Pulsed Metalorganic Chemical Vapor Deposition Research Articles

Study of AlN Epitaxial Growth on Si (111) Substrate Using Pulsed Metal–Organic Chemical Vapour Deposition

A dense and smooth aluminium nitride thin film grown on a silicon (111) substrates using pulsed metal–organic chemical vapor deposition is presented. The influence of the pulsed cycle numbers on the surface morphology and crystalline quality of the aluminium nitride films are discussed in detail. It was found that 70 cycle numbers produced the most optimized aluminium nitride films. Field emission scanning electron microscopy and atomic force microscopy images show a dense and smooth morphology with a root-mean-square-roughness of 2.13 nm. The narrowest FWHM of the X-ray rocking curve for the AlN 0002 and 10–12 reflections are 2756 arcsec and 3450 arcsec, respectively. Furthermore, reciprocal space mapping reveals an in-plane tensile strain of 0.28%, which was induced by the heteroepitaxial growth on the silicon (111) substrate. This work provides an alternative approach to grow aluminium nitride for possible application in optoelectronic and power devices.

Enhancing the quality of homoepitaxial (−201) β-Ga2O3 thin film by MOCVD with in situ pulsed indium

This article innovatively uses pulsed metal-organic chemical vapor deposition technology to optimize the quality of β-Ga2O3 thin films on (−201) β-Ga2O3 homo-substrate using indium pulse-assisted technology. The results demonstrate that the pulsed indium-assisted method, when compared with the traditional indium-assisted method, effectively suppresses the desorption of Ga2O, enhances the flatness of the β-Ga2O3 film, and reduces the surface roughness from 34.8 to 0.98 nm. The optimized single crystalline β-Ga2O3 film was grown with pulsed-indium, and the full width at half maximum of x-ray diffraction rocking curve was 30.42 arc sec, smaller than that of the continuous indium β-Ga2O3 (56.1 arc sec). In combination with the x-ray photoelectron spectroscopy O1s split-peak fitting analysis, the relative content of oxygen vacancies in the film was significantly reduced by pulsed indium-assisted method. The Hall mobility of films assisted by pulsed-indium is approximately 14 times higher than that of films assisted by traditional indium. The pulsed indium technology provides an idea for homoepitaxial growth of high-quality β-Ga2O3 films.

Van der Waals Epitaxy, Superlubricity, and Polarization of the 2D Ferroelectric SnS.

Tin monosulfide (SnS) is a two-dimensional layered semiconductor that exhibits in-plane ferroelectric order at very small thicknesses and is of interest in highly scaled devices. Here we report the epitaxial growth of SnS on hexagonal boron nitride (hBN) using a pulsed metal-organic chemical vapor deposition process. Lattice matching is observed between the SnS(100) and hBN{11̅0} planes, with no evidence of strain. Atomic force microscopy reveals superlubricity along the commensurate direction of the SnS/hBN interface, and first-principles calculations suggest that friction is controlled by the edges of the SnS islands, rather than interface interactions. Differential phase contrast imaging detects remnant polarization in SnS islands with domains that are not dictated by step-edges in the SnS. The growth of ferroelectric SnS on high quality hBN substrates is a promising step toward electrically switchable ferroelectric semiconducting devices.

Optimization quality for indium pulse-assisted of β-Ga2O3 thin film on sapphire surface

In the field of wide-bandgap semiconductors, fabricating high quality β-Ga2O3 films on heterogeneous substrates remains a tremendous challenge. This article innovatively uses pulsed metal-organic chemical vapor deposition (MOCVD) technology to optimize the quality of β-Ga2O3 thin film on sapphire substrates using indium pulse-assisted technology. The findings indicate that full width at half maximum of the (−201) β-Ga2O3 crystal plane orientation is reduced by 2700 arcsec after pulsed indium-assisted. The addition of pulsed indium atoms effectively suppresses the desorption of low oxide Ga2O, improving the flatness of β-Ga2O3 films surface and reduced the surface roughness from 30.1 nm to 5.4 nm. Moreover, the UV–Visible transmittance of the film exceeds 80%, accompanied by an increase in bandwidth. In combination with the XPS O1s split-peak fitting analysis, the quality of the films was optimized by using pulsed indium-assisted, resulting in a reduction in the relative content of oxygen vacancies in the film. The pulsed indium technology provides a new idea for heteroepitaxy growth of high quality β-Ga2O3 films.

