Growth Oxygen Pressure Research Articles

Critical examination of growth rate for magnesium oxide (MgO) thin films deposited by molecular beam epitaxy with a molecular oxygen flux

The authors report a study of molecular beam deposition of MgO films on amorphous SiO2 and (0001) GaN surfaces over a large range of temperatures (25–400 °C) and molecular oxygen growth pressures (10−7–10−4 Torr). This study provides insight into the growth behavior of an oxide with volatile metal constituents. Unlike other materials containing volatile constituents (e.g., GaAs, PbTiO3), all components of MgO become volatile at normal epitaxial growth temperatures (≥250 °C). Consequently, defining which species is the adsorption controller becomes ambiguous. Different growth regimes are delineated by the critical substrate temperature for Mg re-evaporation and the Mg:O flux ratio. These regimes have impact on phase purity, quartz crystal microbalance calibration, and film microstructure. The universal decay in deposition rate above growth 10−5 Torr O2 is also considered. By introducing a third flux of inert argon gas, rate reduction is attributed to increased molecular scattering and not oxidation of the metal source.

Influence of oxygen growth pressure on laser ablated Cr-doped In 2O 3 thin films

We present a systematic investigation of the effects of oxygen growth pressure on the structural, optical, and electrical properties of In 2O 3:Cr thin films grown by pulsed laser deposition. X-ray diffraction analysis showed increases in lattice constant from 10.103 Å to 10.337 Å, and in particle size from 13.9 nm to 35.5 nm as the oxygen growth pressure increased from 7.5 × 10 −6 Torr to 7.5 × 10 −3 Torr, respectively. The observed shift in the X-ray diffraction peaks to lower angles was assumed to be caused by the reduction in the lattice defect density, precisely oxygen vacancies. The optical transparency increased with partial oxygen pressure ( P O 2 ) , and an average transmittance of ∼85% was obtained at 7.5 × 10 −3 Torr. The films are highly conducting with resistivity as low as 2 × 10 −4 Ω cm and mobility as high as 133 cm/V s. Temperature dependent resistivity measurements in the 45 < T < 300 K temperature range reveal that films grown at 7.5 × 10 − 6 ≤ P O 2 ≤ 7.5 × 10 − 4 Torr exhibit negative temperature coefficient of resistivity (TCR) below approximately T = 60 K, T = 120 K, T = 160 K; then positive TCR in the temperature intervals 60 < T < 300 K, 120 < T < 300 K, and 160 < T < 300 K, respectively. This suggests that two disparate mechanisms govern electrical dc transport in the two temperature regions. Film grown at P O 2 of 7.5 × 10 −3 Torr displayed typical semiconducting behavior with negative TCR in the whole temperature region.

PLD법에 의한 Mg가 첨가된 CuCrO2박막 성장

We report on the growth of films using pulsed laser deposition and their structural and electrical transport properties. thin films were doped with 5 at% Mg for p-type properties. Epitaxial films of were grown on c-plane sapphire substrates. The effects of growth temperature and oxygen pressure on film properties were investigated. The main phase of delafossite was appeared above the growth temperature of . The thin film grown at showed the highest conductivity, reaching 19.6 S/cm while higher growth temperatures over led to lower conductivity; the thin film grown at showed 0.02 S/cm.

Ferromagnetic properties of epitaxial La2NiMnO6 thin films grown by pulsed laser deposition

La 2 NiMnO 6 (LNMO) thin films were fabricated on (100) oriented SrTiO3 single crystal substrates by pulsed laser deposition method. The film growth conditions were found to significantly affect the magnetic moment and ferromagnetic transition temperature of LNMO films. Epitaxial LNMO films exhibiting the ferromagnetism equivalent to that of bulk polycrystal were grown only in such a narrow region of growth temperature and oxygen pressure that stabilized Ni2+–O–Mn4+ superexchange ferromagnetic interaction. Out of this narrow region, the ferromagnetism is significantly suppressed by the appearance of secondary phases, locally disordered Ni and Mn ions, and oxygen vacancies.

