Pressure Chemical Vapor Deposition Research Articles

Stack Diffusion Process for Cost- and Energy-Efficient Boron Emitter Formation

The boron emitter formation for tunnel oxide passivated contact (TOPCon) solar cells faces higher costs compared to the POCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> diffusion for passivated emitter and rear (PERC) solar cells due to the requirement for higher temperatures and longer process times. This work presents an alternative energy-efficient and low cost of ownership boron diffusion approach for TOPCon solar cells, enabling a highly increased throughput compared to the typically used gas phase diffusion. We use an atmospheric pressure chemical vapor deposition borosilicate glass layer as the boron dopant source and combine it with a subsequent thermal anneal in a quartz tube furnace for dopant drive-in. Here, we either use a conventional single-slot quartz boat configuration, or, for highly increased throughput, a vertical wafer stack configuration with the wafer surfaces in direct contact with each other. We show that this approach yields an emitter doping profile comparable to the state-of-the-art gas phase diffusion with sufficient uniformity across the wafer area. We further investigate the emitter dark saturation current densities <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0e</sub> as well as the energy conversion efficiency of TOPCon solar cells fabricated for each configuration and compare the results to those of a BBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> reference process. These solar cells achieve energy conversion efficiencies exceeding 23% for the stack diffusion approach. Additionally, we demonstrate a potential reduction in both the cost of ownership and the specific electricity consumption of the presented approach.

Periodic Spiral Ripples on VS2 Flakes: A Tip-Enhanced Raman Investigation.

Using atmospheric-pressure chemical vapor deposition, we have synthesized vanadium disulfide (VS2) flakes with a metallic 1T phase that display nanoscale spiral surface ripples. To understand the origin of these chiral patterns in these transition metal dichalcogenides, tip-enhanced Raman spectroscopy and Kelvin probe force microscopies were jointly used to investigate their crystal structure, possible oxidation, and electronic properties, respectively. We found that the surface corrugation consists of small crystalline domains with distinct orientations. The change in local orientation is observed concomitantly with a spectral shift of the lattice modes of VS2 and results in the formation of grain boundaries between the domains with distinct orientation. Additionally, the periodic surface structure is modulating the work function of VS2 by 14 meV.

Phase-Field Modeling of Chemical Vapor-Deposited 2D MoSe2 Domains with Varying Morphology for Electronic Devices and Catalytic Applications

Two-dimensional (2D) crystalline growth of transition metal dichalcogenides (TMDs) by atmospheric pressure chemical vapor deposition (APCVD) is highly sensitive to any changes in growth parameters. At an optimized growth temperature and transition metal flux, 2D compact domains grow primarily triangular/hexagonal in shape that transform into dendritic structures at higher transition metal flux. With changes in the local flux (or, local chalcogen-to-transition metal vapor ratio), domain morphologies on the substrate vary with distance for locations away from the center. In this work, phase field simulations are carried out to emulate experimentally observed morphology evolution as a function of transition metal flux. Our model demonstrates the critical roles of precursor flux and attachment time in controlling the domain morphologies which is further established by fractal dimension analysis. Evolution of patterns simulated as a function of flux and attachment time can help to identify more precise combination of growth parameters leading to a specific growth mode. Consistent with the experimental observations, the model also reproduces the interaction among multiple domains. Our findings could be useful for achieving controlled growth of 2D domains with desired shape (compact or dendritic) as required for the next-generation electronic and optoelectronic devices, and efficient catalytic applications.

Boron-carbon-silicon film chemical vapor deposition by boron trichloride, dichlorosilane and monomethylsilane gases

A boron-carbon-silicon film was formed by an atmospheric pressure chemical vapor deposition method using a gas mixture of boron trichloride, dichlorosilane and monomethylsilane in ambient hydrogen at 800–1000 °C. The boron, carbon and silicon concentrations in the obtained film were about 15–30 %, 0–10 % and 50–80 %, respectively. With the increasing monomethylsilane gas flow rate, the carbon and silicon concentrations in the obtained film increased and decreased, respectively. In the obtained film, various chemical bonds between the boron, carbon and silicon existed, except for the carboncarbon bond. The following conclusions were obtained. (i) The carbon atoms existing at the surface have a chemical bond with the boron atoms, but not with the carbon and silicon atoms. (ii) The surface intermediate compound of boron chloride helps incorporating the carbon, while that of dichlorosilane does not. (iii) The etching by the hydrogen chloride gas significantly influenced the film formation process at higher than 900 °C.

