Liquid Injection Metalorganic Chemical Vapor Research Articles

Epitaxial LiNbO3 growth and layer transfer for thin-film electro-optic modulator realization

The aim of the PhD project is to develop a new trend in modulation system for Exail company: thin film (<1 μm) lithium niobate (LN) electro-optic modulator. It exhibits better performance in term of bandwidth, power consumption and footprint than legacy ones [1-3]. This PhD is a cooperation between Exail photonics which is world-renowned for the performances of their electro-optic modulators and FEMTO-ST institute which can offer the possibility to grow stoichiometric LN thin film by means of direct liquid injection metalorganic chemical vapor deposition (DLI-MOCVD). This cooperation opens the possibility to obtain industrialization of optical device based on CVD LN stoichiometric layers which allow to have enhanced performances such as higher electro-optic coefficient than that of congruent compositions of commercial single crystals. Thus, all steps from MOCVD layer deposition to modulator realization can be done here in Besançon.

Heteroepitaxial growth of Ga2O3 on 4H-SiC by liquid-injection MOCVD for improved thermal management of Ga2O3 power devices

We report on the growth of monoclinic β- and orthorhombic κ-phase Ga2O3 thin films using liquid-injection metal-organic chemical vapor deposition on highly thermally conductive 4H-SiC substrates using gallium (III) acetylacetonate or tris(2,2,6,6-tetramethyl-3,5-heptanedionato) gallium (III). Both gallium precursors produced the β phase, while only the use of the latter led to growth of κ-Ga2O3. Regardless of the used precursor, best results for β-Ga2O3 were achieved at a growth temperature of 700 °C and O2 flows in the range of 600–800 SCCM. A relatively narrow growth window was found for κ-Ga2O3, and best results were achieved for growth temperatures of 600 °C and the O2 flow of 800 SCCM. While phase-pure β-Ga2O3 was prepared, κ-Ga2O3 showed various degrees of parasitic β phase inclusions. X-ray diffraction and transmission electron microscopy confirmed a highly textured structure of β- and κ-Ga2O3 layers resulting from the presence of multiple in-plane domain orientations. Thermal conductivities of 53 nm-thick β-Ga2O3 (2.13 + 0.29/−0.51 W/m K) and 45 nm-thick κ-Ga2O3 (1.23 + 0.22/−0.26 W/m K) were determined by transient thermoreflectance and implications for device applications were assessed. Presented results suggest great potential of heterointegration of Ga2O3 and SiC for improved thermal management and reliability of future Ga2O3-based high power devices.

Thermal stability of rhombohedral α- and monoclinic β-Ga2O3 grown on sapphire by liquid-injection MOCVD

We investigate the thermal stability of single-phase undoped epitaxial rhombohedral α- and bi-axially-symmetric, monoclinic β-Ga2O3 thin films grown on sapphire substrates by liquid-injection metalorganic chemical vapor deposition (LI-MOCVD) by means of in-situ high-temperature X-ray diffraction (HT-XRD) and room temperature (RT) cathodoluminescence (CL). Ga2O3 layers were vacuum annealed up to 1100 °C, while monitoring the respective 303‾0 and 6‾03 reflections of α- and β-phase Ga2O3. α-Ga2O3 layers were found to withstand the vacuum annealing at 700 °C/20 min, 750 °C/10 min, and 800 °C/8 min without notable degradation, however an indication of reversible biaxial in-plane compressive strain was observed for annealing temperatures close to 800 °C. Annealing at temperatures above 825 °C led to complete layer degradation and partial phase transformation to (010) β-Ga2O3. β-Ga2O3 layers showed no notable degradation or structural changes after the annealing at 1100 °C/30 min, however an indication of reversible biaxial in-plane tensile strain was observed for prolonged annealing at 1100 °C. RT CL spectra revealed the Ga2O3 emission consisted of several distinctive luminescence bands (red, green, blue, and two UV bands). Relatively weak but distinctive signal maxima with energy close to the expected bandgap energies of α- and β-Ga2O3, at 5.3 and 5.0 eV, respectively, were observed and attributed to their near band-edge (NBE) emissions.