Deterministically-grown GaN microrods on a mask-free plateau patterned substrate

In this study, a polished plateau-patterned sapphire substrate (PP-PSS) was developed to grow epitaxial GaN microrods using an AlN buffer layer via pulsed metal–organic chemical vapor deposition. The diameter of the plateau region could be easily adjusted in the range of 600–1600 nm by altering the polishing time, allowing the selective growth of the GaN microrods in only the plateau region and subsequent deposition on the AlN layer. The GaN microrod growth mechanism on the PP-PSS was explained using the morphology of the grown GaN microrods. Transmission electron microscopy revealed that the single-crystalline GaN microrods had a GaN (0002) d spacing of 0.263 nm, and a measured lattice constant ratio of the (0001) and (10 1‾ 0) planes of 0.535, which is similar to the theoretical value of 0.532 for a fully relaxed GaN. Through Raman spectroscopy, the GaN microrod E2 (high) mode was 566.70 cm−1, which was shifted by only 0.50 cm−1 compared to that of the strain-free reference. These results suggest that stress-free GaN microrod epitaxial growth is possible on PP-PSS.

A Strategy for Wafer‐Scale Crystalline MoS2 Thin Films with Controlled Morphology Using Pulsed Metal–Organic Chemical Vapor Deposition at Low Temperature

Abstract2D semiconductor materials with layered crystal structures have attracted great interest as promising candidates for electronic, optoelectronic, and sensor applications due to their unique and superior characteristics. However, a large‐area synthesis process for various applications and practical mass production is still lacking. In particular, there is a limitation in that a high process temperature and a very long process time are required to deposit a crystallized 2D material on a large area. Herein, pulsed metal–organic chemical vapor deposition (p‐MOCVD) is proposed for the growth of wafer‐scale crystalline MoS2 thin films to overcome the existing limitations. In the p‐MOCVD process, precursors are repeatedly injected at regular intervals to enhance the migration of precursors on the surface. As a result, crystalline MoS2 is successfully synthesized at the lowest temperature (350 °C) reported so far in a very short process time of 550 s. In addition, it is found that the horizontal and vertical growth modes of MoS2 can be effectively controlled by adjusting key process parameters. Finally, various applications are presented by demonstrating the photodetector (detectivity = 18.1 × 106 at light power of 1 mW) and chemical sensor (response = 38% at 100 ppm of NO2 gas) devices.

Influence of cooling rate on ferroelastic domain structure for epitaxial (100)/(001)-oriented Pb(Zr, Ti)O3 thin films under tensile strain

Epitaxial (100)/(001)-oriented Pb(Zr x Ti1−x )O3 [PZT] films were grown at 700 °C on (100)KTaO3 single crystal substrates by pulsed metalorganic chemical vapor deposition. We investigated the influence of the cooling condition on the ferroelastic domain structure for PZT films under compressive and tensile strains. Under compressive strain, the c-domain fraction (V c ) was not strongly influenced by the cooling rate. On the other hand, changing the cooling rate caused a significant change in V c in the PZT films grown under tensile strain. In addition, a post-annealing step at a certain temperature below the Curie temperature promoted the formation of a c-domain in the a 1/a 2-domain. These results indicate the need to effectively time the formation of the c-domain in the a 1/a 2-domain, which is governed by the growth kinetics. The ferroelastic domain structure under tensile stress is determined by the growth kinetics, while a slow cooling rate leads to a thermodynamically stable domain structure.

Noble Metals for Modern Implant Materials: MOCVD of Film Structures and Cytotoxical, Antibacterial, and Histological Studies.

This work is aimed at developing the modification of the surface of medical implants with film materials based on noble metals in order to improve their biological characteristics. Gas-phase transportation methods were proposed to obtain such materials. To determine the effect of the material of the bottom layer of heterometallic structures, Ir, Pt, and PtIr coatings with a thickness of 1.4–1.5 μm were deposited by metal–organic chemical vapor deposition (MOCVD) on Ti6Al4V alloy discs. Two types of antibacterial components, namely, gold nanoparticles (AuNPs) and discontinuous Ag coatings, were deposited on the surface of these coatings. AuNPs (11–14 nm) were deposited by a pulsed MOCVD method, while Ag films (35–40 nm in thickness) were obtained by physical vapor deposition (PVD). The cytotoxic (24 h and 48 h, toward peripheral blood mononuclear cells (PBMCs)) and antibacterial (24 h) properties of monophase (Ag, Ir, Pt, and PtIr) and heterophase (Ag/Pt, Ag/Ir, Ag/PtIr, Au/Pt, Au/Ir, and Au/PtIr) film materials deposited on Ti-alloy samples were studied in vitro and compared with those of uncoated Ti-alloy samples. Studies of the cytokine production by PBMCs in response to incubation of the samples for 24 and 48 h and histological studies at 1 and 3 months after subcutaneous implantation in rats were also performed. Despite the comparable thickness of the fibrous capsule after 3 months, a faster completion of the active phase of encapsulation was observed for the coated implants compared to the Ti alloy analogs. For the Ag-containing samples, growth inhibition of S. epidermidis, S. aureus, Str. pyogenes, P. aeruginosa, and Ent. faecium was observed.

