Pulsed Injection Metal-organic Chemical Vapor Research Articles

Numerical Study of Growth Rate and Purge Time in the AlN Pulsed MOCVD Process

The relationship between the purge time and the overall growth rate in pulsed injection metal–organic chemical vapor deposition with different V/III ratios is studied by numerical analysis. The transport behavior of TMAl and TMAlNH3 during the process is studied to understand the effect of the adductive reaction. The results show that, as the V/III ratio increases, there is a significant reduction in the average growth rate per cycle, without the addition of a purging H2 pulse between the III and V pulses, due to stronger adductive reaction. The adductive reaction can be reduced by inserting a purging pulse of pure H2 between the III and V pulses, but there is a decrease in the overall growth rate due to the longer cycle time. At smaller V/III ratios, the growth rate decreases with increasing purge times, since the gain in reducing the adductive reaction is offset by the detrimental effect of extending the cycle time. The degree of reduction in the adductive reaction is higher for larger V/III ratios. When the benefit of reducing the adductive reaction overcomes the deficiency of the extending cycle time, a remarkable enhancement of the growth rate can be obtained at high V/III ratios by inserting a pure H2 purge pulse between the III and V pulses. A higher overall growth rate can be achieved at higher V/III ratios by choosing an appropriate purge time.

Influence of Preparation Conditions on Long-Term Stability of Magnetoresistive Properties of Nanostructured La–Sr–Mn–Co–O Films Grown by PI MOCVD

The results of preparation and post-treatment conditions on the long-term stability of Co-substituted nanostructured manganite La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.81</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.19</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.09</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.06</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films are presented. The films were grown on polycrystalline Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrates by pulsed-injection metal-organic chemical vapor deposition technique at 600 °C keeping different growth rates (9, 13, and 27 nm/min), thus inducing different levels of disorder in the films. For comparison, the reference epitaxial films were deposited on the LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrate. The changes of resistivity and magnetoresistance (MR; up to 20 T) during the long-term storage of the films and accelerated aging by annealing the films in O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> or Ar atmosphere at ~100 °C were studied. It was found that the annealing atmosphere and long-term storage have a significant influence on the film resistivity and metal–insulator transition temperature, while MR magnitude is affected insignificantly. The aging effects have the highest influence on the nanostructured film grown at the highest growth rate, while for epitaxial films, the changes are negligible. The observed changes were analyzed using Mott’s variable-range hopping model and explained by oxygen depletion and diffusion in grain boundaries of nanostructured films. The ways to stabilize the main parameters of the manganite–cobaltite films for the development of high magnetic field sensors are discussed.

Morphological Characterization of Calcium Phosphate Particles Obtained by Pulsed-Injection Metal Organic Chemical Vapor Deposition

ABSTRACTAmorphous calcium phosphate particles were synthesized for the first time by the Pulsed Injection Chemical Vapor Deposition technique onto silicon wafers, using Trimethyl Phosphate and Calcium Lactate mixed in a methanol solution as the precursor. The particles were deposited at a substrate temperature of 500, 550, and 600 °C obtaining the best results at 500 °C in terms of nucleation, density, morphology, and Ca/P ratio. The functional groups and vibrational modes, elemental composition, and surface morphology, were studied using Fourier Transform Infrared Spectroscopy, Raman Spectroscopy, and X-ray Energy Dispersion Spectrometry, and Scanning Electron Microscopy, respectively. The presence of the phosphate group characteristic of calcium phosphate was also observed. Uniform growth of the microstructures as the growth time and the temperature of the substrate increases were also observed, together with agglomerates of calcium phosphate in microstructures of 10, 50, and 100 nm in diameter. In these calcium phosphate agglomerates, calcium and phosphorus presence were observed, which is an important feature due to the Ca/P ratio gives information regarding biocompatibility.

PI-MOCVD technology of (La, Sr)(Mn, Co)O3: From epitaxial to nanostructured films

