Ferroelectric monoclinic phases in strained K0.70Na0.30NbO3 thin films promoting selective surface acoustic wave propagation

Helden, Leonard von; Schmidbauer, M.; Liang, Sijia; Hanke, M.; Wördenweber, R.; Schwarzkopf, Jutta

doi:10.1088/1361-6528/aad485

Cited by 19 publications

(13 citation statements)

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“…No contrast fluctuations are observed within the film indicating homogeneous and coherent film growth. This is verified by high-resolution transmission electron microscopy (HRTEM) measurements, presented in Figure 2b, which also display an atomically sharp SrSnO 3 /NdScO 3 interface seen along [1][2][3][4][5][6][7][8][9][10] direction and no extended defects in the SrSnO 3 film. On the other side, a strong dark contrast occurs at the interface between the undoped BaSnO 3 and SrSnO 3 layers and a large amount of threading dislocations is visible in the BaSnO 3 film (Figure 2a), which lead to the formation of strong strain fields at the BaSnO 3 /SrSnO 3 interface.…”

Section: Introductionsupporting

confidence: 62%

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Confinement of Electrons at the LaInO₃/BaSnO₃ Heterointerface

Pfützenreuter

Kim

Cho

et al. 2022

Adv Materials Inter

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temperature mobility of 320 cm 2 V −1 s −1 at a carrier density of 8.0 × 10 19 cm −3 in a bulk single crystal. [8] Furthermore, BaSnO 3 is a transparent wide bandgap semiconductor with a bandgap of 3.1 eV, which makes it suitable for high power applications like field effect transistors (FET). [9] To exploit the full potential of a FET, a 2D electron gas (2DEG) with high carrier density and mobility is highly desirable. The formation of a 2DEG at the LaInO 3 /BaSnO 3 interface was found and studied experimentally by Kim et al. in 2016 and thereafter [10,11] and has been theoretically investigated using several models. [12][13][14] Analysis of the Seebeck coefficient as well as Poisson-Schrödinger simulations suggested a thickness of ≈1 nm for the 2DEG. [14] Recently, another similar polar interface, namely LaScO 3 /BaSnO 3 , has been investigated. [15,16] In this paper we report on the epitaxial growth of LaInO 3 / BaSnO 3 heterointerfaces using a SrSnO 3 buffer layer on NdScO 3 substrates. We provide clear evidence for the enhancement of the conductance at the LaInO 3 /BaSnO 3 interface for a compensated BaSnO 3 :La channel layer. More importantly, we report on the length scale of the charge accumulation at the heterointerface and with that further support the finding of a 2DEG at the heterointerface. We also present the low temperature electrical properties of the heterointerface, displaying reduced carrier density and increased mobility Results and Discussion Structural Properties of the HeterostructureA high-resolution X-ray diffraction (HRXRD) 2θ−ω scan around the (220) NdScO 3 Bragg reflection shows three contributions, which can be attributed to the BaSnO 3 and SrSnO 3 films as well as to the NdScO 3 substrate (see Figure 1a). The SrSnO 3 film peak appears at 44.7°, which corresponds to a vertical lattice parameter of 4.056 Å. This coincides with the expected vertical lattice parameter of a fully compressively strained film, which is obtained from linear elasticity theory under the assumption of a Poisson ratio of ν = 0.23 and a lattice mismatch of 0.5% in [1-10] direction and 0.8% in [001] direction of the NdScO 3 substrate. [17] An reciprocal space mappings (RSM) measurement (Figure 1c) in the vicinity of the asymmetric (332) NdScO 3 substrate reflection exhibits the SrSnO 3 contribution directly belowThe properties of the conductance at the LaInO 3 /BaSnO 3 heterointerface are reported. The heterointerface is formed by covering the semi-insulating BaSnO 3 :La thin films with 10 nm LaInO 3 films, which are all epitaxially grown on NdScO 3 substrates. Structural properties of BaSnO 3 thin films are investigated by means of X-ray diffraction and transmission electron microscopy and exhibit a threading dislocation density of 6 × 10 10 cm −2 . Via capacitance-voltage (C-V) measurements, clear evidence is present for the accumulation of electrons at the interface within 2.5 nm in the BaSnO 3 layer, confirming the formation of a 2D electron gas (2DEG). Additionally, temperature dependent Hall effect measurem...

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Section: Introductionsupporting

confidence: 62%

“…depending on their chemical composition and crystal structure. [1][2][3][4][5] In addition, electrical properties of perovskites can easily be manipulated by doping and/or incorporation of lattice strain, which enables their use in various applications. [6,7] However, the main challenge has been their high carrier density and low mobility.…”

Section: Introductionmentioning

confidence: 99%

Confinement of Electrons at the LaInO₃/BaSnO₃ Heterointerface

Pfützenreuter

Kim

Cho

et al. 2022

Adv Materials Inter

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“…It is mainly because the distribution of X-ray diffraction intensity from a multi-domain crystal may be as complex as the domain patterns themselves. Up until now, single-crystal X-ray diffraction was successfully applied for characterization of domains in epitaxial thin films (Ehara et al, 2017;Braun et al, 2018;von Helden et al, 2018;Lee et al, 2019Lee et al, , 2020Schmidbauer et al, 2020) where possible domain patterns are greatly limited by the constraints imposed by the substrate.…”

Section: Introductionmentioning

confidence: 99%

Identification of a coherent twin relationship from high-resolution reciprocal-space maps