Conductance anisotropy of MOCVD-grown α-Ga2O3 films caused by (010) β-Ga2O3 filament-shaped inclusions

A significant anisotropy in the electrical conductance was observed in Si-doped α-Ga2O3/sapphire samples grown via liquid-injection metal organic chemical vapor deposition. Additionally to epitaxial α-Ga2O3 diffraction, x-ray diffraction (XRD) revealed maxima related to (010) β-Ga2O3. Transmission electron microscopy, atomic force microscopy (AFM), and Raman spectroscopy of undoped samples with similar XRD pattern confirmed the formation of (010) β-Ga2O3 filaments in the epitaxial α-Ga2O3 film. In Si-doped samples, conductive AFM and temperature-dependent current–voltage measurement on transmission line measurement resistors confirmed, that β-Ga2O3 filaments were responsible for significantly higher conductivity along the α-Ga2O3 direction compared to [0001] α-Ga2O3 direction. Current–voltage measurements of transistor structures suggested semiconducting behavior of the β-Ga2O3 filaments embedded in the highly resistive α-Ga2O3 films.

Structure and Thermal Stability of ε/κ-Ga2O3 Films Deposited by Liquid-Injection MOCVD.

We report on crystal structure and thermal stability of epitaxial ε/κ-Ga2O3 thin films grown by liquid-injection metal-organic chemical vapor deposition (LI-MOCVD). Si-doped Ga2O3 films with a thickness of 120 nm and root mean square surface roughness of ~1 nm were grown using gallium-tetramethylheptanedionate (Ga(thd)3) and tetraethyl orthosilicate (TEOS) as Ga and Si precursor, respectively, on c-plane sapphire substrates at 600 °C. In particular, the possibility to discriminate between ε and κ-phase Ga2O3 using X-ray diffraction (XRD) φ-scan analysis or electron diffraction analysis using conventional TEM was investigated. It is shown that the hexagonal ε-phase can be unambiguously identified by XRD or TEM only in the case that the orthorhombic κ-phase is completely suppressed. Additionally, thermal stability of prepared ε/κ-Ga2O3 films was studied by in situ and ex situ XRD analysis and atomic force microscopy. The films were found to preserve their crystal structure at temperatures as high as 1100 °C for 5 min or annealing at 900 °C for 10 min in vacuum ambient (<1 mBar). Prolonged annealing at these temperatures led to partial transformation to β-phase Ga2O3 and possible amorphization of the films.

Low temperature Direct Liquid Injection MOCVD of amorphous CrCx coatings in large-scale reactors: An original route to nanostructured multilayer coatings

The effect of low temperature deposition on the quality and the microstructure of hard a -CrC x coatings grown by Direct Liquid Injection Metal-Organic Chemical Vapor Deposition (DLI-MOCVD) was investigated. At deposition temperatures higher than 525 °C, the coatings are bi-phased and polycrystalline , essentially composed of Cr 7 C 3 with Cr 3 C 2 as a minor phase. By decreasing the temperature in the 525–350 °C range, they are amorphous and exhibit a monolithic glassy-like microstructure without grain boundary. For temperatures lower than 350 °C, the uniform amorphous microstructure changes for a lamellar multilayer structure, while the composition of the gas phase was kept constant at the inlet of the reactor for all these CVD runs. The origin of this surprising lamellar structure has been investigated. After having discarded the idea of a self-organized multilayer growth, sometimes encountered in CVD processes, evidence was found for rapid changes in the deposition mechanism. They are induced by oscillations of the surface temperature around a critical value due to the regulation of the furnace used for such large-scale reactors. These almost periodic temperature changes lead to modulations in the surface composition of nutrient species, and subsequently, to the growth of multilayers. The individual composition of lamellae changes regularly, while the overall composition of the coatings remains identical to that of uniform monolithic coatings. For growth conditions leading to local temperature close to the critical value, a regular and controlled nanostructuring can be obtained with a period close to a hundred nanometers. Similar to monolithic a -CrC x coatings, these a -CrC x multilayer coatings exhibit a good barrier behavior against high temperature oxidation, according to the test performed. As future prospects, the main interest for these lamellar coatings could be their mechanical properties thanks to the numerous interfaces capable of deflecting and dissipating the propagation of cracks. • Chromium carbide coatings are deposited by DLI-MOCVD at very low temperatures. • A lamellar microstructure forms at temperatures as low as 325 °C. • Oxidation barrier behavior is fully conserved with the multilayer structure. • Changes in temperature and reaction mechanisms explain the lamellar growth.