The novel La1-xSrx(Mn1-yCoy)zO3 (LSMCO) films were grown by Pulsed-Injection Metalorganic Chemical Vapor Deposition (PI-MOCVD) technique on different oxide substrates. The structural, transport and magnetic properties of the LSMCO films were investigated in terms of crystal structure, texture, electric and magnetoresistive properties of the films for room temperature applications in magnetic sensing. Additionally, to lattice matching-mismatching approach between the film and the substrate, chemical engineering in form of chemical doping was investigated. A certain Co content (from 0 up to 0.17) was introduced into non-stoichiometric La1-xSrx(Mn1-yCoy)zO3 films (z = 1.15) and revealed that Mn non-stoichiometry as well as Co content, influences the changes of transition from metal to insulator state temperature TMI. For epitaxial films (LSMCO grown on LaAlO3) the transition temperature (TMI) was very close to Curie temperature (Tc – transition from ferromagnetic to paramagnetic state), whereas for nanostructured films (LSMCO on Sapphire and ceramic Al2O3), the transition temperatures were lower in comparison to Tc. It was found, that for all used substrates the transition temperature tends to decrease with the increase of Co-content in the films. The change of magnetoresistance properties with Co-content was observed and revealed highest magnetoresistance values at room temperature for the films with Co-content of ~0.06 up to 2.3 T magnetic field, leading to improved and controlled sensing properties at low magnetic fields.

Metalorganic chemical vapor deposition and investigation of nonstoichiometry of undoped BaSnO3 and La-doped BaSnO3 thin films

Wide bandgap (~3 eV) perovskite transparent conductive oxide material exhibiting superior electric properties is highly desired in today's optoelectronics. Just recently La-doped barium stannate (LBSO) bulk n-type semiconductor with outstanding carrier mobility (~320 cm2 V−1 s−1) at high carrier density (1020 cm−3) has been discovered. Highly conductive thin LBSO film synthesis has been challenging due to large lattice mismatch and nonstoichiometry as being the least investigated. Therefore, in this work, the Pulsed injection metalorganic chemical vapor deposition method was used for the growth of undoped BaSnO3 (BSO) and La-doped BaSnO3 thin films. Film depositions were carried out on monocrystalline LaAlO3, SrTiO3, Al2O3 substrates in wide stoichiometric range. Deviation from stoichiometric composition in BSO (Sn/Ba) and LBSO (Sn/(Ba + La)) had a significant impact on microstructure, optical, and electric properties while maintaining cubic symmetry. Near-stoichiometric films even grown at a high rate of ~10 nm/min showed sufficient electric properties.

Increase of Operating Temperature of Magnetic Field Sensors Based on La–Sr–Mn–O Films With Mn Excess

The results of Mn excess influence on the magnetoresistive properties of nanostructured La1– x Sr x MnyO3±δ films grown on polycrystalline Al2O3 substrates by pulsed-injection metal-organic chemical vapor deposition technique are presented. The electrical transport properties and magnetoresistance of these films were investigated in the temperature range of 77–363 K in pulsed magnetic fields up to 20 T. The results were analyzed from the perspective of using these films for magnetic field sensors operating at high temperatures. It was obtained that the increase of Mn/(La + Sr) ratio from 1.05 to 1.15 leads to the increase of metal–insulator transition temperature from 240 to 270 K. This behavior was associated with the presence of (La + Sr) vacancies, which act as self-dopants. At temperatures higher than 340 K, the highest magnetoresistance values were obtained for films with 15% Mn excess. These results allowed us to produce pulsed magnetic field sensors operating at ambient temperatures up to 90 °C.

Relation between thickness, crystallite size and magnetoresistance of nanostructured La1- x Sr x Mn y O3±δ films for magnetic field sensors.

In the present study the advantageous pulsed-injection metal organic chemical vapour deposition (PI-MOCVD) technique was used for the growth of nanostructured La1−xSrxMnyO3±δ (LSMO) films on ceramic Al2O3 substrates. The compositional, structural and magnetoresistive properties of the nanostructured manganite were changed by variation of the processing conditions: precursor solution concentration, supply frequency and number of supply sources during the PI-MOCVD growth process. The results showed that the thick (≈400 nm) nanostructured LSMO films, grown using an additional supply source of precursor solution in an exponentially decreasing manner, exhibit the highest magnetoresistance and the lowest magnetoresistance anisotropy. The possibility to use these films for the development of magnetic field sensors operating at room temperature is discussed.

Compact Manganite-Graphene Magnetoresistive Sensor

A magnetic field sensor based on a manganite/Al 2 O 3 -substrate/three-layer graphene structure operating in the range of 0.1-20 T was designed and fabricated. The La 0.9 Sr 0.1 Mn 1.2 O 3 (LSMO) manganite film and graphene layers were prepared on the opposite sides of polycrystalline Al 2 O 3 substrate, which enabled scaling of the effective volume of the device to about 0.16 mm 3 . The combination of two materials-graphene with positive magnetoresistance (MR) and manganite with negative MR-led to a significant increase of the response signal and sensitivity compared with individual graphene or manganite sensors. This was achieved by increasing the MR of the individual manganite and graphene elements. The MR of LSMO was increased by using pulsed-injection metal-organic chemical vapor deposition based on two precursor sources with tunable vapor supersaturation and growth rate. The MR of three-layer graphene was optimized by changing the width/length ratio of the rectangular planar configuration and scaling the dimensions from millimeters to few hundred micrometers. The result was a maximal sensitivity of 72 mV/VT in the field range of 1-3 T.