Gorfman¹,

Spirito²,

Zhang³

et al. 2022

Acta Cryst Sect A

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Twinning is a common crystallographic phenomenon which is related to the formation and coexistence of several orientation variants of the same crystal structure. It may occur during symmetry-lowering phase transitions or during the crystal growth itself. Once formed, twin domains play an important role in defining physical properties: for example, they underpin the giant piezoelectric effect in ferroelectrics, superelasticity in ferroelastics and the shape-memory effect in martensitic alloys. Regrettably, there is still a lack of experimental methods for the characterization of twin domain patterns. Here, a theoretical framework and algorithm are presented for the recognition of ferroelastic domains, as well as the identification of the coherent twin relationship using high-resolution reciprocal-space mapping of X-ray diffraction intensity around split Bragg peaks. Specifically, the geometrical theory of twinned ferroelastic crystals [Fousek & Janovec (1969). J. Appl. Phys. 40, 135–142] is adapted for the analysis of the X-ray diffraction patterns. The necessary equations are derived and an algorithm is outlined for the calculation of the separation between the Bragg peaks, diffracted from possible coherent twin domains, connected to one another via a mismatch-free interface. It is demonstrated that such separation is always perpendicular to the planar interface between mechanically matched domains. For illustration purposes, the analysis is presented of the separation between the peaks diffracted from tetragonal and rhombohedral domains in the high-resolution reciprocal-space maps of BaTiO3 and PbZr1−x Ti x O3 crystals. The demonstrated method can be used to analyse the response of multi-domain patterns to external perturbations such as electric field, change of temperature or pressure.

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“…The structural and compositional analysis reveals that the K 0.7 Na 0.3 NbO 3 films grow epitaxially in a perfect manner on TbScO 3 with the intended stoichiometric composition. 20 The surface of (110)-oriented TbScO 3 is defined by the lattice parameters 2 Â 3.960 Å and 2 Â 3.959 Å along the two in-plane orientations, [110] TSO and [001] TSO , 21 whereas the pseudocubic lattice parameters of bulk K 0.7 Na 0.3 NbO 3 using Vegard's law are a pc ¼ 3.954 Å and b pc ¼ c pc ¼ 4.014 Å with a monoclinic distortion angle a ¼ 89.7 between the b pc and c pc axes. [22][23][24] As a consequence of the epitaxy, the K 0.7 Na 0.3 NbO 3 film grows c pc -axis-oriented with a strongly compressed b pc axis and a slightly enlarged a pc axis.…”

mentioning

confidence: 99%

“…[22][23][24] As a consequence of the epitaxy, the K 0.7 Na 0.3 NbO 3 film grows c pc -axis-oriented with a strongly compressed b pc axis and a slightly enlarged a pc axis. Moreover, due to the highly regular formation of "superdomains" in the K 0.7 Na 0.3 NbO 3 film, 20 relaxation, the resulting effective in-plain strain in the K 0.7 Na 0.3 NbO 3 film is compressive and differs slightly (0.025%) for the [110] TSO and [001] TSO orientations. The observed domain structure and film symmetry are investigated in detail in Ref.…”

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confidence: 99%

Surface acoustic waves in strain-engineered K0.7Na0.3NbO3 thin films

Liang

Dai

Helden

et al. 2018

Applied Physics Letters

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Epitaxial K0.7Na0.3NbO3 thin films are grown via metal-organic chemical vapor deposition on (110)-oriented TbScO3. The films are strained due to the substrate–film lattice mismatch and therefore exhibit a strong and anisotropic modification of all its ferroelectric properties. The compressive in-plane strain leads to a reduction of the ferroelectric transition temperature from approximately 700 K for unstrained K0.7Na0.3NbO3 to 324 K and 330 K with maximum permittivities of 10 270 and 13 695 for the main crystallographic directions [001]TSO and [11¯0]TSO, respectively. Moreover, the quite thin films (approx. 30 nm thick) exhibit very large piezoelectric properties. For instance, surface acoustic waves with intensities of up to 4.7 dB are recorded for wave propagation along the [11¯0]TSO direction. The signal is smaller (up to 1.3 dB) along [001]TSO, whilst for the intermediate direction [11¯2]TSO, the signal seems to vanish (<0.1 dB). The results indicate that the choice of material, (K,Na)NbO3, in combination with strain-engineering via epitaxial growth onto lattice-mismatched substrates represents a promising way to optimize ferroelectric materials for piezoelectric thin-film applications.

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Ferroelectric monoclinic phases in strained K_0.70Na_0.30NbO₃ thin films promoting selective surface acoustic wave propagation

Cited by 19 publications

References 82 publications

Confinement of Electrons at the LaInO₃/BaSnO₃ Heterointerface

Confinement of Electrons at the LaInO₃/BaSnO₃ Heterointerface

Identification of a coherent twin relationship from high-resolution reciprocal-space maps

Surface acoustic waves in strain-engineered K0.7Na0.3NbO3 thin films

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Ferroelectric monoclinic phases in strained K0.70Na0.30NbO3 thin films promoting selective surface acoustic wave propagation

Cited by 19 publications

References 82 publications

Confinement of Electrons at the LaInO3/BaSnO3 Heterointerface

Confinement of Electrons at the LaInO3/BaSnO3 Heterointerface

Identification of a coherent twin relationship from high-resolution reciprocal-space maps

Surface acoustic waves in strain-engineered K0.7Na0.3NbO3 thin films

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Product

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Ferroelectric monoclinic phases in strained K_0.70Na_0.30NbO₃ thin films promoting selective surface acoustic wave propagation

Confinement of Electrons at the LaInO₃/BaSnO₃ Heterointerface

Confinement of Electrons at the LaInO₃/BaSnO₃ Heterointerface