Engineering Copper Adhesion on Poly-Epoxy Surfaces Allows One-Pot Metallization of Polymer Composite Telecommunication Waveguides

Mass gain in the aerospace sector is highly demandable for energy savings and operational efficiency. Replacement of metal parts by polymer composites meets this prerequisite, provided the targeted functional properties are recovered. In the present contribution, we propose two innovative and scalable processes for the metallization of the internal faces of carbon fiber reinforced polymer radiofrequency waveguides foreseen for implementation in telecommunications satellites. They involve sequential direct liquid injection metalorganic chemical vapor deposition of copper and cobalt. The use of ozone pretreatment of the polymer surface prior deposition, or of cost effective anhydrous dimethoxyethane as solvent for the injection of the copper precursor, yield strongly adherent, 5 µm Cu films on the polymer composite. Their electrical resistivity is in the 4.1–5.0 μΩ·cm range, and they sustain thermal cycling between −175 °C and +170 °C. Such homogeneous and conformal films can be obtained at temperatures as low as 115 °C. Demonstration is achieved on a polymer composite waveguide, composed of metallized 60-mm long straight sections and of E-plane and H-plane elbows, that paves the way towards the metallization of scale one devices.

Growth of α- and β-Ga2O3 epitaxial layers on sapphire substrates using liquid-injection MOCVD

Ga2O3, a wide-bandgap semiconductor material, offers a great potential for power and high-voltage electronic devices. We report on the growth of undoped α- and β-phase Ga2O3 using liquid-injection metal-organic chemical vapor deposition (LI-MOCVD) on sapphire substrates. Using the same precursor (gallium acetylacetonate) and deposition temperature of 700 °C, the phase selection was controlled by the sapphire substrate orientation, where the growth of α- and β-phase Ga2O3 was achieved on m- and c-plane surface, respectively. As deduced from x-ray diffraction, α-Ga2O3 films show epitaxial character, while β- Ga2O3 films exhibit highly textured structure. Oxygen flow was also found to have a strong impact on the phase purity of α-Ga2O3 for the flow rates examined. Optical and electrical properties of the layers grown at different oxygen flow rates were also studied systematically. LI-MOCVD growth of α-phase Ga2O3 layers at relatively high deposition temperature widens the high-temperature processing of the Ga2O3-based electronic and optoelectronic devices.

Structure and Magnetic Properties of Nd0.88MnO3 Films Grown on SrTiO3 (100) Substrates by Liquid-Injection MOCVD

In this study, we investigated the structure and magnetic properties of Nd0.88MnO3 (NMO) perovskite thin-film layers by liquid-injection metalorganic chemical vapor deposition (MOCVD) tried on SrTiO3 (STO) (100) substrates. The structural examinations showed that the growing film was amorphous. It changed to the crystalline phase after being annealed at 900°C in air for 24 h. A minor secondary phase identified as Mn3O4 appeared. The film was subjected to in-plane (IP) tensile stress leading to a contraction of the film’s out-of-plane (OOP) lattice parameters. The orientation relationships for the film structure are described near the interface as $$ \left[ {10\bar{1}} \right] $$ NMO// $$ \left[ {100} \right] $$ STO and $$ \left[ {010} \right] $$ NMO// $$ \left[ {001} \right] $$ STO. The NMO thin film showed ferromagnetic ordering with a transition temperature TC = 85 K. The large bifurcation between ZFC and FC curves with a cusp at Tf = 53 K; and an irreversible temperature Tirr = 48 K proves that the spin-glass behavior with long-range ferromagnetic order (Mn3+-O2−-Mn4+) co-exists in NMO thin films. The magnetic easy axis corresponded to the surface normal.