Ge Nano-Heteroepitaxy: From Nano-Pillars to Thick Coalesced Layers

Ge epitaxy on nanometer-size Ge pillars was studied in a 300 mm industrial Reduced Pressure-Chemical Vapour Deposition tool. A patterning scheme based on diblock copolymer lithography was used to fabricate honeycombed nanometer-sized Si templates for the hetero-epitaxy of Ge nano-pillars. It was highly selective and uniform at 600°C. Thick Ge layers were then grown with a low temperature/high temperature approach on Ge nano-pillars and characterized by Atomic Force Microscopy, X-Ray Diffraction and cross-sectional Transmission Electron Microscopy. A degraded surface morphology, with otherwise similar structural properties was obtained for 2D Ge layers grown on Ge nano-pillars compared to growth on bulk Si. Defects such as stacking faults and twins also formed during the coalescence process.

Substitutional Carbon Incorporation in SiGeC/Si Heterostructures: Influence of Silicon Precursors

In this paper, SiGe or SiGeC epitaxy with Silane or Disilane, Germane and Methylsilane precursors was studied in a 300 mm industrial Reduced Pressure-Chemical Vapor Deposition (RP-CVD) reactor. The SiGe growth rate exponentially increased with the temperature in the 500 °C - 600 °C range for both silicon precursors (activation energy Ea = 2.1 eV). It was, at 550 °C, almost twice higher with Si2H6 than with SiH4. At low temperature, Si2H6 is indeed more reactive than SiH4, resulting in SiGe growth rates significantly higher for a given germanium composition. Then, carbon incorporation at 550 °C into Si0.8Ge0.2 was studied. The higher reactivity of Si2H6 compared to SiH4 resulted in a better substitutional carbon incorporation. In our experimental conditions, 1.2 at% of fully substitutional carbon atoms could indeed be obtained with Si2H6 (without any detectable interstitial ones). Meanwhile, only 0.5 at% of fully substitutional carbon atoms was obtained with SiH4.

Study on nano-graphitic carbon coating on Si mold insert for precision glass molding

Precision glass molding is an efficient and promising technique for large-volume micro-optical manufacturing. Even though significant progress in precision glass molding has been achieved on the anti-adhesive coating, technical challenges and barriers still exist towards tailoring the coating layer to ensure durability and long-term processing consistency in numerous molding cycles. This manuscript presents a novel molding technique utilizing micro-patterned Si mold inserts coated with a newly developed nano-graphitic carbon coating as an isolation layer in high-precision glass molding. The coating is prepared by atmospheric pressure chemical vapor deposition (APCVD), in which the liquid benzene and silicone rubber are used as the carbon source and silicon oxycarbide (SiOC) source, respectively. The nano-morphologies of the nano-graphitic carbon coating with different conditions are characterized and analyzed, illustrating notable differences in surface features with the addition of silicone rubber and various growth durations. In the demonstration, the nano-graphitic carbon-coated Si mold inserts exhibit unique properties, including anti-adhesive and hydrophobic at elevated temperatures. Two kinds of micro-patterned Si mold inserts, a micro-pillar matrix and a micro-lens array, generated by UV lithography and diamond turning, are utilized to demonstrate the feasibility of the anti-adhesive coating in precision glass molding. The obtained results indicate that the micro-optical features on the coated Si mold inserts are successfully transferred to glass substrates with high replication fidelity without notable signs of adhesion or contamination in repetitive molding cycles. This emerging technology makes Si an alternative mold material with low surface adhesion, enhances micro-optical machining efficiency, and replicates high-precision, low-cost micro-optics on large scales that were previously unavailable.