Nanostructured La–Sr–Mn–Co–O Films for Room-Temperature Pulsed Magnetic Field Sensors

The results of Co substitution for Mn in nanostructured La1- x SrxMn1- y Co y O3 films ( $x = 0.2$ ) grown on polycrystalline Al2O3 substrates by pulsed-injection metal-organic chemical vapor deposition technique, are presented. The Co content y in the films was changed as follows: 0; 0.023; 0.053; 0.078. The resistivity ( $\rho )$ dependences on temperature in zero magnetic field was investigated in the temperature range 5–300 K. It was found that the increase in Co content up to 0.078 results in the decrease of metal-insulator transition temperature and increase of the resistivity. The results of nanostructured films are compared with the epitaxial films grown on LaAlO3 substrate keeping the same technological conditions. The magnetoresistance (MR) and MR anisotropy (MRA) were investigated at room temperature (290 K) in permanent magnetic fields up to 2.35 T, and pulsed magnetic fields up to 20 T. It was found that the highest MR values are obtained for the intermediate Co content: $y = 0.053$ , while the MRA decreased with the increase of Co content. The results are discussed within the double-exchange interaction model for the perovskite oxides. The possibility to apply the manganite-cobaltite films for the development of room temperature B-scalar magnetic field sensors is considered.

Magnetoresistance Relaxation Anisotropy of Nanostructured La-Sr(Ca)-Mn-O Films Induced by High-Pulsed Magnetic Fields

The results of investigation of colossal magnetoresistance relaxation in nanostructured La-Sr(Ca)-Mn-O films upon removal of magnetic field pulse are presented. Thin films having thicknesses of 75-350 nm grown by pulsed injection metal-organic chemical vapor deposition technique were studied in pulsed magnetic fields having duration of 0.9 ms and amplitudes of 2-12 T. It was obtained that “fast” relaxation process occurring in hundred microseconds time scale exhibits anisotropy: the magnitude of remnant resistivity is approximately three times smaller and the process is faster when magnetic field is applied perpendicular to the film plane in comparison with in-plane direction. The dynamics of this relaxation process was analyzed using Kolmogorov-Avrami-Fatuzzo model, taking into account nucleation and reorientation of magnetic domains into equilibrium state. The “fast” remnant relaxation was not observed after the application of longer pulses (20 ms) having amplitude of 60 T. Influence of remnant relaxation on operation of B-scalar magnetic field sensors based on nanostructured manganite films is discussed.

Pulsed-injection metal organic chemical vapour deposition for the development of copper silicate and silicide nanostructures

Pulsed-injection metal organic chemical vapour deposition for the development of copper silicate and silicide nanostructures

Phase transformations and selective growth in YMnO3 films

An irreversible phase transformation from amorphous to crystalline orthorhombic YMnO3 (o-YMO) phase takes place in Y–Mn–O films deposited by pulsed-injection metal organic chemical vapor deposition (MOCVD) on Si(100) substrate. This phase transformation was studied through ex-situ and in-situ thermal annealings and the corresponding structural changes were analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. It was shown that it takes place at an almost constant temperature (~700°C) and in a short period of time (~min) and that the o-YMO phase thus obtained is stable at least up to 900°C. We also demonstrate that the selective growth of amorphous, orthorhombic or hexagonal films is made possible by adapting the MOCVD temperature according to the temperature stability region of the different phases.