Black Co oxides coatings for thermosensitive polymer surfaces by low-temperature DLI-MOCVD

Black coatings are deposited at low temperature in order to enable the functionalization of thermosensitive substrates, such as epoxy-based carbon fiber reinforced polymers (CFRP). The direct liquid injection metalorganic chemical vapor deposition of Co oxide films is performed with the dicobalt octacarbonyl precursor, Co2(CO)8, in the temperature range 50°C–160°C, on Si substrates, first. Films morphology can be described by a dense sublayer on which the typical “cauliflower” microstructure grows, with a large amount of voids and open porosity. We obtain nanocrystalline CoO in the deposition temperature range 50°C–125°C, and nanocrystalline (CoO+Co3O4) above 125°C. The bulk composition of the films is Co(45)O(45)C(10). Over the deposition temperatures tested, films processed at 125°C repetitively show the lowest reflectivity in the visible range. An important role in the optical reflectivity is attributed to the carbon content, although it is not possible to decorrelate microstructural changes from the carbon elimination in calcination experiments. Finally, we reproduce the above-mentioned results with success on CFRP substrates, and demonstrate the applicability of the process on thermosensitive composite parts with results comparable to the state-of-the-art in the visible range.

Chromium Carbide Growth by Direct Liquid Injection Chemical Vapor Deposition in Long and Narrow Tubes, Experiments, Modeling and Simulation

Chromium carbide layers were deposited using liquid-injection metal-organic chemical vapor deposition inside long (0.3 to 1 m) and narrow (8 to 24 mm in diameter) metallic tubes. The deposition was carried out using a molecular single-source, bis(benzene)chromium (BBC), as representative of the bis(arene)metal family diluted in toluene and injected with N2 as carrier gas. A multicomponent mass transport model for the simulation of the coupled fluid flow, heat transfer and chemistry was built. The kinetic mechanism of the growth of CrCx films was developed with the help of large-scale experiments to study the depletion of the precursors along the inner wall of the tube. The model fits well in the 400–550 °C temperature range and in the 1.3 × 102 to 7 × 103 Pa pressure range. The pressure is shown to have a pronounced effect on the deposition rate and thickness uniformity of the resulting coating. Below 525 °C the structure, composition and morphology of the films are not affected by changes of total pressure or deposition temperature. The coatings are amorphous and their Cr:C ratio is about 2:1, i.e., intermediate between Cr7C3 and Cr3C2. The model was applied to the design of a long reactor (1 m), with a double injection successively and alternatively undertaken at each end to ensure the best uniformity with sufficient thickness. This innovative concept can be used to optimize industrial deposition processes inside long and narrow tubes and channels.

Up-conversion luminescence in Er/Yb-doped YF3 thin films deposited by PLI-MOCVD

We have studied the NIR (near infrared) to visible up-conversion of Er/Yb co-doped YF3 thin films prepared by PLI-MOCVD (pulsed liquid injection metal-organic chemical vapor deposition). Violet, strong green, as well as red emission bands corresponding to intra-4f transitions in Er3+ were observed under 972nm excitation. The up-converted emission was studied as a function of the Yb concentration and in doing so, a change in the red/green emission intensity ratio was observed. We attributed this, on one hand, to an Er-to-Yb back transfer corresponding to 4S3/2 → 4I13/2:2F7/2 → 2F5/2, which starts to occur at increasing Yb concentrations. As a consequence, the red emission is shown to be enhanced through an upward energy transfer 4I13/2 → 4F9/2. On the other hand the depopulation of 4S3/2 is also related to an upward transfer from Yb to Er corresponding to transition 2F5/2 → 2F7/2 :4S3/2 → 4G9/2 which is enhanced by an increasing Yb concentration. We performed power-dependent up-conversion luminescence measurements to confirm the proposed excitation mechanisms. Finally, lifetimes of the intermediate states 4S3/2 and 4F9/2 were determined, to show the influence of the Yb concentration on the relaxation processes in Er3+.

