High-temperature Chemical Vapor Deposition Research Articles

High-throughput Processes for Industrially Scalable Deposition of Zinc Oxide at Atmospheric Pressure

ZnO films have been grown on a moving glass substrate by high temperature (480 0C) chemical vapour deposition (CVD) and low temperature (200 0C) plasma enhanced CVD (PE-CVD) process at atmospheric pressure. Deposition rates above 7nm/s have been achieved for substrate speeds from 20 to 500mm/min. The conductivity of the films is enhanced by Al doping of CVD ZnO or by exposure to near-UV radiation of PE-CVD ZnO. Both CVD ZnO:Al and UV-exposed PE-CVD i-ZnO films are highly transparent (> 85% in the visible range) and conductive (< 15 Ohm/sq for a thickness above 1200nm). ZnO:Al has been used as front electrode in amorphous silicon (a-Si:H) solar cells while i-ZnO has been applied as electrode in CIGS solar cells, achieving an efficiency of 8% and 15.4%, respectively.

Three-dimensional periodic graphene nanostructures

Graphene is a basic building block for many known and emerging carbon-based materials whose properties largely depend on the way how graphene is structured at the nanoscale. Synthesis of novel three-dimensional (3D) nanostructures of graphene would be an important advance for fundamental research and various applications. In this paper, we discuss the possibility of fabricating complex 3D graphene nanostructures by growing graphene on pre-synthesized nanostructured metal templates by chemical vapor deposition (CVD) and then etching away the metal. In the proof-of-concept experiments, we study this idea using two types of metal nanostructures, inverse opals and slanted nanopillar arrays grown by a glancing angle deposition (GLAD) technique. Due to the elevated temperatures used in typical CVD growth, nanostructures can be easily damaged during the growth process. Therefore, we systematically study the roles of different parameters, such as the composition, morphology and crystallinity of a nanostructured metal, as well as the CVD growth temperature and different carbon sources to grow graphene on metal nanostructures and at the same time preserve their integrity. In particular, we show that nanostructures with large crystalline domains can withstand high temperature CVD, whereas polycrystalline nanostructures, such as nanopillars grown by GLAD, suffer damage even at the low growth temperature of 500 °C. In the case of such thermally sensitive nanostructures, a careful selection of a highly reactive carbon source that could form graphene at lower temperatures becomes crucial. Furthermore, the selection of a metal is also important, as cobalt nanostructures are shown to be more resistant to thermal damage than their nickel counterparts. Finally, we could successfully remove the nanostructured metal templates to form free-standing graphene-based inverse opals and hollow graphene nanopillars. The findings presented in this paper could facilitate synthesis of other 3D graphene nanostructures.

Comparison on Photoluminescence and Magnetism between Two Kinds of Undoped ZnO Nanorods

We carried out a detailed comparison on the defect-related photoluminescence and magnetism in two kinds of undoped ZnO nanorods synthesized by low-temperature chemical bath deposition and high-temperature chemical vapor deposition methods to clarify further the nature of visible emission and d0 ferromagnetism in ZnO based on the fact that these two kinds of ZnO nanorods have significantly different crystallinity and defect states. The results obtained by analyzing X-ray diffraction, electron paramagnetic resonance, and Raman scattering show that the intrinsic ferromagnetism in ZnO nanorods is originated from the single ionized oxygen defects (vacancies and interstitials). Particularly, it is demonstrated that the lattice disorder along the c-axis along with the introduced oxygen interstitials can boost ferromagnetism and induce the red-shift in visible emission.

Influence of the growth temperature of AlN nucleation layer on AlN template grown by high-temperature MOCVD

We studied the influence of the growth temperature of AlN nucleation layer (TNL) on the AlN template grown by high-temperature metal-organic chemical vapor deposition (HT-MOCVD). The AlN templates were characterized by high-resolution X-ray diffractometer, atomic force microscopy and room-temperature Raman scattering spectrometer. The results revealed that the TNL had a direct influence on the quality of the AlN template. By optimizing the TNL at 950°C, we obtained a high-quality AlN template with the full width at half maxima for the (0002) and (10–12) planes of 90″ and 612″, respectively. The AlN template also presented atomic level step with a root mean square (RMS) roughness of 0.133nm. In addition, it performed excellent single crystallographic orientation along the c-axis. The growth evolution of AlN nucleation layer at different TNL was also explained in detail.

