Growth Of SrTiO3 Films Research Articles

SrTiO<sub>3</sub> Thin Films Deposition Using Pulsed Laser Deposition Technique

Strontium titanate (SrTiO3) thin film has been deposited on Si (100) substrate using pulsed laser deposition technique. Film deposition was carried out at low temperature (150°C) by maintained the pressure at 10-4 Torr. Nanometer-thick SrTiO3 film on Si substrate was characterized using SEM, AFM, XRD, and Raman Spectroscopy. SEM and AFM images show that SrTiO3 film has growth on Si substrate uniformly. Raman and XRD spectroscopy also support the growth of SrTiO3 film on Si substrate. Furthermore, to investigate the effect of post-deposition thermal annealing, the samples were annealed up to 900°C. Thermal stability of SrTiO3/Si structure was studied by mean XRD spectra. The X-Ray Diffraction pattern indicates the crystallinity improvement through atomic arrangements during thermal annealing process.

Kinetics of formation and growth of epitaxial SrTiO3 films of single-crystal (001) SrTiO3 supports

The aim of this study was to quantitatively estimate the kinetics of the formation and growth of oxide SrTiO3 (STO) films using the method of the in situ reflection high-energy electron diffraction (RHEED) and compare the obtained results with the known growth models and theoretical estimates. The kinetics of the relaxation and crystallization of particles is studied under pulsed laser deposition (PLD) from oxide targets onto (001) STO supports or onto the surface of STO film growth at 650–800°C. Deposition frequencies of 0.1–10 Hz typical of PLD were used. The surface morphology and film structure was studied ex situ using the methods of AFM and X-ray-structural analysis. It was found that the time of relaxation of deposited particles is within the range of 2–20 s, which greatly exceeds or is comparable to the relative pulse duration. It was experimentally shown that structural distortions in epitaxial films for temperatures of ≤900°C are mainly due to the high rate of deposition and limited surface mobility of particles. The effect of structural relaxation in films is observed after the end of deposition; the time constant of bulk structural relaxation is ∼10 − ∼102 s or more. The obtained kinetic parameters of the formation of an oxide structure may be useful for the development of crystallization theory, as well as to optimize the conditions of epitaxial oxide film growth.

In-situ monitoring of EuTiO3 and SrTiO3 film growth using time-resolved X-ray scattering during pulsed-laser deposition

Time-resolved X-ray scattering was employed to in-situ monitor the epitaxial growth process of the thin films and multilayers of EuTiO3 and SrTiO3 during pulsed laser deposition. The temporal intensity oscillations of the reflected X-rays at anti-Bragg position and the transient processes following the flux pulses were observed. The temporal intensity oscillations were used to control the film thickness, and the reflectivity along the crystal truncation rod was used to measure both the film thickness and the surface/interface roughness. The primary features of the X-ray intensity oscillations were reproduced via simulating the experimental data using diffusive rate equation model. Several mechanisms of determining the X-ray intensity features were discerned.

An annealing study of an oxygen vacancy related defect in SrTiO3 substrates

The study addresses the stability of point defects in SrTiO3 (STO) during thin film processing using electron paramagnetic resonance (EPR) spectroscopy. In particular, the intensity of the Fe3+VO EPR signal is monitored after various steps during the growth of STO films on STO substrates. Controlled O2 and vacuum heat treatments are also performed to clarify the fundamental mechanisms responsible for the effects of different processing steps. Comparison of results from film fabrication with those obtained during exposure to the control ambient shows that the presence of oxygen in the pretreatment growth atmosphere decreases the amount of the Fe3+VO complex, but exposure to the low pressure environment of the growth chamber returns the signal to the original intensity. These results are consistent with accepted theories of oxygen vacancy diffusion. However, an unexpected decrease in the oxygen vacancy related signal is also observed during vacuum treatment of an as-received sample. Furthermore, the decrease occurs over the same temperature range as seen for an O2 anneal. The difference between the O2 and vacuum treatments is revealed in postannealing photoinduced EPR and resistivity measurements, which indicate that vacancy related centers change charge state during the O2 anneal and are not removed by oxygen. The effect of the vacuum treatment, though different from that of oxygen, is not yet clear as no charge state changes were induced after exposure to visible or ultraviolet radiation, but the conductivity of the samples changed.

