G. R. Bai

Single-crystal Pb(ZrxTi1−x)O3 thin films prepared by metal-organic chemical vapor deposition: Systematic compositional variation of electronic and optical properties

Single-crystal thin films of Pb(ZrxTi1−x)O3 (PZT) covering the full compositional range (0⩽x⩽1) were deposited by metal-organic chemical vapor deposition. Epitaxial SrRuO3(001) thin films grown on SrTiO3(001) substrates by rf-magnetron sputter deposition served as template electrode layers to promote the epitaxial growth of PZT. X-ray diffraction, energy-dispersive x-ray spectroscopy, atomic force microscopy, transmission electron microscopy, and optical waveguiding were used to characterize the crystalline structure, composition, surface morphology, microstructure, refractive index, and film thickness of the deposited films. The PZT films were single crystalline for all compositions exhibiting cube-on-cube growth epitaxy with the substrate and showed very high degrees of crystallinity and orientation. The films exhibited typical root mean square surface roughness of ∼1.0–2.5 nm. For tetragonal films, the surface morphology was dominated by grain tilting resulting from ferroelectric domain formation. We r...

Substrate effects on the structure of epitaxial PbTiO3 thin films prepared on MgO, LaAlO3, and SrTiO3 by metalorganic chemical‐vapor deposition

Epitaxial PbTiO3 films were prepared by metalorganic chemical‐vapor deposition on MgO(001)‐, SrTiO3(001)‐, and LaAlO3(001)‐oriented substrates. Four‐circle x‐ray diffraction, transmission electron microscopy, Rutherford backscattering (RBS) channeling, and optical waveguiding were performed to characterize the deposited films. Epitaxial, single‐crystal films were obtained on all three substrate materials under the same growth conditions. However, the defect structure of the films, including grain tilting, threading dislocation density, and 90° domain formation, was strongly dependent on the choice of substrate material. Films grown on MgO(001) and LaAlO3(001) (pseudocubic indices) substrates are nominally c‐axis oriented; however, the PbTiO3 grains in the film form a fourfold domain structure, with the grains tilted ∼0.6° and ∼0.7°, respectively, toward the [100] directions (cubic or pseudo‐cubic) of the substrates. In addition, these films contain a significant volume fraction of 90°‐domain (a‐axis) stru...

Low-temperature growth and orientational control in RuO2 thin films by metal-organic chemical vapor deposition

For growth temperatures in the range of 275°C to 425°C, highly conductive RuO2 thin films with either (110)- or (101)-textured orientations have been grown by metal-organic chemical vapor deposition (MOCVD) on both SiO2/Si(001) and Pt/Ti/SiO2/Si(001) substrates. Both the growth temperature and growth rate were used to control the type and degree of orientational texture of the RuO2 films. In the upper part of this growth temperature range (∼ 350°C) and at a low growth rate ( 3.0 nm/min.), the RuO2 films favored a (101)-textured orientation. In contrast, higher growth temperatures (> 425°C) always produced randomly-oriented polycrystalline films. For either of these low-temperature growth processes, the films produced were crack-free, well-adhered to the substrates, and had smooth, specular surfaces. Atomic force microscopy showed that the films had a dense microstructure with an average grain size of 50–80 nm and a rms. surface roughness of ∼ 3–10 nm. Four-probe electrical transport measurements showed that the films were highly conductive with resistivities of 34–40 μΩ-cm (at 25°C).

The relationship between the MOCVD parameters and the crystallinity, epitaxy, and domain structure of PbTiO 3 films

Lead- and titanium-based oxide thin films were prepared by the metal-organic chemical vapor deposition technique (MOCVD) and the relationship between the film structures and the processing parameters, such as the ratio of Pb/Ti precursors in the gas phase, substrate materials, substrate surface orientation, and growth temperature, was systematically studied. It was found that whether a single-phase stoichiometric PbTiO[sub 3] film could be obtained depended on both the Pb/Ti precursor ratio in the gas phase and the deposition temperature. Under appropriate conditions, stoichiometric PbTiO[sub 3] films could be obtained on all the substrates including silicon, MgO, [alpha]--Al[sub 2]O[sub 3], SrTiO[sub 3], and LaAlO[sub 3]. The PbTiO[sub 3] films grown on silicon substrates were always polycrystalline, whereas epitaxial PbTiO[sub 3] films were obtainable on all the other substrates. For epitaxial PbTiO[sub 3] films, the epitaxial relationship, crystallinity, and domain structures were found to be a function of both the substrate materials and surface orientation as well as the deposition temperature. X-ray rocking curves ([omega] scan) of the (100) and (001) planes of PbTiO[sub 3] epitaxial films and PbTiO[sub 3] single crystal revealed the inherent nature of the domain structures in PbTiO[sub 3].