Defects and transport in complex oxide thin films

Epitaxial oxide thin films are at the heart of new “oxide electronic” applications, such as excitonic ultraviolet light-emitting diodes and resistive switching memories. Complex oxide films are often grown by pulsed laser deposition (PLD) because the technique is believed to be material agnostic. Here, we show that one of the fundamental premises used to justify the use of PLD, that material is transferred from an ablation target to the film without stoichiometry deviations, is incorrect even when no volatile elements are involved. Even more importantly, the commonly used solution of increasing the laser energy density above a material-specific threshold value to obtain stoichiometric films cannot be used in the case of low carrier density systems such as SrTiO3, where even minute 1018 cm−3 order cation nonstoichiometry can have a dramatic effect on transport. Lattice parameter deviations in oxide films, which are often incorrectly ascribed to oxygen loss, correlate very well with cation nonstoichiometry. We show that proper simultaneous choice of ablation laser fluence and ablation area is essential and often more important than the growth temperature and oxygen pressure for obtaining bulklike properties in oxide heterostructures.

Structural, optical and electrical properties of In doped CdO thin films for optoelectronic applications

Thin films of indium doped cadmium oxide were deposited on quartz substrate using pulsed laser deposition technique. The effect of growth temperature and partial oxygen pressure on structural, optical and electrical properties was studied. We find that the optical transparency of the films largely depends on the growth temperature, while partial oxygen pressure has virtually no effect on the transparency of the films. Electrical properties are found to be sensitive to both the growth temperature and oxygen pressure. It is observed that conductivity and carrier concentration decreases with temperature. The film grown at 200 °C under an oxygen pressure of 5.0 × 10 − 4 mbar shows high mobility (155 cm 2/V s), high carrier concentration (1.41 × 10 21 cm 3), and low resistivity (2.86 × 10 − 5 Ω cm).

Investigation of oxygen growth pressure effects on TiO2−δ:Co

We find that depending on the oxygen pressure during growth (PO2), the TiO2−δ:Co films show dramatically different magnetic behaviors. The magnetic properties are dominated by cobalt nanoparticles and are sensitive to the nanoparticle size. Hopping transport behavior expected in multiphase granular metal systems is observed for most of the samples in the measured temperature range and the linear I-V regime. Concomitantly, voltage induced tunneling conduction is observed in high electrical fields (nonlinear I-V regime) and at very low temperature (0.35K). Cross sectional transmission electron microscopy images provide further corroboration of the multiphase structure of these materials.

Structural and Magneto-transport Properties of Cr-doped In2O3 Diluted Magnetic Semiconductors

AbstractWe report the experimental study of the structural and magnetotransport properties of chromium-doped indium oxide (In2O3:Cr) thin films using x-ray diffractometer, and by measuring the resistivity and Hall effect as a function of temperature in various magnetic fields. The In2O3:Cr diluted magnetic semiconductor thin films were grown under different partial oxygen pressures (Po2) on sapphire substrates using pulsed laser deposition (PLD) technique. Observed expansions in lattice parameter and crystal size in these films with increase in oxygen growth pressure are traceable to the reduction in oxygen vacancies. A redshift of the absorption edges of the samples with increase in oxygen growth pressure is attributed to the significant improvement in crystallinity. The exchange interaction between the electron spins in the conduction band and the spins of the Cr 3d electrons was evident in the anomalous Hall effect (AHE), which persisted up to 300 K. An analysis of the dc electrical transport in the films was carried out using hopping conduction and ionized impurity scattering models.