Direct synthesis of amorphous carbon nanotubes on Fe76Si9B10P5 glassy alloy particles

A mass of amorphous carbon nanotubes (ACNTs) have been synthesized by chemical vapor deposition of C2H2 directly on Fe76Si9B10P5 glassy alloy particles without the addition of an external catalyst at 550°C for 1h. The ACNTs is 1–5μm in length and 5–30nm in diameter and has a Brunauer–Emmett–Teller surface area of 81.4m2/g. Investigations on the ACNT growth process confirmed that the initial stage for appearance of isolated islands (α-Fe nanoparticles), which might be due to stress and surface breakup generated during high temperature CVD process, would be the decisive step for the ACNT growth.

High temperature chemical vapor deposition of aluminum nitride, growth and evaluation

The application of AlN films in optoelectronics, sensors and high temperature coatings is strongly dependent on the nano-micro-structure of the film, impurity level and defect density. AlN epitaxial thin (0.5–10μm) and thick polycrystalline (>10μm) films were grown on different foreign substrates (sapphire, silicon carbide, graphite) and single AlN crystals by Chemical Vapor Deposition (CVD), also called Hydride Vapor Phase Epitaxy (HVPE), at high temperature (1200–1750°C). In the first part of this paper, polycrystalline growth of thick films (>10μm) prepared at high growth rate (>100μm·h−1) was performed on graphite substrates to study the preferential orientation of the films. AlN/W multilayers were deposited on silicon carbide composites to increase their performance at high temperature in aggressive conditions. Such multilayer materials can be used for the cladding of nuclear fuel. The second part of this paper concerns the characterization of epitaxial films, including their crystalline state, surface morphology, and inherent and thermally induced stress which inevitably leads to high defect densities and even cracking. The full-width at half-maximum (FWHM) of X-ray rocking curves of the grown AlN layers exhibited very large values (several thousand arcsec), and they became steeply deteriorated with increasing growth rate. To improve the crystalline quality of AlN layer, well-known growth techniques, such as multi-step growth using buffer layers, were used at temperatures above 1200°C in order to lower the disorientation to 300arcsec. The applications of such “templates” for deep UV light emitting diodes (UV LED) and surface acoustic wave sensors (SAW) are discussed.

Photo-thermal chemical vapor deposition of graphene on copper

We demonstrate the synthesis of single-layer graphene films on copper by photo-thermal chemical vapor deposition (PTCVD) realized using a rapid thermal processing system typically used in CMOS processing. Influence of the temperature on the low-pressure (10mbar) graphene synthesis using methane precursor was characterized by analyzing the crystalline quality, thickness and electronic properties of the films. Using a growth time of only 60s, for graphene fabricated at 950°C the sheet resistance and mobility show equivalent quality compared to thermal CVD graphene. Moreover, μ-Raman mapping reveals very low defect density and high 2D to G band ratio similar to the fingerprint of exfoliated single-layer graphene. The synthesis process was found to exhibit a threshold at around 900°C at which (and below) the single-layer graphene film does not contain adlayer flakes typically observed in high temperature CVD graphene on copper. Our study shows that PTCVD can be used for the high throughput fabrication of high-quality single-layer graphene on copper and is therefore a promising method while pursuing cost-effective graphene fabrication.

Adhesive bonding and brazing of nanocrystalline diamond foil onto different substrate materials

Diamond coatings are used in heavily stressed industrial applications to reduce friction and wear. Hot-filament chemical vapour deposition (HFCVD) is the favourable coating method, as it allows a coating of large surface areas with high homogeneity. Due to the high temperatures occurring in this CVD-process, the selection of substrate materials is limited. With the desire to coat light materials, steels and polymers a new approach has been developed. First, by using temperature-stable templates in the HFCVD and stripping off the diamond layer afterwards, a flexible, up to 150μm thick and free standing nanocrystalline diamond foil (NCDF) can be produced. Afterwards, these NCDF can be applied on technical components through bonding and brazing, allowing any material as substrate. This two-step process offers the possibility to join a diamond layer on any desired surface. With a modified scratch test and Rockwell indentation testing the adhesion strength of NCDF on aluminium and steel is analysed. The results show that sufficient adhesion strength is reached both on steel and aluminium. The thermal stress in the substrates is very low and if failure occurs, cracks grow undercritically. Adhesion strength is even higher for the brazed samples, but here crack growth is critical, delaminating the diamond layer to some extent. In comparison to a sample directly coated with diamond, using a high-temperature CVD interlayer, the brazed as well as the adhesively bonded samples show very good performance, proving their competitiveness. A high support of the bonding layer could be identified as crucial, though in some cases a lower stiffness of the latter might be acceptable considering the possibility to completely avoid thermal stresses which occur during joining at higher temperatures.