Modeling a MOCVD process to apply alumina films on the inner surface of bottles

Deposition inside a cavity with a narrow neck, i.e. a hollow body, is a challenge, in particular for the supply and the evacuation of the reactive phase and of the effluents through the same entrance. High gradients (pressure, velocity, species concentrations) and important convective mechanisms related to the impacting jet of the gaseous phase on the bottom inner wall of the cavity are created in that region. Given the increasing number of experimental parameters, modeling helps efficient process optimization with better understanding of physical and chemical phenomena occurring inside the hollow body. This study presents a numerical modeling using the CFD code Fluent to simulate a direct liquid injection metalorganic chemical vapor deposition of amorphous alumina coatings from aluminum tri-isopropoxide (ATI) on the inner walls of a glass bottle. The model is used to predict local profiles of gas velocity, temperature and species concentrations into the reactor as well as local growth rate based on an apparent heterogeneous kinetic law of ATI decomposition. Comparison with experimental thickness profiles allows validating the model and leads to a better insight in the phenomena which impact film thickness inhomogeneity along the inner surface. The model contributes to the improvement of the reactor configuration by increasing the distance between nozzle and bottle and the outlet section of the nozzle.

Growth and structural characterization of YMnO3 thin films grown by pulsed liquid injection MOCVD on Si and SrTiO3 substrates

Optimum parameters for the growing of YMnO3 films by pulsed liquid injection metalorganic chemical vapor deposition have been studied. Si substrates were used for the optimization of the deposition process. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that polycrystalline single phase YMnO3 films can be obtained for an optimal ratio of Y and Mn on the injected solution and either amorphous, metastable orthorhombic, and/or hexagonal YMnO3 phases can be obtained depending on the deposition temperature and precursors ratio. In a second stage, YMnO3 films were grown on SrTiO3 substrates. Pure epitaxial orthorhombic YMnO3 phase was confirmed by XRD. The films microstructure, characterized by scanning electron microscopy and TEM, shows a columnar growth. Each columnar grain grows epitaxially with three possible orientations.

Thermal Stability of Neodymium Aluminates High‐κ Dielectric Deposited by Liquid Injection MOCVD Using Single‐Source Heterometallic Alkoxide Precursors

Thin films of neodymium aluminate (NdAlOx) have been deposited by liquid injection metalorganic chemical vapor deposition (MOCVD) using the bimetallic alkoxide precursor [NdAl(OPri)6(PriOH)]2. The effects of high‐temperature postdeposition annealing on NdAlOx thin films are reported. The as‐deposited thin films are amorphous in nature. X‐ray diffraction (XRD) and medium energy ion scattering (MEIS) show, respectively, no crystallization or interdiffusion of metal ions into the substrate after annealing at 950°C. The capacitance‐voltage (C-V) and current‐voltage (I-V) characteristics of the thin films exhibited good electrical integrity following annealing. The dielectric permittivity (κ) of the annealed NdAlOx was 12, and a density of interface states at flatband (Dit) of 4.01 × 1011 cm−2 eV−1 was measured. The deposited NdAlOx thin films are shown to be able to endure high‐temperature stress and capable of maintaining excellent dielectric properties.

High-yield, high-throughput synthesis of germanium nanowires by metal–organic chemical vapor deposition and their functionalization and applications

In this study, a direct liquid-injection metal–organic chemical vapor deposition (LIMOCVD) is developed as a novel synthetic method for high-yield, large-scale synthesis of Ge nanowiresvia vapor–liquid–solid (VLS) growth at temperatures ranging from 390 to 480 °C at atmospheric pressure. Among the precursors tested, including diphenylgermane (DPG), n-butylgermane (NBG), and tetraethylgermane (TEG), DPG exhibited the most suitable reactivity for LIMOCVD nanowire reactions. While using DPG as a precursor, the yields of Ge nanowires by VLS growth can reach up to ∼30%. As a proof-of-concept for scale-up synthesis, sub-gram quantities of Ge nanowires were produced by consecutive injections of precursor solution. The Ge wires were passivated by an alkanethiol monolayer which gives rise to stability, oxidation resistance and significantly improved dispersibility in organic solvents. Nanowire solutions could be used as inks for applications in many fields. For example, bendable, thickness-tunable Ge nanowire fabrics were fabricated from the inks. The LIMOCVD-VLS growth could potentially serve as a facile and reliable method for industrial-scale production of Ge nanowires due to its superior synthetic capacity and low manufacturing cost.