Heterostructures based on Pd–Au nanoparticles and cobalt phthalocyanine for hydrogen chemiresistive sensors

In this work, the effect of Pd, Au and PdAu nanoparticles on sensor response of cobalt phthalocyanine films to hydrogen was studied. For this purpose, novel heterostructures based on cobalt phthalocyanine and PdAu nanoalloys were obtained by a combination of vacuum thermal evaporation and pulsed metalorganic chemical vapor deposition (MOCVD) and investigated as active layers for hydrogen detection. The structural features and phase composition of the prepared heterostructures were studied by the techniques of X-ray diffraction, transmission electron microscopy and electron diffraction. The concentration of metal nanoparticles in the samples was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The chemiresistive sensor response of CoPc/M (M = Pd, Au, Pd0.2Au0.8 and Pd0.8Au0.2) to hydrogen (100–400 ppm, room temperature) was compared with that of bare CoPc films. It was shown that the sensor response of the investigated heterostructures to hydrogen (300 ppm) increased in the order CoPc (0.2%) < CoPc/Pd0.2Au0.8 (1.9%) ~ CoPc/Au (2.2%) < CoPc/Pd (2.7%) < CoPc/Pd0.8Au0.2 (5.6%).

High-Throughput Growth of Wafer-Scale Monolayer Transition Metal Dichalcogenide via Vertical Ostwald Ripening.

For practical device applications, monolayer transition metal dichalcogenide (TMD) films must meet key industry needs for batch processing, including the high-throughput, large-scale production of high-quality, spatially uniform materials, and reliable integration into devices. Here, high-throughput growth, completed in 12 min, of 6-inch wafer-scale monolayer MoS2 and WS2 is reported, which is directly compatible with scalable batch processing and device integration. Specifically, a pulsed metal-organic chemical vapor deposition process is developed, where periodic interruption of the precursor supply drives vertical Ostwald ripening, which prevents secondary nucleation despite high precursor concentrations. The as-grown TMD films show excellent spatial homogeneity and well-stitched grain boundaries, enabling facile transfer to various target substrates without degradation. Using these films, batch fabrication of high-performance field-effect transistor (FET) arrays in wafer-scale is demonstrated, and the FETs show remarkable uniformity. The high-throughput production and wafer-scale automatable transfer will facilitate the integration of TMDs into Si-complementary metal-oxide-semiconductor platforms.

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.

Charge Separation in Epitaxial SnS/MoS2 Vertical Heterojunctions Grown by Low-Temperature Pulsed MOCVD.

The weak van der Waals bonding between monolayers in layered materials enables fabrication of heterostructures without the constraints of conventional heteroepitaxy. Although many novel heterostructures have been created by mechanical exfoliation and stacking, the direct growth of 2D chalcogenide heterostructures creates new opportunities for large-scale integration. This paper describes the epitaxial growth of layered, p-type tin sulfide (SnS) on n-type molybdenum disulfide (MoS2) by pulsed metal-organic chemical vapor deposition at 180 °C. The influence of precursor pulse and purge times on film morphology establishes growth conditions that favor layer-by-layer growth of SnS, which is critical for materials with layer-dependent electronic properties. Kelvin probe force microscopy measurements determine a built-in potential as high as 0.95 eV, and under illumination a surface photovoltage is generated, consistent with the expected Type-II band alignment for a multilayer SnS/MoS2 heterostructure. The bottom-up growth of a nonisostructural heterojunction comprising 2D semiconductors expands the combinations of materials available for scalable production of ultrathin devices with field-tunable responses.