Electrical Characteristics and Fast Neutron Response of Semi-Insulating Bulk Silicon Carbide

The electrical characteristics and fast neutron response of a High Temperature Chemical Vapour Deposition (HTCVD) grown semi-insulating bulk SiC wafer has been measured. Current-Voltage measurements demonstrated a low leakage current in the region of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12v</sup> A with a bulk resistivity of at least 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> Ω.cm. Alpha particle spectroscopy measurements demonstrated an electron charge collection efficiency of up to 90% with reasonable reproducibility of the acquired spectra. Evidence of (incident particle) rate dependent polarisation was seen following a constant applied bias combined with alpha irradiation over a period of time (order of tens of minutes). The ability of the wafer to detect fast neutrons was demonstrated and a comparison drawn with the MCNPX simulated response of a bulk SiC device. Comparing the MCNPX simulated response of a bulk SiC device to that of a silicon device suggests a superior ability to detect fast neutrons with an intrinsic efficiency 1.7 times that of silicon.

Heat-Resistant Co–W Catalytic Metals for Multilayer Graphene Chemical Vapor Deposition

Multilayer graphene (MLG) is expected to be a low-resistance and high-reliability interconnect material replacing copper (Cu) in nanoscale interconnects. Chemical vapor deposition (CVD) on catalytic metals is expected as a practical method for MLG deposition. To obtain high-quality MLG films without catalyst agglomeration by CVD, heat-resistant Co–W catalytic metals were investigated. The agglomeration of the Co–W catalytic metals was suppressed by increasing the W composition; however, MLG deposition was suppressed at the same time. The effects of W addition on the MLG growth were discussed from the viewpoints of the crystallographic change of the Co–W catalysts and chemical reactions. It was found that the Co grain size was reduced and the fcc Co formation was suppressed by W addition. In addition, graphite formation was supposed to be suppressed by W addition owing to the formation of phases other than fcc Co according to the Co–W–C phase diagram. With the optimum W concentration, MLG crystallinity was improved by high-temperature CVD using the heat-resistant Co–W catalytic metals (0.7 at. %) without agglomeration, compared with that in the case of using pure-Co catalysts.

Nonwetting and optical properties of BN nanosheet films

This study begins with a brief discussion on the high-temperature chemical vapor deposition synthesis of transparent boron nitride nanosheet films on silicon/silicon dioxide substrates. The compact nanosheets grew perpendicular to the substrate surface, and the majority of them had thicknesses of less than 5 nm. Ultraviolet-visible spectroscopy measurements demonstrated a wide optical band gap of ∼5·6 eV of nanosheets, and cathodoluminescence spectroscopy showed their strong luminescence emission in the ultraviolet region. The nanorough surface morphology of the films induced nonwetting and self-cleaning features with water-contact angles reaching ∼153°. Such transparent superhydrophobic films can be utilized for the preparation of nonwetting ultraviolet light-emitting surfaces for optoelectronics applications, antifouling surfaces on marine vessels or oil–water separation equipments.

Electron Paramagnetic Resonance Studies of Nb in 6H-SiC

Defects in unintentionally Nb-doped 6H-SiC grown by high-temperature chemical vapor deposition were studied by electron paramagnetic resonance (EPR). An EPR spectrum with a hyperfine (hf) structure consisting of ten equal-intensity lines was observed. The hf structure is identified to be due to the hf interaction between an electron spin S=1/2 and a nuclear spin of 93Nb. The hf interaction due to the interaction three nearest Si neighbors was also observed, suggesting the involvement of the C vacancy (VC) in the defect. Only one EPR spectrum was observed in 6H-SiC polytype. The obtained spin-Hamiltonian parameters are similar to that of the Nb-related EPR defect in 4H-SiC, suggesting that the EPR center in 6H-SiC is the NbSiVC complex in the neutral charge state, NbSiVC0. Photoexcitation EPR experiments suggest that the single negative charge state of the NbSiVC complex is located at ~1.3 eV below the conduction band minimum.

