO), La0.7Ca0.3MnO3 (LCMO), and La0.7Ce0.3MnO3 (LCeMO) on SrTiO3(100) substrates, in the as-prepared state as well as after an annealing procedure. We find that annealing significantly reduces the number and density of interface trap states. Two different experimental realizations of the surface photovoltage spectroscopy (SPS) technique were employed: an approach based on Xray photoelectron spectroscopy (XPS), as well as a capacitive method. The advantages and limitations of both methods are critically discussed. INTRODUCTION Among the functional multicomponent oxides which are currently considered as the materials of choice for the next generation of electronic devices, several groups have attracted special interest, e.g. the mixed-valence manganites, which have recently been reviewed by several authors [1-4]. They exhibit a wide variety of magnetic, crystallographic, and electronic phases, as well as different intriguing phenomena such as the colossal magnetoresistance (CMR) effect or a high spin polarization of the conduction band. The progress in the field of oxide electronics is decisively determined by the quality of the oxidic interfaces, because the functional properties of those compounds are crucially influenced by the distribution of intrinsic and defect-related electronic interface states. Not for nothing is the outstanding success of silicon mainly based on the high achievable quality of the Si/SiO2 interface. Hence, for the analysis of electronic interface properties, there is a demand for a technique that is sensitive to interface trap states, apart from conventional methods such as deep-level transient spectroscopy (DLTS) or capacitance-voltage spectroscopy. The latter require a certain carrier concentration of the substrate, which is lacking in insulating high-gap materials such as SrTiO3 (STO) [5-7]. Surface photovoltage spectroscopy (SPS), which is based on the phenomenon of surface photovoltage (SPV), has been shown to be an effective technique for determining the surface or interface electronic structure of semiconductors [8]. Especially for the study of high-bandgap materials, to which perovskite oxides such as the titanates can be assigned, SPS is superior to other spectroscopy methods [5-7]. The implementation of SPS may be carried out in several ways such as the photoassisted Kelvin probe technique, the capacitive detection of the displacement c
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