Sulfide and Oxide Heterostructures For the SrTiO3 Thin Film Growth on Si and Their Structural and Interfacial Stabilities

Epitaxial SrTiO3 (STO) thin films with high electrical properties were grown on Si using ZnS single- and SrS/MnS hetero-buffer layers. STO films on both ZnS-buffered and SrS/MnS-buffered Si showed two growth orientations, (100) and (110). The temperature dependence of the growth orientation for STO films was different for the ZnS single-buffer layer in comparison with the SrS/MnS heterobuffer layers. (100) growth of STO films on SrS/MnS-buffered Si became dominant at high temperatures about 700 °C, while (100) growth of STO films on ZnS-buffered Si became dominant at a relatively low growth temperature of 550 °C. STO(100) films on ZnS-buffered and SrS/MnS-buffered Si showed lattice and domain matches for epitaxial relationships with [001]ZnS∥[011]STO and SrS[001]∥[011]STO, respectively via 45° in-plane rotation of STO films relative to both ZnS and SrS layers. The ZnS buffer layer contained many stacking faults because of the mismatch between ZnS and Si, however, those defects were terminated at the ZnS/STO interface. In contrast, the MnS buffer was very stable against stacking defect formation. Transmission electron microscopy measurements revealed the presence of a disordered region at the ZnS/Si and MnS/Si interfaces. Auger electron spectroscopy and transmission electron microscopy results showed that a good MnS/Si interface at the initial growth stage degraded to a SiS2-x-rich phase during MnS deposition and again into a SiO2-x-rich phase during STO deposition at the high growth temperature of 700 °C. It was also observed that STO on SrS/MnS-buffered Si showed a markedly high dielectric constant compared with that of STO on ZnS-buffered Si.

Two-step growth of SrTiO3 films on Sr-modulated Si(001) substrates

Perovskite-type SrTiO3 (STO) films have been grown on the Sr-modulated Si(001) substrates using “two-step growth method” with a molecular beam epitaxy technique. About 6 A Sr was deposited on the surface of chemically formed SiO2/Si at 800 ∘C, which resulted in the formation of Si(001)-Sr(2 × 1) surface. About 250-A-thick STO films have been deposited on the Si(001)-Sr(2 × 1) surface at 350 ∘C in the O2 partial pressure of approximately 3 × 10−7 Torr (first step), followed by an annealing at 600 ∘C in a pressure of 3 × 10−9 Torr (second step). Reflection high-energy electron diffraction patterns of grown films become elongated streaky features after the annealing, suggesting the solid-phase epitaxial growth of STO. The presence of strong STO(001) and STO(002) diffraction peaks in X-ray diffraction measurements suggests that the high-quality crystalline STO films grow on the Sr-modulated Si(001) substrates by the two-step growth method. Atomic force microscopy image shows the smooth surface with root mean square roughness of about 18 A.

Roles of the first atomic layers in growth of SrTiO3 films on LaAlO3 substrates

Growth behaviors of SrTiO3/LaAlO3 films could be varied substantially by controlling terminating atomic layers of the substrates. In a film on the LaO-terminated substrate, strain-induced roughening was observed. In a film on the AlO2-terminated substrate, the first atomic layer of the interface seemed to have lots of defects. However, the stress became quickly relaxed, so a SrTiO3 film could be grown in a layer-by-layer mode after a few monolayers. All these observations could be explained in terms of chemical matching between the atomic layers at the interface.

MOCVD Growth of Epitaxial SrTiO3 Thin Films on YBa2 Cu3O7−x/LaAlO3

AbstractStrontium titanate (SrTiO3) thin films have been epitaxially grown on YB2Cu3O7−x (YBCO)/LaAlO3 at substrate temperatures of 660 to 700°C. X-ray diffraction (XRD) results indicated that single crystalline SrTiO3 thin films were epitaxially grown on the substrate with <100> orientation perpendicular to the substrates. The compositions of the films with different growth conditions were examined by Rutherford backscattering spectroscopy (RBS) and energy dispersive x-ray spectroscopy (EDX). The ratio of Sr/Ti is in the range of 0.9 to 1.1 for the films with a thickness of 1000–2000Å. The surface morphology of the films and the interfaces of the SrTiO3/YBCO structure were examined by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Very smooth surface and sharp interface were observed. The superconducting property of the YBCO layer, as measured by ac susceptibility, did not degrade after growth of SrTiO3 film. The dielectric constant as high as 320 was obtained at 100KHz. The leakage current density is less than 1×10−6A/cm2 at 3V operation.

Oriented Growth of SrTiO3 Films on Si(100) Substrates Using In—situ Cleaning By Excited Hydrogen

AbstractIn—situ cleaning of Si surfaces in vacuum was successfully performed using excited hydrogen and it was applied to epitaxial growth of SrTiO3 films on Si(100) substrates. Epitaxial growth of SrTiO3 films was observed under optimum cleaning conditions, however, the epitaxial nature was found to be destroyed for films thicker than 50 nm, which is probably due to the non—stoichiometry of the films. The electrical properties of the initially epitaxial SrTiO3 films grown on the cleaned Si substrates were better than those of polycrystalline ones.