Electron paramagnetic resonance and theoretical studies of Nb in 4H- and 6H-SiC

High purity silicon carbide (SiC) materials are of interest from high-power high temperature applications across recent photo-voltaic cells to hosting solid state quantum bits, where the tight control of electrically, optically, and magnetically active point defects is pivotal in these areas. 4H- and 6H-SiC substrates are grown at high temperatures and the incorporation of transition metal impurities is common. In unintentionally Nb-doped 4H- and 6H-SiC substrates grown by high-temperature chemical vapor deposition, an electron paramagnetic resonance (EPR) spectrum with C1h symmetry and a clear hyperfine (hf) structure consisting of ten equal intensity hf lines was observed. The hf structure can be identified as due to the interaction between the electron spin S = 1/2 and the nuclear spin of 93Nb. Additional hf structures due to the interaction with three Si neighbors were also detected. In 4H-SiC, a considerable spin density of ∼37.4% was found on three Si neighbors, suggesting the defect to be a complex between Nb and a nearby carbon vacancy (VC). Calculations of the 93Nb and 29Si hf constants of the neutral Nb on Si site, NbSi0, and the Nb-vacancy defect, NbSiVC0, support previous reported results that Nb preferentially forms an asymmetric split-vacancy (ASV) defect. In both 4H- and 6H-SiC, only one Nb-related EPR spectrum has been observed, supporting the prediction from calculations that the hexagonal-hexagonal defect configuration of the ASV complex is more stable than others.

Identification of Niobium in 4H-SiC by EPR and &lt;i&gt;Ab Initio&lt;/i&gt; Studies

In unintentionally Nb-doped 4H-SiC grown by high-temperature chemical vapor deposition (HTCVD), an electron paramagnetic resonance (EPR) center with C1h symmetry and an electron spin S=1/2 was observed. The spectrum shows a hyperfine structure consisting of ten equal-intensity hyperfine (hf) lines which is identified as due to the hf interaction between the electron spin and the nuclear spin of 93Nb. An additional hf structure due to the interaction with two equivalent Si neighbors was also observed. Ab initio supercell calculations of Nb in 4H-SiC suggest that Nb may form complex with a C-vacancy (VC) resulting in an asymmetric split-vacancy (ASV) defect, NbSi-VC. Combining results from EPR and supercell calculations, we assign the observed Nb-related EPR center to the hexagonal-hexagonal configuration of the AVS defect in the neutral charge state, (NbSi-VC)0.

Monolayer graphene growth on Ni(111) by low temperature chemical vapor deposition

In contrast to the commonly employed high temperature chemical vapor deposition growth that leads to multilayer graphene formation by carbon segregation from the bulk, we demonstrate that below 600 °C graphene can be grown in a self-limiting monolayer growth process. Optimum growth is achieved at ∼550 °C. Above this temperature, carbon diffusion into the bulk is limiting the surface growth rate, while at temperatures below ∼500 °C a competing surface carbide phase impedes graphene formation.

Tunable morphology and photoluminescence of uniform -Si3N4 microribbons

Tunable morphology and photoluminescence of uniform α-Si3N4 microribbons were obtained by a high temperature chemical vapour deposition method. Long, extra-wide and smooth ribbons with fine crystallinity exhibited variable aspect ratios on the dependence of deposition temperatures. The ribbons were identified to grow along the [210] direction and oxygen component was traced in the crystals. Tunable blue emission was demonstrated for these ribbons. The relationship between the deposition temperature, aspect ratio, oxygen content and photoluminescence are discussed.

