Metal-organic Chemical Vapor Deposition Approach Research Articles

A sustainable CVD approach for ZrN as a potential catalyst for nitrogen reduction reaction.

In pursuit of developing alternatives for the highly polluting Haber-Bosch process for ammonia synthesis, the electrocatalytic nitrogen reduction reaction (NRR) using transition metal nitrides such as zirconium mononitride (ZrN) has been identified as a potential pathway for ammonia synthesis. In particular, specific facets of ZrN have been theoretically described as potentially active and selective for NRR. Major obstacles that need to be addressed include the synthesis of tailored catalyst materials that can activate the inert dinitrogen bond while suppressing hydrogen evolution reaction (HER) and not degrading during electrocatalysis. To tackle these challenges, a comprehensive understanding of the influence of the catalyst's structure, composition, and morphology on the NRR activity is required. This motivates the use of metal-organic chemical vapor deposition (MOCVD) as the material synthesis route as it enables catalyst nanoengineering by tailoring the process parameters. Herein, we report the fabrication of oriented and facetted crystalline ZrN thin films employing a single source precursor (SSP) MOCVD approach on silicon and glassy carbon (GC) substrates. First principles density functional theory (DFT) simulations elucidated the preferred decomposition pathway of SSP, whereas ab initio molecular dynamics simulations show that ZrN at room temperature undergoes surface oxidation with ambient O2, yielding a Zr-O-N film, which is consistent with compositional analysis using Rutherford backscattering spectrometry (RBS) in combination with nuclear reaction analysis (NRA) and X-ray photoelectron spectroscopy (XPS) depth profiling. Proof-of-principle electrochemical experiments demonstrated the applicability of the developed ZrN films on GC for NRR and qualitatively hint towards a possible activity for the electrochemical NRR in the sulfuric acid electrolyte.

Low-Temperature and Ammonia-Free Epitaxy of the GaN/AlGaN/GaN Heterostructure

Wide band-gap semiconductors are very attractive because of their broad applications as electronics and optoelectronics materials, GaN-based materials being by far the most promising. For the production of such nitride-based optical and power devices, metal–organic chemical vapor deposition (MOCVD) is routinely used. However, this has disadvantages, such as the large consumption of ammonia gas and the need for a high growth temperature. To go beyond such a limit, in this study we successfully developed a remote plasma MOCVD (RP-MOCVD) approach for the epitaxial growth of high-quality GaN/AlGaN heterostructures on 4H-SiC substrates. Our RP-MOCVD has the advantages of a lower growth temperature (750 °C) compared to the conventional MOCVD route and the use of a remote N2/H2 plasma instead of ammonia for nitrides growth, generating in situ the NHx (x = 0–3) species needed for the growth. As assessed by structural, morphological, optical, and electrical characterization, the proposed strategy provides an overall cost-effective and green approach for high-quality GaN/AlGaN heteroepitaxy, suitable for high electron mobility transistors (HEMT) technology.

Light-Emitting V-Pits: An Alternative Approach toward Luminescent Indium-Rich InGaN Quantum Dots

Realization of fully solid-state white light emitting devices requires high efficiency blue, green, and red emitters. However, challenges remain in boosting the low quantum efficiency of long wavelength group-III-nitride light emitters through conventional quantum well growth. Here, we demonstrate a new direct metal–organic chemical vapor deposition approach to grow In-rich InGaN quantum dots on Si substrates using V-pits, bypassing the need for patterning or unconventional substrates. A correlative nanoscale study on the optical, compositional, and structural properties of intersecting V-pits reveals that the highly textured surface gives rise to localized high intensity red-shifted emission from the apexes of pyramids where InGaN quantum dots spontaneously form. We establish the origin of this efficient long wavelength luminescence to result from both spatially confined higher In-content deposition, as well as smaller bandgap energy basal stacking faults entrapped within a ring of low-emissivity prismatic stacking faults. Our monolithic growth approach on Si would open up new pathways toward attaining CMOS-compatible phosphor-free white light emitting solid-state devices.

MOCVD Growth of Perovskite Multiferroic BiFeO3 Films: The Effect of Doping at the A and/or B Sites on the Structural, Morphological and Ferroelectric Properties

Bismuth ferrite (BiFeO3) materials have been the subject of intense research activity in the last two decades. The great interest arises from the BiFeO3 being one of the rare multiferroic compounds in which ferroelectricity and magnetism coexist at room temperature. To improve these properties several studies have been reported on the doping at the A and/or B sites of the BiFeO3 perovskite structure. In this short review, the attention is focused to the synthesis of BiFeO3 and BiFeO3 doped with Ba or Dy at the A site and Ti at the B site through Metal Organic Chemical Vapor Deposition (MOCVD). The applied MOCVD process consists of an in situ one step approach using a multi‐metal source precursor mixture containing the Bi(phenyl)3 and Fe(tmhd)3 (phenyl = ‐C6H5; H‐tmhd = 2,2,6,6‐tetramethyl‐3,5‐heptandione) as source of Bi and Fe ions. This study evidences the effect of doping on the structural, morphological and piezo/ferroelectric properties of BiFeO3 and doped systems. In summary, this mini‐review illustrates the possibility to apply a simple MOCVD approach to produce good quality pure and doped BiFeO3 films.

