Optical Properties of Highly Conductive SrMoO 3 Oxide Thin Films in the THz Band and Beyond
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Optical Properties of Highly Conductive SrMoO3 Oxide Thin Films in the THz Band and Beyond Stefan Regensburger1 · Mahdad Mohammadi2 · Arslan A. Khawaja1 · Aldin Radetinac2 · Philipp Komissinskiy2 · Lambert Alff2 · Sascha Preu1 Received: 6 April 2020 / Accepted: 30 April 2020 / © The Author(s) 2020
Abstract Strontium molybdate (SrMoO3 ) thin films are grown epitaxially by pulsed laser deposition onto gadolinium scandate (GdScO3 ) substrates and characterized in the terahertz (THz) and visible part of the electromagnetic spectrum. X-ray diffraction measurements prove a high crystallinity and phase-pure growth of the thin films. The high-quality SrMoO3 thin films feature a room temperature DC conductivity of 1 around 3 μm . SrMoO3 is characterized in the THz frequency range by time domain spectroscopy. The resulting AC conductivity is in excellent agreement with the DC value. A Lorentz-Drude oscillator approach models the THz and visible conductivity of SrMoO3 very well. We compare the results of the SrMoO3 thin films to a standard, 1 . The comparison sputtered gold film, with a resulting THz conductivity of 8 μm demonstrates that oxide thin film–based devices can play an important role in future THz technology. Keywords SrMoO3 · GdScO3 · Perovskite · Conductive thin film · THz spectroscopy
1 Introduction The vast variety of functional properties make the material class of perovskite oxides and related structures predestined for realization of all-oxide epitaxial metalinsulator-metal (MIM) heterostructures in high-frequency microelectronic devices.
This research is supported by Profilbereich PMP from TU Darmstadt. Stefan Regensburger
[email protected] 1
THz Devices and Systems, Technische Universit¨at Darmstadt, Darmstadt, Germany
2
Institute of Materials Science, Technische Universit¨at Darmstadt, Darmstadt, Germany
International Journal of Infrared and Millimeter Waves
The epitaxial nature of such heterostructures allows lower defect densities and therefore enhanced functional properties in comparison with polycrystalline thin films. Interface engineering at the atomic level and precise stoichiometry tuning of the layers in MIM varactor heterostructures enable improved functional properties of the materials such as high electric conductivity of oxide electrodes and high tunability of the dielectrics [1, 2]. Moreover, all-oxide epitaxial MIM heterostructures, including structurally compatible high-temperature superconductors, can be used for realization of novel thermally tuned THz metamaterials [3, 4]. For all-oxide MIM heterostructures, the cubic perovskite oxide SrMoO3 (SMO) is the material with the highest conductivity of any perovskite reported so far [1, 5]. The partially reduced Mo4+ B-site cation provides a high concentration of charge 1 carriers in the material, resulting in a room temperature conductivity of 20 μm for an SMO single crystal [6]. This value surpasses even conventional electrode metals like platinum. So far, SMO thin films have been characterized in the DC, micr
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