Structural, optical and electrical characterization of highly conducting Mo-doped In 2O 3 thin films

Highly conducting and transparent thin films of molybdenum-doped indium oxide were deposited on quartz by pulsed laser deposition. The effect of growth temperature and oxygen partial pressure on the structural, optical and electrical properties was studied. We find that the film transparency depends on the growth temperature. The average transmittance of the films grown at different temperatures is in range of 48–87%. The X-ray diffraction results show that the films grown at low temperature are amorphous while the films grown at higher temperature are crystalline. Electrical properties are found to be sensitive to both the growth temperature and oxygen pressure. Resistivity of the films decreases from 1.3 × 10 −3 Ω cm to 8.9 × 10 −5 Ω cm while mobility increases from 9 cm 2/V s to 138 cm 2/V s as the growth temperature increases from room temperature to 700 °C. However, with increase in oxygen pressure, resistivity increases but the mobility decreases after attaining a maximum. The temperature-dependent resistivity measurements show transition form semiconductor to metallic behavior. The film grown at 500 °C under an oxygen pressure of 1.0 × 10 −3 mbar is found to exhibit high mobility (250 cm 2/V s), low resistivity (6.7 × 10 −5 Ω cm), and relatively high transmittance (∼90%).

Effect of oxygen partial pressure on the ferromagnetism of Cr-doped TiO2 films

Polycrystalline Cr-doped TiO2 films were fabricated by co-sputtering Cr and TiO2 targets in a pure Ar and O2 mixture with various oxygen partial pressures. Ferromagnetism is observed in all samples and the Curie temperatures are well above 390 K. The saturation magnetization of films shows strong dependence on the oxygen growth pressure while keeping a constant Cr concentration. The ferromagnetism is enhanced in the films deposited at lower oxygen pressures which are thus oxygen deficient, indicating an important role of oxygen vacancies in the ferromagnetic origin of Cr-doped TiO2.

High mobility, transparent, conducting Gd-doped In 2O 3 thin films by pulsed laser deposition

Highly transparent and conducting thin films of gadolinium doped indium oxide, which have high electron mobility, were deposited on quartz substrate to study the effect of growth temperature and oxygen pressure on their structural, optical, and electrical properties. X-ray diffraction study reveals that these films are randomly oriented on the quartz surface. The average particle size of the films grown at 600 °C was calculated to be ∼ 23 nm. The optical transparency of the films increases with an increase in the growth temperature. The film transparency is also found to increase with increased oxygen pressure during deposition. The electrical properties of these films strongly depend on both the growth temperature and the oxygen pressure. Analysis of the electrical data shows that the mobility of the films increases with increase in the growth temperature.

High mobility W-doped In 2O 3 thin films: Effect of growth temperature and oxygen pressure on structural, electrical and optical properties

Highly conducting and transparent thin films of tungsten (W)-doped indium oxide were obtained using pulsed laser deposition to study the effect of growth temperature and oxygen pressure on structural, optical and electrical properties. The transparency of the films is seen to largely depend on the growth temperature. The electrical properties, however, are found to depend strongly on both the growth temperature and the oxygen pressure. High mobility (up to 358 cm 2 V −1 s −1), low resistivity (1.1 × 10 −4 Ω cm), and relatively high transmittance (∼90%) tungsten-doped indium oxide films have been prepared at a growth temperature of 500 °C and an oxygen pressure of 1 × 10 −6 bar.

Structure and chemical properties of molybdenum oxide thin films

Molybdenum oxide (MoO3) exhibits interesting structural, chemical, electrical, and optical properties, which are dependent on the growth conditions and the fabrication technique. In the present work, MoO3 films were produced by pulsed-laser deposition and dc magnetron sputtering under varying conditions of growth temperature (Ts) and oxygen pressure (pO2). The effect of growth conditions on the structure and chemical properties of MoO3 films was examined using x-ray diffraction, reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, and infrared spectroscopic measurements. The analyses indicate that the microstructure of Mo oxide films is sensitive to Ts and pO2. The growth conditions were optimized to produce stoichiometric and highly textured polycrystalline MoO3 films. A comparison of the microstructure of MoO3 films grown using pulsed-laser deposition and sputtering methods is also presented.

Opto-electrical properties of Ti-doped In 2O 3 thin films grown by pulsed laser deposition

By ablating titanium containing In 2O 3 target with a KrF excimer laser, highly conducting and transparent films on quartz were obtained to investigate the effects of growth temperature and oxygen pressure on the structural, optical and electrical properties of these films. We find that the transparency of the films depends more on the growth temperature and less on the oxygen pressure. Electrical properties, however, are found to be sensitive to both the growth temperature and oxygen pressure. We report in this paper that a growth temperature of 500 °C and an oxygen pressure of 7.5 × 10 −7 bar lead to titanium-doped indium oxide films which have high mobility (up to 199 cm 2 V −1 s −1), low resistivity (9.8 × 10 −5 Ω cm), and relatively high transmittance (∼88%).