In Situ Synthesis of LiFePO4/Carbon Fiber Composite by Chemical Vapor Deposition with Improved Electrochemical Performance

A novel in situ route was employed to synthesize LiFePO4/carbon fiber (CF) composites. The route combined high-temperature solid-phase reaction and chemical vapor deposition (CVD) using LiOH·H2O and FePO4·2H2O as the precursors for LiFePO4 growth and acetylene (C2H2) as carbon source for CF growth. The formation mechanism of the LiFePO4/CF composites was investigated by X-ray diffraction and scanning electron microscopy. The electrochemical performance of the composites was studied by galvanostatic cycling and cyclic voltammetry. The results showed that the in situ CF growth could be realized by the catalytic effect of the Fe2O3 intermediate. The LiFePO4/CF composite with 450 °C CVD reaction showed the best electrochemical performance. This sample exhibited a stable discharge capacity of 122 mA h g–1 at 10C and a slow capacity fade of only 5.5% after 1170 cycles at 1C, indicating an attractive application in high-power Li ion batteries.

Investigation on AlN epitaxial growth and related etching phenomenon at high temperature using high temperature chemical vapor deposition process

Thick AlN layers were grown by high temperature chemical vapor deposition (HTCVD) on 8° off-axis (0 0 0 1) 4H-SiC, on-axis (0 0 0 1) 6H-SiC and on-axis (0 0 0 1) AlN templates between 900 °C and 1600 °C. The experimental set-up consists of a vertical cold-wall reactor working at low pressure in which the reactions take place on a graphite susceptor heated by induction. The reactants used are ammonia (NH 3) and aluminum chlorides (AlCl x ) species in situ formed via Cl 2 reaction with high purity aluminum wire. As-grown AlN layers have been characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Optical Profilometry, Atomic Force Microscopy (AFM) and Raman spectroscopy. In this study, the influence of the deposition temperature and the N/Al ratio in the gas phase is studied in order to stabilize epitaxial growth. The epitaxy on AlN template is favored using a low N/Al ratio in the gas phase and a high temperature above 1400 °C. The crystalline quality of epitaxial AlN layers is found to increase with increasing deposition temperature from 1400 to 1500 °C. Growth rates up to 14 μm h −1 have been reached for epitaxial AlN layers. An important etching phenomenon is also observed at high temperature: apparition of pin holes certainly around threading dislocations at 1400–1500 °C and substrate etching at 1600 °C.

An atomically controlled Si film formation process at low temperatures usingatmospheric-pressure VHF plasma

To grow epitaxial Si films with atomic- and electronic-level perfection,a high-temperature chemical vapor deposition (CVD) process (>1000 °C) has been generally employed. To reduce the growth temperature below600 °C but keeping a high deposition rate, other energy sources than thermal heating are required.Atmospheric pressure plasma CVD (AP-PCVD) is considered to be suitable for fabricatinghigh-quality films at high deposition rates due both to the high radical densityand to the low ion bombardment against the film surface, because the collisionfrequency among ions and neutral atoms is high. The present study focuses on thelow-temperature growth of epitaxial Si, and experimentally demonstrates thatAP-PCVD is capable of growing epitaxial Si films with high perfection applicable forsemiconductor devices. It is found that the pre-growth cleaning of the Si surface byH2 AP plasma is effective to grow high-purity Si films, and that the exposure of a film-growingsurface to AP plasma during growth is important to form particle-free and defect-free Sifilms. From the experimental results and the first-principles molecular dynamicssimulations of surface atomic reactions, it can be mentioned that both H atoms in the APplasma and high-density He atoms having thermal kinetic energy contribute to thereduction of growth temperature by supplying considerable energy to the surface.

Aluminum nitride homoepitaxial growth on polar and non‐polar AlN PVT substrates by high temperature CVD (HTCVD)

AbstractDue to its wide bandgap (6.2 eV), its high thermal conductivity (3.3 WK‐1cm‐1) and high electrical resistivity (1013 Ωcm), AlN is a very expected III‐N semiconductor for applications in high power electronics (HEMTs) and optoelectronics (UV LEDs). In this work, the homoepitaxial growth of aluminum nitride on polar and non‐polar AlN PVT seeds by HTCVD is studied. From our knowledge, the AlN homoepitaxial growth by HVPE or HTCVD on polar and non‐polar bulk AlN substrates has not been reported. The potential of investigation in this new range of experiments conditions, i.e. high temperature and high growth rate, as well as the deposition of non‐polar AlN crystals (Paskova, Phys. Status Solidi B 245(6), 1011 (2008) and Schwarz and Kneissl, Phys. Status Solidi RRL 1(3), A44 (2007) [1, 2]) is very promising for epitaxial growth and could extend the field of applications (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)