Morphological, structural, optical, and electrical study of nanostructured thin films: Charge transport mechanism of p-type Co3O4

The normal cubic spinel Co3O4 () is the most stable crystalline cobalt oxide and is a promising material for many applications due to its high abundance, low cost, and low toxicity. Co3O4 is successfully used as magnetic material [1], as supercapacitor [2,3], as electrochromic windows [4], as well as corrosion protective coatings [5]. It is noteworthy that Co3O4 is a direct p-type semiconductor and is extensively studied in photovoltaics cells [6], in gas sensors [7], in anode materials in lithium-ion batteries [8] and in photocatalysis [9]. Low band gap, large surface exchange and high conductivity are essential properties for the achievement of efficient photocatalytic materials. A large variety of physical and chemical deposition methods are available to tailor the films microstructures and their inherent physical and electrochemical properties. In particular, various Co3O4 deposition methods have been reported as epitaxy [10,11], magnetron sputtering [12,13], pulsed laser deposition [6], thermal oxidative decomposition method [4], chemical spray pyrolysis [3,14], sol–gel processes like dip coating [15], metal organic chemical vapor deposition (MOCVD) [16], plasma enhanced MOCVD [9], pulsed liquid injection MOCVD [5], and atomic layer deposition (ALD) [17,18]. Moreover, the electrical properties are strongly related to the deposition method. MOCVD [16] and ALD [18,19] dense thin films show the lowest resistivity ranging from 0.5 to 100 Ω cm, while sol-gel [20], chemical precipitation [21], and spray pyrolysis [3,[22], [23], [24]] deposition methods show lower conductive films with resistivity of about two orders of magnitude higher. The main hypothesis to explain this significant difference is the morphology and the grain size. The conduction paths in the highest conductive Co3O4 thin films is discussed as grain boundaries [18] or through the grains by variable range hopping (VRH) conduction of holes as proposed by Cheng et al. [16]. However, to the best of our knowledge, the latter hypothesis is not demonstrated experimentally using nano-scale characterization. In this context, the main objective of this paper is to investigate the influence of the Co3O4 morphology on the electrical properties at macro and nanoscale.In the following, we study the effect of two substrate temperatures (Ts) of 400 °C and 500 °C on the morphology, on the optical and the electrical properties of ~140-nm-thick Co3O4 films deposited by thermally activated pulsed liquid-gas injection MOCVD.

Chemical Composition, Structure, and Functional Properties of the Coatings of Microchannel Plate Channels

To provide the necessary electrical conductivity of microchannel plates, it is proposed that a thin RuOx film be used by means of its pulsed metalorganic chemical vapor deposition onto the walls of the channels. The chemical composition, structure, electrical conductivity, and secondary electron emission are studied using satellite samples. The RuOx film is shown to have a globular structure with a characteristic size of ~100 nm. The core of each globule (average size, ~21 nm) represents a mixture of the Ru and RuO2 phases with a ratio of nearly 4 : 6. The other part of the globule is amorphous with a Ru : RuO2 ratio of ~5.4 : 4.6. The electrical conductivity of the films has a metallic character. The secondary-electron-emission coefficient of RuOx increases from 2.5 to ~4 after annealing in air at temperatures up to 800°C.

Editors' Choice—Review—Cobalt Thin Films: Trends in Processing Technologies and Emerging Applications

Cobalt metallic films are the subject of an ever-expanding academic and industrial interest for incorporation into a multitude of new technological applications. This report reviews the state-of-the art chemistry and deposition techniques for cobalt thin films, highlighting innovations in cobalt metal-organic chemical vapor deposition (MOCVD), plasma and thermal atomic layer deposition (ALD), as well as pulsed MOCVD technologies, and focusing on cobalt source precursors, thin and ultrathin film growth processes, and the resulting effects on film composition, resistivity and other pertinent properties.

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.

In-plane orientation and composition dependences of crystal structure and electrical properties of {100}-oriented Pb(Zr,Ti)O3 films grown on (100) Si substrates by metal organic chemical vapor deposition

