Epitaxial BaTiO3 Thin Films Research Articles

Epitaxial BaTiO3 Thin Films on Different Substrates for Optical Waveguide Applications

AbstractIn the process of developing thin film electro-optical waveguides we investigated the influence of different substrates on the optical and structural properties of epitaxial BaTiO3 thin films. These films are grown by on-axis pulsed laser deposition (PLD) on MgO(100), MgAl2O4(100), SrTiO3(100) and MgO buffered A12O3(1102) substrates. The waveguide losses and the refractive indices were measured with a prism coupling setup. The optical data are correlated to the results of Rutherford backscattering spectrometry/ion channeling (RBS/C). X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). BaTiO3 films on MgO(100) substrates show planar waveguide losses of 3 dB/cm and ridge waveguide losses of 5 dB/cm at a wavelength of 633 nm.

Dielectric properties of epitaxial BaTiO3 thin films

The dielectric response of epitaxial BaTiO3 thin films deposited on MgO was measured through surface electrodes as a function of applied bias, frequency, and temperature. The room temperature value of the dielectric constant was ∼500 with a dissipation factor, tan(δ), of 0.05 at 100 kHz. Measurements varying the bias field showed hysteresis of the dielectric response and a tunability of 30% for a maximum applied field of ∼7 MV/m. The frequency response of the dielectric constant is well described by a Curie–von Schweidler power law with an exponent ∼0.04 in the range 1 kHz–13 MHz. The films undergo a diffuse phase transition at temperatures higher than the bulk Curie temperature. The behavior of the dielectric response is attributed to the presence of residual strain in the epitaxial thin films.

Luminescence quenching in Er-doped BaTiO3 thin films

Luminescence quenching in Er-doped epitaxial BaTiO3 thin films was investigated. From transient photoluminescence, nonradiative decay processes were measured, and a nonradiative resonant energy transfer model was developed. The nonradiative transition rate is linearly proportional to the OH impurity concentration in the films, indicating it is responsible for the observed quenching behavior.

Structural and optical characterization of epitaxial waveguiding BaTiO3 thin films on MgO

Epitaxial waveguide structures of c-axis oriented BaTiO3 thin films on MgO(001) have been grown by pulsed laser deposition. The structural properties of the samples have been characterized by Rutherford backscattering spectrometry/ion channeling (RBS/C), x-ray diffraction, and atomic force microscopy. We found excellent crystalline quality even up to thicknesses of a few microns. This has been confirmed by RBS/C minimum yield values of 2%–3%, a full width at half maximum of 0.36° of the BaTiO3 (002) rocking curve, and a rms roughness of 1.1 nm for a 950 nm BaTiO3 film. The out-of-plane refractive index was measured to be close to the extraordinary bulk value with the birefringence being about one third of the bulk value. Waveguide losses of 2.9 dB/cm have been demonstrated.

Microstructural development of BaTiO3 heteroepitaxial thin films by hydrothermal synthesis

The hydrothermal growth of epitaxial BaTiO3 thin films on single-crystal SrTiO3 substrates occurs by the island growth mode. The aqueous solution chemistry is found to control interfacial characteristics and plays an important role in controlling film formation and faceting. Island faceting can be changed by the introduction of additional cations during synthesis. Electrophoretic data, confirmed by adsorption measurements, show that barium is a potential determining counterion and adsorbs on SrTiO3 surfaces. Initial electrical measurements show that the BaTiO3 films have a dielectric constant of 141 with a loss tangent of 0.9 that decreases with heat treatment.

Strain in Epitaxial BaTiO3 Thin Films Prepared by MOCVD

AbstractThe microstrain in epitaxial BaTiO3 thin films has been investigated using x-ray diffraction. The full width half maximum of the (001) diffraction peaks ranged from 0.12 to 0.49 deg. From the analysis of the angular dependence of the diffraction peak broadening, it is concluded that the broadening is due predominantly to strain. The magnitude of the microstrain decreases sharply with increasing film thickness.

Ferroelectric domains in epitaxial PbTiO3 and BaTiO3 thin films on MgO(100)

Epitaxial PbTiO3 and BaTiO3 thin films were prepared on MgO(100) by laser ablation and RF magnetron sputter deposition, respectively. X-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM) were used to investigate the ferroelectric domains in the grown films. In the PbTiO3 film, significant portions of a-domains were distributed in c-domains, which causes abundant 90° domain population. On the other hand, the BaTiO3 film was mainly single c-domains without any meaningful domain structure. We attribute the difference in domain population of the two reasons. One is the smaller phase transformation strain which comes from smaller tetragonality of BaTiO3, and the other is the larger compressive stress due to thermal mismatch which comes from lower Tc of BaTiO3 than those of PbTiO3.