Malonate complexes of dysprosium: synthesis, characterization and application for LI-MOCVD of dysprosium containing thin films

A series of malonate complexes of dysprosium were synthesized as potential metalorganic precursors for Dy containing oxide thin films using chemical vapor deposition (CVD) related techniques. The steric bulkiness of the dialkylmalonato ligand employed was systematically varied and its influence on the resulting structural and physico-chemical properties that is relevant for MOCVD was studied. Single crystal X-ray diffraction analysis revealed that the five homoleptic tris-malonato Dy complexes (1-5) are dimers with distorted square-face bicapped trigonal-prismatic geometry and a coordination number of eight. In an attempt to decrease the nuclearity and increase the solubility of the complexes in various solvents, the focus was to react these dimeric complexes with Lewis bases such as 2,2'-biypridyl and pyridine (6-9). This resulted in monomeric tris-malonato mono Lewis base adduct complexes with improved thermal properties. Finally considering the ease of synthesis, the monomeric nature and promising thermal characteristics, the silymalonate adduct complex [Dy(dsml)(3)bipy] (8) was selected as single source precursor for growing DySi(x)O(y) thin films by liquid injection metalorganic chemical vapor deposition (LI-MOCVD) process. The as-deposited films were analyzed for their morphology and composition by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, Rutherford backscattering (RBS) analysis and X-ray photoelectron spectroscopy.

Chemical vapor deposition and characterization of high-k BaHf1−xTixO3 dielectric layers for microelectronic applications

Possibilities to grow high-k BaHf1−xTixO3 layers were investigated by pulsed liquid injection metal-organic chemical vapor deposition technique. Ba(thd)2 (thd=2,2,6,6-tetramethylheptane-3,5-dionate), Hf(thd)4, and Ti(OiPr)2(thd)2 were used as precursors, toluene as solvent, and Si(100) as substrate. The influence of solution composition and deposition temperature on crystallization and elemental and phase compositions of Ba–Hf–Ti–O layers was investigated. BaHf1−xTixO3 layers with x∼0–0.5 may be obtained at 600–650 °C, whereas the lower deposition temperature (500–550 °C) resulted in crystallization of the dominating orthorhombic BaCO3 phase in deposited films. Films were characterized by x-ray diffraction, atomic force microscopy, and scanning electron microscopy. Electrical measurements were performed for deposited thin films in view of storage capacitor applications of BaHf1−xTixO3 films in dynamic random access memories.

Gadolinium Scandate: Next Candidate for Alternative Gate Dielectric in CMOS Technology?

Gadolinium Scandate: Next Candidate for Alternative Gate Dielectric in CMOS Technology?The films of GdScO3were prepared by liquid injection metal-organic chemical vapor deposition, MOCVD at 600 °C on (100) Si substrate. The as-deposited films were amorphous with a smooth surface and sharp GdScO3/Si interface. X-ray diffraction showed that the amorphous phase is well preserved upon rapid thermal annealing up to 1000 °C. It is shown, that exact stoichiometry of GdScO3is not necessary to achieve dielectric constant above 20.

Structure and defect characterization of multiferroicReMnO3 films and multilayers by TEM

Epitaxial rare earth manganite thin films (ReMnO3;Re = Tb, Ho, Er, and Y) and multilayers were grown by liquid injection metal organicchemical vapor deposition (MOCVD) on YSZ(111) and the same systems were grownc-oriented on Pt(111) buffered Si substrates. They have been structurally investigated byelectron diffraction (ED) and high resolution transmission electron microscopy(HRTEM). Nanodomains of secondary orientation are observed in the hexagonalYMnO3 films. They are related to a YSZ(111) and Pt(111) misorientation.The epitaxial film thickness has an influence on the defect formation.TbO2 andEr2O3 inclusions areobserved in the TbMnO3 and ErMnO3 films respectively. The structure and orientation of these inclusions are correlated to theresembling symmetry and structure of film and substrate. The type of defect formed in theYMnO3/HoMnO3 andYMnO3/ErMnO3 multilayers is also influenced by the type of substrate they are grown on. In our work,atomic growth models for the interface between the film/substrate are proposed andverified by comparison with observed and computer simulated images.