Nonstoichiometry as a source of magnetism in otherwise nonmagnetic oxides: Magnetically interacting cation vacancies and their percolation

We discuss the physical conditions required for the creation of collective ferromagnetism in nonmagnetic oxides by intrinsic point defects such as vacancies. We use ${\mathrm{HfO}}_{2}$ as a case study because of recent pertinent calculations and observations. It was previously noted theoretically that charge-neutral Hf vacancies in ${\mathrm{HfO}}_{2}$ have partially occupied electronic levels within the band gap, and thus the vacancies carry a nonvanishing local magnetic moment. Such density functional supercell calculations have further shown that two such vacancies interact ferromagnetically if they are separated by up to third-neighbor distance. This suggested to the authors that Hf vacancies could explain the observed collective ferromagnetism in thin ${\mathrm{HfO}}_{2}$ films. Here we use our previously developed more complete methodology [Phys. Rev. Lett. 96, 107203 (2006)] to inquire if such vacancies can lead to collective ferromagnetism. Applying this methodology to ${\mathrm{HfO}}_{2}$, we find the following: (i) Hf vacancies appear in a few possible charge states but not all of these have a local magnetic moment. (ii) We calculate the energy required to form such vacancies in ${\mathrm{HfO}}_{2}$ as a function of the chemical potential and Fermi energy, and from this we compute, as a function of growth temperature and oxygen pressure, the equilibrium concentration of those vacancies that have a nonvanishing local magnetic moment. We find that under the most favorable equilibrium growth conditions the concentration of Hf vacancies with magnetic moment at room temperature does not exceed $6.4\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ (fractional composition of ${x}_{\mathrm{eq}}=2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}%$). (iii) Independently, we calculate the minimum Hf vacancy concentration needed to achieve wall-to-wall percolation in the ${\mathrm{HfO}}_{2}$ lattice, given the range of the magnetic ${V}_{\mathrm{Hf}}\text{\ensuremath{-}}{V}_{\mathrm{Hf}}$ interaction (five neighbors) obtained from our supercell calculations. It turns out that the minimum percolation concentration ${x}_{\mathrm{perc}}=13.5%$ needed for collective ferromagnetism is eight orders of magnitude higher than the equilibrium vacancy concentration ${x}_{\mathrm{eq}}$ in ${\mathrm{HfO}}_{2}$ under the most favorable growth conditions. We conclude that equilibrium growth cannot lead to ferromagnetism and that ferromagnetism can be established only if one beats the equilibrium Hf vacancy concentration during growth by as much as eight orders of magnitude. This paper presents also an Appendix that gives the Monte Carlo--calculated percolation thresholds of various lattices as a function of the percolation radius of the interaction.

Effects of growth temperature and oxygen pressure on the properties of heteroepitaxial ZnO thin films on sapphire (0001) substrates by pulsed laser deposition

AbstractWe report a systematic study on the effect of growth temperature and O2 pressure on the structural, optical, and electrical properties of heteroepitaxial ZnO thin films prepared by pulsed laser deposition on sapphire (0001) substrates. The combination of high growth temperature and low O2 pressure was found to improve the crystalline quality of initial heteroepitaxial ZnO films, which can be attributed to the enhanced surface migration of adatoms and thermal energy. The low‐temperature photoluminescence spectra from ZnO films were dominated by donor‐bound exciton emission with very weak deep level emission. The temperature dependent Hall measurement showed that the films are highly degenerated, mainly due to the high defect density near the interface region. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Magneto-transport Properties of Cobalt doped Indium Oxide Dilute Magnetic Semiconductors