Decoupling trade-off thermoelectric relations and controlled out-plane lattice dynamics in few-layer MoS2

We report on the thermoelectric properties of few-layer MoS2 fabricated on 290 nm-SiO2/Si by a two-zone atmospheric pressure chemical vapor deposition (CVD) technique. The decoupling of electrical conductivity and Seebeck coefficient is noticed after 592 K, where the electrical conductivity (σ) is linearly increased and the Seebeck coefficient (S) is exponentially increased. The highest values of σ and S are 10.9 S cm−1 and 10312 nV K−1 at 734 K, respectively, and the highest power factor (S2σ) is 116 nW m−1 K−2 at 734 K. The calculated out-plane (A1g) displacement and the decreased A1g phonon lifetime are revealing the reduced phonon transport. The current investigations paved an attention to decouple the thermoelectric properties of few layer MoS2.

Cell and dendrite growth of tungsten by atmospheric pressure chemical vapor deposition

In this study, tungsten coatings are deposited at 300–610 °C from WF6 and H2 by atmospheric pressure chemical vapor deposition (APCVD). Tungsten powders adheres to the furnace walls (cold wall furnace) in every deposition, regardless of whether the coating is dense or not. These tungsten powders are proved to be produced by homogeneous reactions in gas phase near the substrate and adheres to the furnace inner wall as they move with the fluid. The presence of tungsten powders when depositing dense tungsten coatings indicates that the homogeneous reactions contribute to the growth of dense tungsten coatings; with this premise, the kinetics, structure and growth mode of tungsten coatings in APCVD system are discussed. Activation energy of 28.7 and 61.9 kJ/mol corresponded to rate-limiting steps of the diffusion of the tungsten atoms in gas phase, and the dissociation of H2. The<100>orientated columnar grains along the growth direction (GD) are main-branches. Not all but majority of the small grains intercalated between the columnar grains orient in the direction close to<111>along the GD, and these small grains are proved to be parts of second-branches. In the early stage of deposition, the<100>orientated grains compete with each other due to the growth of the cell tips in width. Raised areas are found on the surfaces of pyramids, and the microstructure of the growth interface shows that flat interface is prone to curved when there are more favorable growth conditions ahead. These results reveal that homogeneous reactions lead to the cell and dendrite growth mode of tungsten coatings in APCVD system.

Stabilized Synthesis of 2D Verbeekite: Monoclinic PdSe2 Crystals with High Mobility and In-Plane Optical and Electrical Anisotropy.

PdSe2 has a layered structure with an unusual, puckered Cairo pentagonal tiling. Its atomic bond configuration features planar 4-fold-coordinated Pd atoms and intralayer Se-Se bonds that enable polymorphic phases with distinct electronic and quantum properties, especially when atomically thin. PdSe2 is conventionally orthorhombic, and direct synthesis of its metastable polymorphic phases is still a challenge. Here, we report an ambient-pressure chemical vapor deposition approach to synthesize metastable monoclinic PdSe2. Monoclinic PdSe2 is shown to be synthesized selectively under Se-deficient conditions that induce Se vacancies. These defects are shown by first-principles density functional theory calculations to reduce the free energy of the metastable monoclinic phase, thereby stabilizing it during synthesis. The structure and composition of the monoclinic PdSe2 crystals are identified and characterized by scanning transmission electron microscopy imaging, convergent beam electron diffraction, and electron energy loss spectroscopy. Polarized Raman spectroscopy of the monoclinic PdSe2 flakes reveals their strong in-plane optical anisotropy. Electrical transport measurements show that the monoclinic PdSe2 exhibits n-type charge carrier conduction with electron mobilities up to ∼298 cm2 V-1 s-1 and a strong in-plane electron mobility anisotropy of ∼1.9. The defect-mediated growth pathway identified in this work is promising for phase-selective direct synthesis of other 2D transition metal dichalcogenides.