Hydrogen complexes in epitaxial BaTiO3 thin films

Hydrogen complexes in epitaxial BaTiO3 thin films are investigated using Fourier transform infrared spectroscopy. Both undoped and Er-doped layers were grown using low-pressure metal–organic chemical vapor deposition. From the infrared spectra of the undoped and Er-doped films grown at 750–800 °C, infrared absorption was observed at 3486 cm−1. The absorption peak is attributed to a vibrational mode of O–H in BaTiO3. Moreover, the Er-doped layers showed additional absorption peaks at 2905 and 2964 cm−1. The peaks are ascribed to the vibrational modes of C–H complexes in the Er-doped layers.

Preparation of Epitaxial BaTiO3 Thin Films by the Dipping-pyrolysis Process

Epitaxial BaTiO3 thin films were prepared on SrTiO3 (100) substrates by the dipping-pyrolysis process using metal naphthenates as starting materials. Highly oriented BaTiO3 thin films were crystallized by heat treatment at 800 °C and higher, from amorphous precursor films pyrolyzed at 470 °C. XRD pole-figure and reciprocal-space mapping analyses showed that the films were epitaxially grown on SrTiO3substrates and were pseudocubic phase with an a║/aτ ratio of 1.003, smaller than the c0/a0 ratio (=1.011) of bulk tetragonal BaTiO3.

Defect Generation And Evolution In The Hydrothermal Growth Of Epitaxial BaTiO3Thin Films

ABSTRACTThe structure of epitaxial BaTiO3thin films prepared by hydrothermal synthesis on (001) SrTiO3substrates was studied by transmission electron microscopy (TEM). The growth evolution was followed from initial island formation, through island impingement and fusion. Plan view and cross-section imaging demonstrated that the films grew by an unusual islanding mechanism. Electron diffraction showed the islands and the fully formed film are single crystal with mosaic character and in all cases strain relaxed. Cross-section TEM of the early growth films showed a several monolayer thick interfacial layer and the film/substrate region had no misfit dislocations. In the fully formed films, this interfacial layer was not observed, however a clear misfit dislocation network was observed. Defects analysis shows that the misfit dislocations have pure edge character with <100> Une directions, and <010> Burgers vectors (parallel to the film/substrate interface).

Pinning of 90° domain boundaries at interface dislocations in BaTiO3/LaAIO3 {100}

Epitaxially grown BaTiO3 thin films have potential applications in microelectronics and integrated photonics. The ferroelectric property of this material is largely determined by the domain structure. It is believed that the structure of the substrate would have profound effect on the quality of BaTiO3 epitaxial thin films. This paper reports our studies on the pinning of 90° domain boundaries at interface dislocations.Epitaxial BaTiO3 thin films were deposited on single crystalline LaAIO3 (100) substrates at 800°C by metal-organic chemical vapor deposition (MOCVD). Cross-section specimens of the films were studied at 200 kV using an JEOL 2010 high-resolution transmission electron microscope (HRTEM).

Electrical transport properties of epitaxial BaTiO3 thin films

Measurements of the temperature dependent transport properties of epitaxial BaTiO3 are reported. Electrical resistivity and thermoelectric power were measured over the temperature range of 77–300 K. Room temperature resistivities of the as-deposited, undoped films range from 105 to 108 Ω cm, while values as low as 55 Ω cm are obtained for the La-doped films. The resistivity shows an activated temperature dependence with the measured activation energies ranging between 0.11 and 0.50 eV. The activation energy depends strongly upon the thin film carrier concentration. Thermoelectric power measurements indicate that the films are n-type. The Seebeck coefficient for La-doped BaTiO3 exhibits metallike behavior, with its magnitude directly proportional to temperature. Temperature dependent resistivity and thermopower measurements indicate that the carrier mobility is activated. A transport model is proposed whereby conduction occurs in the La-doped films via hopping between localized states within a pseudogap formed between a lower Hubbard band and the BaTiO3 conduction band edge.

Preparation of Semiconductive Epitaxial BaTiO<sub>3</sub> Thin Film and its Electrical Properties

Submicron semiconductive epitaxial BaTiO3 thin film was prepared on (100) MgO substrate. An epitaxially grown BaTiO3 film prepared by MOCVD was coated with ethanol solution of LaCl3 and heated under a reducing atmosphere at 800-1200°C. The resistivity was less than 1Ω·cm and the carrier concentration was in the order of 1018cm-3. The film was n-type semiconductor and the resistivity increased abruptly with the increase in temperature above 600°C in air because of the decrease of the carrier concentration.