AbstractRecently, oxide-based dilute magnetic semiconductors (DMS) have attracted an immense research interest to the scientists due to the possibility of inducing room temperature ferromagnetism and potential uses in novel spintronic devices. In2O3, a transparent opto-electronic material, is an interesting prospect for spintronics due to its unique combination of magnetic, electrical, and optical properties. High quality thin films of Co-doped In2O3 DMS were grown on quartz substrates using pulsed laser deposition technique. All the films have been characterized using different techniques such as x-ray diffraction, Raman spectroscopy, optical transmission spectroscopy, electrical resistivity, and Hall Effect measurement. The effect of growth temperature and oxygen pressure on the electrical, magnetic, and optical properties of these films have been studied in detail. The optical transparency in all the films is high. It has been observed that the optical transparency depends on growth temperature and oxygen pressure. The electrical parameters such as resistivity, carrier concentration, and mobility strongly depend on both oxygen pressure and growth temperature. The films grown at low temperature are semiconducting in nature while the films grown at high temperature are metallic. Detailed temperature and magnetic field dependent resistivity, magnetoresistance, and Hall effect data will be presented. This work is supported by Research Corporation (award number CC6166).

Electrical and Optical Properties of High Mobility W-doped In2O3 Thin Films

AbstractTransparent conducting oxides (TCO) have been widely used for opto-electronic devices such as light emitting diodes, photo-detectors, touch panels, flat panel displays, and solar cells. Low resistivity, high mobility, and good transparency are the prime requirements for these devices. There is an increasing interest in TCO with high mobility to decrease their electrical resistivity without a significant decrease in the optical transparency. Highly conducting and transparent tungsten doped indium oxide thin films were deposited on quartz substrate by ablating the sintered In2O3 target containing WO3 with a KrF excimer laser (λ = 248 nm and pulsed duration of 20 ns). The effect of growth temperature and oxygen pressure on structural, optical, and electrical properties has been studied. The transparency of the films largely depends on the growth temperature. The electrical properties are found to depend strongly on the growth temperature as well as on oxygen pressure. The temperature dependence resistivity measurement shows the transition from semiconductor to metallic behavior as the growth temperature increases from room temperature to 500 °C. The high mobility (up to 358 cm2V−1s−1), low resistivity (1.1 × 10−4 Ω.cm), and relatively high transmittance of ∼90 % have been observed on the optimized film grown at 500 °C and under oxygen pressure at 1 × 10−6 bar.

A Study of High Quality Al-doped ZnO Thin Films Grown at Low Temperature by Pulsed Laser Deposition

AbstractHighly conducting and transparent Al-doped ZnO (AZO) thin films, which are oriented along c-axis and have wurtzite structure, were grown on quartz substrate at low temperature by pulsed laser deposition. The techniques of x-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), optical transmission spectroscopy (OTS), electrical resistivity, and Hall Effect were used to study the effect of growth temperature and oxygen pressure on the structural, electrical transport, and optical properties of these films. The optical transparency in all the films is high and does not change much with oxygen pressure and growth temperature. However, electrical parameters such as resistivity, carrier concentration, and mobility strongly depend on both oxygen pressure and growth temperature. The temperature dependence resistivity measurement indicates semiconducting behavior of all the films. A detailed study indicates that the films which are highly conducting and transparent correspond to an optimum temperature of 200 °C and an oxygen pressure of 5 × 10−7 bar. Higher transmittance of the AZO films compared with pure ZnO and ITO and comparable mobility make us to suggest that Al-doped ZnO is an excellent material for optoelectronic applications.

High-mobility electronic transport in ZnO thin films

A systematic study of electronic transport properties was carried out for ZnO thin films grown on high-temperature annealed buffer layers of semi-insulating Mg0.15Zn0.85O. As functions of growth temperature and oxygen pressure during laser molecular-beam epitaxy growth, there can be seen optimum growth conditions where gross concentration of intrinsic defects is thought to be reduced. For the best qualified film, Hall mobilities of 5000cm2V−1s−1 at 100K and 440cm2V−1s−1 at 300K were recorded with the residual electron densities of 4×1014 and 9×1015cm−3, respectively.