Atmospheric Pressure Chemical Vapour Deposition Growth of Graphene for the Synthesis of SiO2 based Graphene Ball

Graphene is a prominent carbon nanomaterial with fascinating characteristics such as high conductivity and very high charge carrier mobility at low temperatures. Numerous synthesis methods for graphene have been established. Chemical vapour deposition (CVD) is among the most successful methods to fabricate high-quality graphene. However, metal-catalyzed growth is used in virtually all of the CVD techniques mentioned. To remove these metal catalysts and relocate the graphene to the necessary dielectric substrate (SiO2/Si or quartz), complex and sophisticated post-growth methods must be used, which limits the usage of graphene in practical electronic components. In the present work, we conducted a preliminary study to determine the suitable methane(CH4) flowrate, which could be used to synthesise SiO2 based graphene ball. Few-layer graphene was grown on a large area of copper(Cu) surface using 20 sccm CH4 in atmospheric pressure CVD (APCVD). The influence of CH4 flowrate on graphene growth has been investigated. Graphene was deposited on a metal catalyst substrate at optimum temperatures of 1000 °C.

Impact of Thermally Reducing Temperature on Graphene Oxide Thin Films and Microsupercapacitor Performance.

In this work, a thermally reduced graphene oxide (TRGO) thin film on microscopic glass was prepared using spray coating and atmospheric pressure chemical vapour deposition. The structure of TRGO was analysed using X-ray diffraction (XRD) spectroscopy, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, and ultraviolet–visible spectroscopy (UV-Vis) suggesting a decrease in oxygen functional groups (OFGs), leading to the restacking, change in colour, and transparency of the graphene sheets. Raman spectrum deconvolution detailed the film’s parameters, such as the crystallite size, degree of defect, degree of amorphousness, and type of defect. The electrochemical performance of the microsupercapacitor (µ-SC) showed a rectangular cyclic voltammetry shape, which was maintained at a high scan rate, revealing phenomenal electric double-layer capacitor (EDLC) behaviour. The power law and Trasatti’s analysis indicated that low-temperature TRGO µ-SC is dominated by diffusion-controlled behaviour, while higher temperature TRGO µ-SC is dominated by surface-controlled behaviour.

Synthesis of WS2 by Chemical Vapor Deposition: Role of the Alumina Crucible

The role of the alumina crucible for the tungsten disulfide (WS2) growth on silicon dioxide substrates (SiO2/Si) under atmospheric pressure chemical vapor deposition (APCVD) was investigated. Both synthesis and properties of the APCVD-WS2 depend on the number of growth cycles when using the same alumina crucible. It was discovered that there is an ideal condition for the material’s synthesis, which is characterized by an increase in the photoluminescence (PL) yield and larger WS2 triangles. It usually happens for the first three growth cycles. For the fourth cycle and beyond, the PL decreases gradually. Simultaneously, atomic force microscopy images revealed no important changes in the topography of the WS2 flakes. As a function of the number of synthesis cycles, the progressive decrease in PL yield could be associated with materials with a higher density of defects, as identified by the LA(M)/A1g(M)−LA(M) ratio from Raman data using the green line.

Synthesis of SiC films by Atmospheric Pressure Chemical Vapor Deposition using Dimethylisopropylsilane Polymeric Precursor

Abstract: Silicon carbide (SiC) thin films were deposited on Quartz, SiC, and GaAs substrates under a hydrogen (H2) ambient at 850°C using dimethylisopropylsilane [CH(CH3)2SiH(CH3)2] as a single molecular polymeric precursor by the atmospheric pressure chemical vapor deposition (APCVD) technique. Effects on the SiC films from variation of precursor to H2 flow ratio in the reactive chamber as well as those which resulted when vacuum or positive pressures are utilized during temperature ramping have been investigated. Detailed analysis of Fourier Transform Infrared Spectroscopy (FTIR) results indicate the formation of SiC at 850°C in accordance with residual Si-CH2, Si-CH3 and Si-O bonds. Confirmed by either X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) or Energy Dispersive Spectroscopy (EDS), results show that the produced SiC films are dense, rough surfaced, void-free, and consist of a crystalline core showing the presence of beta-SiC and small amounts of alphaSiC. Pre-experimental thermodynamic modeling provided the valuable insight that an increase of the precursor to direct H2 flow ratio would provide a decrease of unreacted carbon in the SiC matrix yielding higher quality SiC films. These simulations also have shown reasonable agreement with our experimental observations. Keywords: SiC thin Film, Polymeric Precursor, Chemical Vapor Deposition, Thermodynamic Modelling