Metal-organic chemical vapor deposition of high-k dielectric Ce–Al–O layers from various metal-organic precursors for metal–insulator–metal capacitor applications

The possibilities to grow thin layers of high-k dielectric CeAlO3 by pulsed injection metal-organic chemical vapor deposition using different metal-organic (MO) precursors have been investigated. Three pairs of MO precursors were studied for the growth of the films: Ce (IV) and Al(III) 2,2,6,6-tetramethylheptane-3,5-dionates, Ce tetrakis(1-methoxy-2-methyl-2-propoxide)-diethylaluminumethoxide and tris(isopropylcyclopentadienyl)cerium-tris(diethylamino)aluminum. Under optimized conditions, all three pairs of investigated precursors enabled the growth of close to stoichiometric Ce–Al–O films at reasonably low temperatures, 400–450°C, however, crystalline CeAlO3 phase was not present in as-deposited layers. Films were grown on Si(100) and Si(100)/TiN substrates. Two kinds of TiN electrodes were used — amorphous TiN (15–30nm thick) and crystalline TiN (70–100nm thick) layers, grown by chemical vapor deposition and physical vapor deposition techniques, respectively. The pure tetragonal CeAlO3 phase was crystallized in films by a short annealing in Ar or N2 at 800–850°C. Required annealing conditions (temperature and annealing duration) depended on the selected precursors and substrates. Thermomechanical degradation of Si/TiN/Ce–Al–O structures was observed by Scaning Electron Microscopy after the annealing of the samples. Lower degradation degree was observed for structures with a thin amorphous TiN layer.

Structural and magnetic properties of thin films of BaFeO3-δ deposited by pulsed injection metal-organic chemical vapor deposition

Thin films of BaFeO3-δ have been deposited by pulsed injection metal-organic chemical vapor deposition. The films adopt a pseudocubic structure as a result of the match with the cubic structure of the SrTiO3 substrate and the accommodation of a high density of oxygen vacancies. They display antiferromagnetic behavior at room temperature and high electrical resistance. Furthermore, we observed an ageing effect that may be recovered to some extent by annealing in oxygen atmosphere.

Anomalous magnetic field effects during pulsed injection metal-organic chemical vapor deposition of magnetite films

We report on large external magnetic field effects during pulsed injection metal-organic chemical vapor deposition of magnetite films on MgO(001). The application of a 1 T field during the growth process significantly increases the saturation magnetization of magnetite by 150%–220% at a deposition temperature of 550 and 600 °C, while the enhancement of the remanent magnetization is even larger. This anomalous magnetic field effect does not drastically alter the crystalline texture, surface morphology, and film thickness of magnetite, but is explained by a suppression of antiphase-boundary formation during film growth.

Pulsed injection metal organic chemical vapour deposition and characterisation of thin CaO films

Thin films of CaO were grown on silicon (Si) and lanthanum aluminate (LaAlO 3 ) substrates by pulsed injection metal-organic chemical vapour deposition in a vertical injection MOCVD system. Growth parameters were systematically varied to study their effect on film growth and quality and to determine the optimal growth conditions for this material. Film quality and growth rate were evaluated by atomic force microscopy, X-ray diffraction and Rutherford Backscattering Spectroscopy measurements. Optimised conditions allowed growing transparent, single phase films textured along the (0 0 l) direction.

Investigation of alumina–silica films deposited by pulsed injection metal–organic chemical vapour deposition

This work is devoted to deposition of alumina–silica films using an innovative pulsed injection metal organic chemical vapour deposition technique and aluminium tri(iso-propoxide) (Al(i-OPr)3) and tetraethoxysilane (TEOS) as precursors. The deposited aluminium silicate films have been characterised by scanning electron microscopy, infrared spectroscopy, X-ray diffractometry and capacitance–voltage (C–V) measurements. The investigation of the deposition at different Si/Al ratios and substrate temperatures has shown that the growth rate increases with the increase of Al(i-OPr)3 proportion in solution and decreases as the proportion of TEOS increases. We have also shown that aluminium content in the film increases at lower deposition temperatures while silicon content increases at higher temperatures. The permittivity of the films determined from C–V measurements decreases with increasing substrate temperature. It was found that films deposited at substrate temperatures of 600 or 700 °C and with the highest Si/Al ratio have the lowest dielectric permittivity. This research should be useful for further development of MOCVD technology for the deposition of aluminosilicate-based dielectric materials with controlled dielectric permittivity.

Semiconductive Nb-doped BaTiO 3 films grown by pulsed injection metalorganic chemical vapor deposition

Semiconductive Nb-doped BaTiO 3 thin films were grown in situ by pulsed liquid-injection metalorganic chemical vapor deposition on (0 1 2) LaAlO 3 substrates. The films were epitaxially grown, althougth the quality decreased with increasing Nb content. The resistivity was strongly reduced after post-deposition annealing under argon. The room-temperature resistivity reached a minimum of 3 Ω cm for films with ∼2.4 at% Nb content (as measured by EDS). The semiconductive behavior was measured from room temperature up to 470 K and no positive temperature coefficient effect was observed.