GROWTH OF HIGH QUALITY SINGLE-DOMAIN SINGLE-CRYSTAL FILMS OF PBTIO3

Single‐crystal films of PbTiO3 have been deposited on (100) SrTiO3 substrates by metalorganic chemical vapor deposition. X‐ray diffraction spectra and transmission electron microscopy images revealed that the development of 90° domains was directly related to the thickness of the film. Single‐domain, single‐crystal films were obtained for film thickness less than 150 nm. The minimum yields of the films in ion‐channeling experiments were only 3 %, similar to that of a perfect single crystal. The ordinary refractive index of the film measured by optical waveguiding experiment was also the same as that of PbTiO3 single crystals.

Preparation of YVO4 thin films by metal organic chemical vapor deposition

YVO4 films were reproducibly prepared on (0001) and (11{bar 2}0) sapphire ({alpha}-Al{sub 2}O{sub 3}) substrates using metal organic chemical vapor deposition. X-Ray diffraction, transmission electron microscopy and X-ray energy dispersive spectroscopy were used to characterize the deposited films. It was found that under most growth conditions the films deposited on (0001) sapphire consisted of two layers, i.e. a stoichiometric bottom layer of YVO{sub 4} which was epitaxially grown on the substrate and a polycrystalline top layer of Y{sub 8}V{sub 2}O{sub 17}. The effect of growth parameters, in particular the growth temperature, on the stability of the dual layer structured films was studied and a working model explaining the origin of dual layer structure was suggested. Based on these observations the method for the preparation of stoichiometric epitaxial one layer-structured YVO{sub 4} films with either an in-plane variant or a single crystal structure on (0001) and (11{bar 2}0) sapphire ({alpha}-Al{sub 2}O{sub 3}) substrates, respectively, was presented.

Preparation and structure of PbZrO3 epitaxial films by metalorganic chemical vapor deposition

Single‐crystal PbZrO3 thin films have been grown on (001) SrTiO3 substrates by metalorganic chemical vapor deposition. The single‐crystal nature of c‐axis oriented PbZrO3 film is confirmed by x‐ray diffraction, selective area electron diffraction, and transmission electron microscopy. The epitaxial relationship between the PbZrO3 film and the SrTiO3 substrate was found to be (001)[100]PbZrO3∥(001)[110]SrTiO3.

Epitaxial Pb(Mg1/3Nb2/3)O3 thin films synthesized by metal-organic chemical vapor deposition

Metal-organic chemical vapor deposition was used to prepare Pb(Mg1/3Nb2/3)O3 (PMN) thin films on (001) SrTiO3 and SrRuO3/SrTiO3 substrates, using solid Mg β-diketonate as the Mg precursor. Parameters including the precursor ratio in the vapor phase, growth temperature, growth rate, and reaction pressure in the reactor chamber were varied in order to determine suitable growth conditions for producing phase-pure, epitaxial PMN films. A cube-on-cube orientation relationship between the thin film and the SrTiO3 substrate was found, with a (001) rocking curve width of 0.1°, and in-plane rocking-curve width of 0.8°. The root-mean-square surface roughness of a 200-nm-thick film on SrTiO3 was 2 to 3 nm as measured by scanning probe microscopy. The zero-bias dielectric constant and loss measured at room temperature and 10 kHz for a 200-nm-thick film on SrRuO3/SrTiO3 were approximately 1100 and 2%, respectively. The remnant polarization for this film was 16 μC/cm2.

Epitaxy‐induced phase of near‐stoichiometry PbTiO3 films prepared by metalorganic chemical vapor deposition

Ferroelectric PbTiO3 thin films have been prepared by a low‐pressure MOCVD process. Epitaxial films with a crystal structure of a bulk equilibrium tetragonal phase were readily obtained within a range of growth conditions. However, by providing excess Pb in the growth process, we have observed an epitaxy‐induced phase for near‐stoichiometry PbTiO3 which possesses a perovskite‐like, but possible, orthorhombic structure.Ferroelectric PbTiO3 thin films have been prepared by a low‐pressure MOCVD process. Epitaxial films with a crystal structure of a bulk equilibrium tetragonal phase were readily obtained within a range of growth conditions. However, by providing excess Pb in the growth process, we have observed an epitaxy‐induced phase for near‐stoichiometry PbTiO3 which possesses a perovskite‐like, but possible, orthorhombic structure.

In situ x-ray scattering study of PbTiO3 chemical-vapor deposition

We present in situ surface x-ray scattering measurements of PbTiO3 epitaxy by metal–organic chemical-vapor deposition. Oscillations in crystal truncation rod intensity corresponding to layer-by-layer growth are observed under a variety of growth conditions. At lower PbO overpressures, we observe a transition to step-flow growth and an increased rate of recovery after growth, indicating a higher surface mobility.