Low temperature thermally reduced graphene oxide directly on Ni-Foam using atmospheric pressure-chemical vapour deposition for high performance supercapacitor application

A binder free approach was use to prepare thermally reduced graphene oxide (TRGO) at 200 °C directly on Ni-Foam (NF) (current collector) via atmospheric pressure-chemical vapour deposition (AP-CVD) and used as a positive electrode for supercapacitor application. The TRGO/NF electrode preparation method is simpler, quicker, cheaper and more effective compared to other method. The half-cell electrochemical performances in 6 M KOH showed a maximum specific capacity of 52.64 mA h g−1 at 0.5 A g−1. The device: TRGO/NF//PAC showed a specific energy and power of 18.72 Wh kg−1 and 547.52 W kg−1 respectively at 1 A g−1; and 14.10 Wh kg−1 and 2.5 kW kg−1 respectively at 5 A g−1. The high coulombic efficiency (99.9%) and capacitance retention (70%) indicate outstanding stability. These results represent a significant progress in the fabrication of binder and conductive enhancement free positive electrode for electrochemical energy storage devices.

Strain-modulated optical response in 2D MoSe2 made by Na-assisted CVD on glass

Extended investigations on 2D transition metal dichalcogenides (TMDCs) have opened sound possibilities to apply these materials in several technological fields such as sensing. To this end, fully reproducible methods for the wafer-scale production of crystalline and uniform 2D TMDCs are in demand. In this work, atomically thin MoSe2 was grown by atmospheric-pressure chemical vapor deposition using the Na-assisted process with Se powder and Mo foil precursors on a glass substrate. The samples were extensively characterized via Raman and photoluminescence spectroscopy, atomic force microscopy, transmission electron microscopy, and x-ray photoelectron spectroscopy. The MoSe2 samples consist of submillimeter, monolayer single-crystals with 2H phase configuration. Being monolayer and crystalline, the samples exhibit well-defined and intense photoluminescence. CVD-grown 2D MoSe2 was integrated into a device with strain-tunable optical properties and tested. Under tensile strain (in the range of 0.2%–0.4%), the spectral emission responded to an in-plane strain with marked peak shifts toward lower energies for increasing levels of strain (∼3 and ∼2 nm shift for the main PL component at 0.2% and 0.4%, respectively), indicating a reduction of the bandgap.

Solar Cells with Laser Doped Boron Layers from Atmospheric Pressure Chemical Vapor Deposition

We present laser-doped interdigitated back contact (IBC) solar cells with efficiencies of 23% on an area of 244 cm2 metallized by a screen-printed silver paste. Local laser doping is especially suited for processing IBC cells where a multitude of pn-junctions and base contacts lay side by side. The one-sided deposition of boron-doped precursor layers by atmospheric pressure chemical vapor deposition (APCVD) is a cost-effective method for the production of IBC cells without masking processes. The properties of the laser-doped silicon strongly depend on the precursor’s purity, thickness, and the total amount of boron dopants. Variations of the precursor in terms of thickness and boron content, and of the laser pulse energy density, can help to tailor the doping and sheet resistance. With saturation-current densities of 70 fA/cm2 at sheet resistances of 60 Ohm/sq, we reached maximum efficiencies of 23% with a relatively simple, industrial process for bifacial IBC-cells, with 70% bifaciality measured on the module level. The APCVD-layers were deposited with an inline lab-type system and a metal transport belt and, therefore, may have been slightly contaminated, limiting the efficiencies when compared to thermal-diffused boron doping. The use of an industrial APCVD system with a quartz glass transport system would achieve even higher efficiencies.