In-plane orientation-controlled Pb(Zrx,Ti1−x)O3 (PZT) films with a thickness of approximately 2 µm and a Zr/(Zr + Ti) ratio of 0.39–0.65 were grown on (100) Si substrates by pulsed metal–organic chemical vapor deposition (MOCVD). In-plane-oriented epitaxial PZT films and in-plane random fiber-textured PZT films with {100} out-of-plane orientation were grown on (100)c SrRuO3//(100)c LaNiO3//(100) CeO2//(100) YSZ//(100) Si and (100)c SrRuO3/(100)c LaNiO3/(111) Pt/TiO2/SiO2/(100) Si substrates, respectively. The effects of Zr/(Zr + Ti) ratio and in-plane orientation on the crystal structure, dielectric, ferroelectric, and piezoelectric properties of the films were systematically investigated. The X-ray diffraction measurement showed that the epitaxial PZT films had a higher volume fraction of (100) orientation than the fiber-textured PZT films in the tetragonal Zr/(Zr + Ti) ratio region. A large difference was not detected between the epitaxial films and the fiber-textured films for Zr/(Zr + Ti) ratio dependence of the dielectric constant, and remanent polarization. However, in the rhombohedral phase region [Zr/(Zr + Ti) = 0.65], coercive field was found to be 1.5-fold different between the epitaxial and fiber-textured PZT films. The maximum field-induced strains measured at 0–100 kV/cm by scanning atomic force microscopy were obtained at approximately Zr/(Zr + Ti) = 0.50 and were about 0.5 and 0.3% for the epitaxial and fiber-textured PZT films, respectively.

Engineering of InN epilayers by repeated deposition of ultrathin layers in pulsed MOCVD growth

Abstract Capabilities of repeated deposition of ultrathin layers by pulsed metalorganic chemical vapor deposition (MOCVD) for improvement of structural and luminescence properties of InN thin films on GaN/sapphire templates were studied by varying the growth temperature and the durations of pulse and pause in the delivery of In precursor. X-ray diffraction, atomic force microscopy, and spatially-resolved photoluminescence (PL) spectroscopy were exploited to characterize the structural quality, surface morphology and luminescence properties. Better structural quality is achieved by using longer trimethylindium pulses. However, it is shown that the luminescence properties of InN epilayers correlate with the pause and pulse ratio rather than with their absolute lengths, and the deposition of 1.5–2 monolayers of InN during one growth cycle is optimal to achieve the highest PL intensity. Moreover, the use of temperature ramping enabled achieving the highest PL intensity and the smallest blue shift of the PL band. The luminescence parameters are linked with the structural properties, and domain-like patterns of InN layers are revealed.

Rapid Wafer-Scale Growth of Polycrystalline 2H-MoS2 by Pulsed Metalorganic Chemical Vapor Deposition.

High volume manufacturing of devices based on transition metal dichalcogenide (TMD) ultra-thin films will require deposition techniques that are capable of reproducible wafer-scale growth with monolayer control. To date, TMD growth efforts have largely relied upon sublimation and transport of solid precursors with minimal control over vapor phase flux and gas-phase chemistry, which are critical for scaling up laboratory processes to manufacturing settings. To address these issues, we report a new pulsed metalorganic chemical vapor deposition (MOCVD) route for MoS2 film growth in a research-grade single-wafer reactor. Using bis(tert-butylimido)-bis(dimethylamido)molybdenum and diethyl disulfide we deposit MoS2 films from ≈ 1 nm to ≈ 25 nm in thickness on SiO2/Si substrates. We show that layered 2H-MoS2 can be produced at comparatively low reaction temperatures of 591 °C at short deposition times, approximately 90 s for few-layer films. In addition to the growth studies performed on SiO2/Si, films with wafer-level uniformity are demonstrated on 50 mm quartz wafers. Process chemistry and impurity incorporation from precursors are also discussed. This low-temperature and fast process highlights the opportunities presented by metalorganic reagents in the controlled synthesis of TMDs.

Effect of in-plane tensile strain in (100)/(001)-oriented epitaxial PbTiO3 films on their phase transition temperature and tetragonal distortion

(100)/(001)-oriented epitaxial lead titanate (PbTiO3) films with various thicknesses were grown on (100) KTaO3 substrates by pulsed metal–organic chemical vapor deposition. The change of crystal structure with film thickness and deposition temperature was investigated. The paraelectric phase of 50 and 1000 nm-thick films had a tensile strain of 0.5% and almost 0% at 700 °C, respectively. The phase change temperature from the paraelectric phase to the ferroelectric phase, the Curie temperature (Tc), increased with the in-plane strain of the paraelectric phase; that is, Tc increased with decreasing film thickness. In contrast, room-temperature tetragonal distortion decreased as the film became thinner. This study reveals the effect of in-plane tensile strain in (100)/(001)-oriented epitaxial PbTiO3 films with higher Tc and smaller tetragonal distortion at room temperature.