Structural characterization of epitaxial BaTiO3 thin films grown by sputter deposition on MgO(100)

Epitaxial thin films of BaTiO3 have been prepared using radio-frequency magnetron sputter deposition on MgO(100) substrates. Various x-ray-diffraction techniques were employed to characterize the crystal structure of the films. The films were fully tetragonal and consisted of c domains. Their tetragonality has been shown to be 1.013, which is almost the same as the bulk value of BaTiO3. However, the cross-sectional transmission electron microscopic micrograph showed that a very small amount of a domains coexists forming 90° domain boundaries in the matrix of c domains. In spite of the negligible strain caused by the phase transformation, it seems to be inevitable to form a certain small amount of a domains in the BaTiO3 film on MgO system.

Growth of Epitaxial BaTiO3 Thin Films at 600°C by Metalorganic Chemical Vapor Deposition

ABSTRACTMetalorganic chemical vapor deposition (MOCVD) was used to deposit epitaxial BaTiO3 thin films on (100) MgO substrates at 600°C. The metalorganic precursors employed in the deposition experiments were hydrated Ba(thd)2 (thd = C11H19O2) and titanium isopropoxide. The films were analyzed by means of transmittance spectroscopy, wavelength dispersive x-ray spectrometry, secondary ion mass spectrometry depth profiling, x-ray diffraction, high resolution transmission electron microscopy, selected area electron diffraction, nanoscale energy dispersive x-ray spectrometry and second harmonic generation measurements. There was no evidence for interdiffusion between the film and substrate. The x-ray and electron diffraction studies showed that the films were oriented with the a-axis normal to the substrate surface, whereas second harmonic generation measurements showed that the films had some c-axis character.

Epitaxial Growth of Pt(001) Thin Films on MgO(001) Under Oxidizing Conditions

AbstractEpitaxial Pt(001) thin films have been grown on MgO(001) substrates using dc magnetron sputtering with an Ar/O2 mixture at 700°C. The width (FWHM) of the rocking curve of the Pt(002) peak is between 0.16° and 0.20°, which is only 0.05° wider than that of the MgO (002) peak of the cleaved substrate. The film surface roughness is about 1 nm (rms) for a 240 nm thick Pt film. No grain structure could be observed using SEM. In contrast, the films deposited at 700 °C with pure Ar, have both Pt(111) and Pt(001) oriented growth, as shown by XRD Θ - 2 Θ scans, with the Pt(111) peak having the largest intensity. BaTiO3 epitaxial films have also been deposited on Pt(001)/MgO(001). The width (FWHM) of the rocking curve of the BaTiO3(200) peak is 0.4°. The surface morphology of the epitaxial BaTiO3(100) thin films on Pt(001)/MgO(001) is featureless. XRD pole figure measurements on Pt/BaTiO3/Pt trilayer shown a very good in-plane alignment of all layers. The epitaxial growth relationship was also confirmed by TEM electron diffraction and cross-section imaging. The Pt/BaTiO3/Pt epitaxial trilayer could serve as a prototype for ferroelectric capacitors and may be able to improve the electrical properties of the capacitors.

Epitaxial growth of MgO on GaAs(001) for growing epitaxial BaTiO3 thin films by pulsed laser deposition

MgO buffer layers were deposited on GaAs by pulsed laser deposition for epitaxial growth of BaTiO3. MgO was grown epitaxially on GaAs for the first time; the orientation is (001) on GaAs(001). The best crystallographic quality was obtained at 350 °C in 5×10−6 Torr O2. BaTiO3 films with (001) orientation grew epitaxially on MgO/GaAs. The in-plane epitaxial relationship was BaTiO3[100]∥ MgO[100]∥ GaAs[100] in spite of a large lattice mismatch (25.5%) between MgO and GaAs.

Epitaxial growth of BaTiO3 thin films by organometallic chemical vapor deposition

Epitaxial BaTiO3 thin films were grown in situ on (100) LaAlO3 by low-pressure organometallic chemical vapor deposition using the precursors Ba (hexafluoroacetylacetonate)2 (tetraglyme) and titanium tetraisopropoxide. The phase composition and epitaxial quality were sensitive to the reactant partial pressures and growth temperature. Deposition at 800 °C yielded [100]-oriented BaTiO3 films. In-plane epitaxy was confirmed for the BaTiO3 films by x-ray diffraction.