Synthesis and Characterization of Boron Thin Films Using Chemical and Physical Vapor Depositions

Boron as thin film material is of relevance for use in modern micro- and nano-fabrication technology. In this research boron thin films are realized by a number of physical and chemical deposition methods, including magnetron sputtering, electron-beam evaporation, plasma enhanced chemical vapor deposition (CVD), thermal/non-plasma CVD, remote plasma CVD and atmospheric pressure CVD. Various physical, mechanical and chemical characteristics of these boron thin films are investigated, i.e., deposition rate, uniformity, roughness, stress, composition, defectivity and chemical resistance. Boron films realized by plasma enhanced chemical vapor deposition (PECVD) are found to be inert for conventional wet chemical etchants and have the lowest amount of defects, which makes this the best candidate to be integrated into the micro-fabrication processes. By varying the deposition parameters in the PECVD process, the influences of plasma power, pressure and precursor inflow on the deposition rate and intrinsic stress are further explored. Utilization of PECVD boron films as hard mask for wet etching is demonstrated by means of patterning followed by selective structuring of the silicon substrate, which shows that PECVD boron thin films can be successfully applied for micro-fabrication.

Controllable growth of large-area 1T′, 2H ultrathin MoTe2 films, and 1T′–2H in-plane homojunction

Atomically thin molybdenum ditelluride (MoTe2) has been intensively studied as an emerging material for electronics and optoelectronics due to its unique properties. While the small free energy difference between the 2H and 1T′ phases of MoTe2 always results in mixed-phase growth, precisely controlled phase transition of MoTe2 nanostructures is still a considerable challenge. Here, the centimeter-scale 1T′, 2H ultrathin MoTe2 films, and in-plane 1T′–2H homojunction have been synthesized by ambient pressure chemical vapor deposition based on the precursor design and space-confined strategies. The controllable growth of pure 1T′, 2H MoTe2, and 1T′–2H mixed-phase MoTe2 with phase separation and homogeneous mixture, respectively, has been achieved by adjusting growth temperature and growth time. The thickness of synthesized 1T′ and 2H ultrathin MoTe2 films can be effectively controlled by tuning the space-confined height. The corresponding growth mechanism was further illuminated based on systematically experimental characterizations and computational fluid dynamics simulations. The electrical transport properties of 1T′ and 2H MoTe2 films were investigated by conductive atomic force microscope and MoTe2-based thin-film field-effect transistors. Our experimental results provide a new route to realize the phase transition of two-dimensional materials, which makes these materials easily accessible as functional building blocks for next-generation electronic and optoelectronic devices.

Hexagonal Single-Crystal CoS Nanosheets: Controllable Synthesis and Tunable Oxygen Evolution Performance.

Cobalt-based sulfides with variable valence states and unique physical and chemical properties have shown great potential as oxygen evolution reaction (OER) catalysts for electrochemical water-splitting reactions. However, poor morphological characteristics and a small specific surface area limit its further application. Here, hexagonal single-crystal two-dimensional (2D) CoS nanosheets with different thicknesses are successfully prepared by an atmospheric-pressure chemical vapor deposition method. Because of the advantages of the 2D structure, more exposed catalytic active sites, better reactant adsorption ability, accelerated electron transfer, and enhanced electrical conductivities can be achieved from the thinnest 5 nm CoS nanosheets (CoS-5), significantly improving OER performance. The electrochemical tests manifest that CoS-5 show an overpotential of 290 mV at 10 mA cm-2 and a Tafel slope of 65.6 mV dec-1 in the OER in an alkaline solution, superior to those for other thicknesses of CoS, bulk CoS, and RuO2. For the mechanistic investigation, the lowest charge transfer resistance (Rct) and the highest double-layer capacitance (Cdl) were obtained for CoS-5, demonstrating the faster OER kinetics and the larger active area. Density functional theory calculations further reveal the enhanced density of states around the Fermi level and higher H2O molecule adsorption energy for thinner CoS nanosheets, promoting its intrinsic catalytic activity. Moreover, the two-electrode system with CoS-5 as the anode and Pt/C as the cathode requires only 1.56 V to attain 10 mA cm-2 in the overall water-splitting reaction. We believe that this study will provide a fresh view for thickness-dependent catalytic performance and offers a new material for the study of electronic and energy devices.