Transferable highly (001)-oriented textured ferroelectric BaTiO3 thin films have been achieved on a graphene monolayer for wearable devices like sensors and actuators for future “Internet of Things” era.
In this work, we demonstrate the electronic tunability of surface acoustic waves (SAWs) in epitaxially strained relaxor-type ferroelectric thin films. Epitaxial K0.7Na0.3NbO3 thin films of typically 30 nm in thickness are grown via pulsed laser deposition on (110)-oriented TbScO3. A partial plastic lattice relaxation of the epitaxial strain in these samples leads to a relaxor-type ferroelectricity of these films, which strongly affects the SAW properties. Without electronic bias, only tiny SAW signals of ∼0.2 dB can be detected at room temperature, which can be boosted up to ∼4 dB by a static voltage bias added to the high frequency driving current of the SAW transducers. Upon field cooling below the freezing temperature of polar nanoregions (PNRs), this strong SAW signal can be preserved and is even enhanced due to a release of the electronically fixed PNRs if the bias is removed. In contrast, at elevated temperatures, a reversible switching of the SAW signal is possible. The switching shows relaxation dynamics that are typical for relaxor ferroelectrics. The relaxation time τ decreases exponentially from several hours at freezing temperature to a few seconds (<5 s) at room temperature.
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...
The use of LaInO3 with (110) surface orientation was investigated as a novel orthorhombic substrate for the epitaxial growth of semiconducting BaSnO3 thin films. On the basis of reflection high-energy electron diffraction, energy dispersive x-ray analysis and inductively coupled plasma-optical emission spectrometry measurements, we revealed that slight Ba doping of LaInO3 crystals is beneficial to stabilize the substrate surface, which facilitates the epitaxial growth of well-ordered BaSnO3 thin films by pulsed laser deposition. Fully strained BaSnO3 films without misfit dislocations found by means of transmission electron microscopy were achieved due to the negligible lattice mismatch between BaSnO3 film and Ba-doped LaInO3 substrate. Electric properties of La-doped BaSnO3 films exhibit a Hall-mobility of 69 cm2 V−1 s−1 at room temperature and 99 cm2 V−1 s−1 at 20 K at a constant charge carrier density of 3.8·1019 cm−3.
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