Metal-Organic Chemical Vapor Deposition (MOCVD) Synthesis of Heteroepitaxial Pr0.7Ca0.3MnO3 Films: Effects of Processing Conditions on Structural/Morphological and Functional Properties.

Calcium-doped praseodymium manganite films (Pr0.7Ca0.3MnO3, PCMO) were prepared by metal-organic chemical vapor deposition (MOCVD) on SrTiO3 (001) and SrTiO3 (110) single-crystal substrates. Structural characterization through X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) analyses confirmed the formation of epitaxial PCMO phase films. Energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) characterization was used to confirm lateral and vertical composition and the purity of the deposited films. Magnetic measurements, obtained in zero-field-cooling (ZFC) and field-cooling (FC) modes, provided evidence of the presence of a ferromagnetic (FM) transition temperature, which was correlated to the transport properties of the film. The functional properties of the deposited films, combined with the structural and chemical characterization collected data, indicate that the MOCVD approach represents a suitable route for the growth of pure, good quality PCMO for the fabrication of novel spintronic devices.

Perovskite LaCoO3 thin films on single crystal substrates: MOCVD growth and characterization

Metal-Organic Chemical Vapor Deposition (MOCVD) has been applied to the fabrication of lanthanum cobaltite (LaCoO3) films on MgO (001) and LaAlO3 (001) substrates. The films have been deposited using a multi-metal source, consisting of the La (hfa)3•diglyme and Co (tta)2•tmeda (H-hfa=1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme=CH3O-(CH2CH2O) 2CH3, Htta=α-thenoyltrifluoroacetone; tmeda=N,N,N′,N′-tetramethyl-ethylendiammine) precursor mixture. Structural and morphological characterization of films, carried out using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), proved the present MOCVD approach a suitable effective route for the growth of pure LaCoO3 films. Composition and purity has been assessed through energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analyses.

Transparent conductive Ga‐doped ZnO films fabricated by MOCVD

AbstractTransparent conductive oxides (TCOs) are used for a variety of different applications, e.g., in solar cells and light emitting diodes (LEDs). Mostly, sputtering is used, which often results in a degradation of the underlying semiconductor material. In this work we report on a “soft” method for the fabrication of ZnO films as TCO layers by using metal organic chemical vapor deposition (MOCVD) at particularly low temperatures. The MOCVD approach has been studied focusing on the TCO key issues: fabrication temperature, morphology, optical, and electrical properties. Very smooth ZnO films with rms values down to 0.8 nm were fabricated at a substrate temperature of only 300 °C. Ga‐doping is well controllable even for high carrier concentrations up to 2 × 1020 cm−3, which is above the Mott‐density leading to metallic‐like behavior of the films. Furthermore all films show excellent optical transparency in the visible spectral range. As a consequence, our MOCVD approach is well suited for the soft fabrication of ZnO‐based TCO layers.

Selective Synthesis of Hollow and Filled Fullerene-like (IF) WS2 Nanoparticles via Metal–Organic Chemical Vapor Deposition

The synthesis of WS2 onion-like nanoparticles by means of a high-temperature metal–organic chemical vapor deposition (MOCVD) process starting from W(CO)6 and elemental sulfur is reported. The reaction can be carried out as a single-step reaction or in a two-step process where the intermediate products, amorphous WS2 nanoparticles, formed through the high-temperature reaction of tungsten and sulfur in the initial phase of the reaction, are isolated and converted into onion-type WS2 nanoparticles in a separate annealing step. Analysis of the reaction product using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) combined with energy dispersive X-ray spectroscopy (EDX) allowed to optimize the reaction in such a way that filled onion-like structures are formed in a one-step reaction, whereas hollow onion-like structures are obtained by the two-step procedure. A model could be devised that allows us to rationalize the different outcome of the reactions. The MOCVD approach therefore allows a selective synthesis of open and filled fullerene-like chalcogenide nanoparticles.

MOVPE growth of InGaN on sapphire using growth initiation cycles

The worldwide demand for ultra-high-brightness blue and green light emitting devices (LEDs) has driven the development of metalorganic chemical vapor deposition (MOCVD) for Al-Ga-In-N alloy systems towards efficient multiwafer technology. This new MOCVD approach has been developed using a unique growth initiation cycle which provides material of superior quality and increased lateral thickness uniformities in the 7 × 2″ to 15 × 2″ Planetary Reactor ®, which is to our knowledge the largest Nitride MOCVD reactor in the field of successful production of blue LEDs. The MOCVD process, based on a laminar radial two-flow approach will be discussed in detail. The design provides material with abrupt interfaces, also while using different substrates like Al 2O 3, SiC, Si. Wafer rotation is performed by means of Gas Foil Rotation ®. For proper growth initiation for blue-green LED material it is essential that heating from room temperature to 1000 °C can be done in less than 2 min and the cool down from 1000 to 500 °C takes place in 3 min. The growth initiation cycle has been demonstrated to yield device quality GaN with X-ray full width at half maximum (FWHM) of 30 arcsec and excellent photoluminescence (PL) uniformity. Key to the excellent results is the high flexibility of this unique MOCVD process that can be used between 10 and 1000 mbar, a variety of total flow rates and extremely precise temperature control and uniformity across the entire reactor and the substrates, by means of a new multicoil heater system. Using all these flexible parameters in the appropriate way allows to adjust the required growth rate and to obtain the necessary control on In composition in InGaN with the successful demonstration of blue LEDs.