Pressure Chemical Vapor Deposition Method Research Articles

Synthesis of nitrogen and sulfur Co-doped carbon with special hollow sphere structure for enhanced catalytic oxidation

• Nano-CaCO 3 is used as template for carbon sphere synthesis by CVD. • The N and S doping percentage of the carbon sphere can be easily regulated. • The N and S co-doping can achieve enhanced activity than single doped carbons. • The incorporation of secondary S atoms could enhance the O 2 •− generation in the PMS activation. In this study, a facile atmospheric pressure chemical vapor deposition (CVD) method is used for the synthesis of nitrogen and sulfur co-doped hollow carbon sphere (NSC). Nano-CaCO 3 is used as template for the formation of hollow and highly hierarchical porous carbon structure. The doped percentages of N and S can be easily regulated by changing the ratio of N and S precursors and the deposition temperature. The obtained NSC is highly active for the catalytic oxidation of organic pollutants with peroxymonosulfate (PMS) as oxidant, and the reaction rate constant is 4.5 and 32.7 times faster than the single N or S doped samples, respectively. The PMS activation mechanism is comprehensively investigated by electron paramagnetic resonance (EPR) and radical quenching tests. Superoxide intermediate (O 2 •− ) and singlet oxygen ( 1 O 2 ) play the dominant role for phenol degradation. Moreover, with the introduction of secondary doped S atoms, more O 2 •− are generated for organics degradation. The excellent catalytic activity of NSC should be resulted from the optimized N and S doping percentages and large specific surface area (SSA). The synthesis strategy in this study provides a facile and low-cost synthetic method for heteroatom doped carbon materials and would expand the application of metal-free materials in the environmental remediation field.

Premade Nanoparticle Films for the Synthesis of Vertically Aligned Carbon Nanotubes

Carbon nanotubes (CNTs) offer unique properties that have the potential to address multiple issues in industry and material sciences. Although many synthesis methods have been developed, it remains difficult to control CNT characteristics. Here, with the goal of achieving such control, we report a bottom-up process for CNT synthesis in which monolayers of premade aluminum oxide (Al2O3) and iron oxide (Fe3O4) nanoparticles were anchored on a flat silicon oxide (SiO2) substrate. The nanoparticle dispersion and monolayer assembly of the oleic-acid-stabilized Al2O3 nanoparticles were achieved using 11-phosphonoundecanoic acid as a bifunctional linker, with the phosphonate group binding to the SiO2 substrate and the terminal carboxylate group binding to the nanoparticles. Subsequently, an Fe3O4 monolayer was formed over the Al2O3 layer using the same approach. The assembled Al2O3 and Fe3O4 nanoparticle monolayers acted as a catalyst support and catalyst, respectively, for the growth of vertically aligned CNTs. The CNTs were successfully synthesized using a conventional atmospheric pressure-chemical vapor deposition method with acetylene as the carbon precursor. Thus, these nanoparticle films provide a facile and inexpensive approach for producing homogenous CNTs.

Optimization and modeling of Zn2SnO4 sensitivity as gas sensor for detection benzene in the air by using the response surface methodology

In this paper, the performance of the benzene gas detection sensor in the air is optimized by an experimental design method. So in this work, Nanostructured thin films of ZnO and Zn2SnO4 were prepared in wurtzite form via a facile atmospheric pressure chemical vapor deposition (CVD) method, using metallic zinc and tin precursors. Characterization of the gas sensor was performed by using Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and surface area analysis (using BET method). The results show that Zn2SnO4 nanowire network exhibited good sensitivity at 299 °C temperature to low concentrations (100 ppb) of Benzene which can be potentially used as a resistive gas sensor. Ultimately modeling and optimization of Zn2SnO4 sensor performance to detect benzene by surface response method in design expert11 software has been done. Also, the effect of each parameter on the sensitivity of the sensor was analyzed by analysis of variance (ANOVA). Moreover, the performance efficiency of the Zn2SnO4 sensor is estimated with the reliable correlations obtained in the modeling. The two parameters selected to optimize the performance of the gas sensor include the operating temperature of the sensor and the concentration of the sensor. Comparison of the modeling results and the predicted values for the sensor sensitivity to benzene shows 97.60% excellent agreement.

Chemical Vapor Deposition of Superconducting FeTe1-xSex Nanosheets.

FeTe1-xSex, a promising layered material used to realize Majorana zero modes, has attracted enormous attention in recent years. Pulsed laser deposition (PLD) and molecular-beam epitaxy (MBE) are the routine growth methods used to prepare FeTe1-xSex thin films. However, both methods require high-vacuum conditions and polished crystalline substrates, which hinder the exploration of the topological superconductivity and related nanodevices of this material. Here we demonstrate the growth of the ultrathin FeTe1-xSex superconductor by a facile, atmospheric pressure chemical vapor deposition (CVD) method. The composition and thickness of the two-dimensional (2D) FeTe1-xSex nanosheets are well controlled by tuning the experimental conditions. The as-prepared FeTe0.8Se0.2 nanosheet exhibits an onset superconducting transition temperature of 12.4 K, proving its high quality. Our work offers an effective strategy for preparing the ultrathin FeTe1-xSex superconductor, which could become a promising platform for further study of the unconventional superconductivity in the FeTe1-xSex system.

Influence of Si doping on the microstructure and hardness of an AlTiSiN coating deposited by low pressure chemical vapor deposition

The effect of Si doping on the microstructure and hardness of an AlTiSiN coating deposited by the low pressure chemical vapor deposition (LPCVD) method was studied in detail using grazing incidence X-ray diffraction (GIXRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and a nanoindenter instrument. The results show that Al0.82Ti0.18N coating exhibits a typical columnar crystal structure, while Al0.88Ti0.09Si0.03N and Al0.82Ti0.08Si0.10N coatings show a fine equiaxed crystal structure. The number of internal substructures (dislocation, stacking fault, etc.) decreased, while the volume fraction of the amorphous structure increased with the increase of Si content. The results of GIXRD and HRTEM show that all AlTiSiN samples mainly consist of fcc AlN phase with a small amount of hcp AlN phase. Furthermore, a small amount of fcc TiN phase can only be observed in Al0.82Ti0.08Si0.10N coating. The hardness of Al0.82Ti0.18N, Al0.88Ti0.09Si0.03N, and Al0.82Ti0.08Si0.10N coatings is 33.0 ± 0.6 GPa, 38.3 ± 1.2 GPa and 27.0 ± 0.8 GPa, respectively. Al0.88Ti0.09Si0.03N coating has obvious potential value for industrial applications.

Self-intercalated two-dimensional magnetic semiconductor V8(S1-xSex)15

The exploration of two-dimensional (2D) magnets has attracted considerable attention due to their potential applications in spintronic devices over the past few years. Recently, a variety of 2D vanadium-based (V-based) chalcogenides have been demonstrated to own fascinating magnetic properties by both the theoretical predication and experimental realization. However, ternary V-based compounds have rarely been studied. Here, we synthesized three kinds of ultrathin ternary self-intercalated V8(S1-xSex)15 sheets with different Se contents by the atmospheric pressure chemical vapor deposition method. The Se content x is 8.7%, 12.1%, and 19.7%. The Raman spectra indicate that these three kinds of self-intercalated V8(S1-xSex)15 nanosheets with a different Se content own the same crystal structure. All self-intercalated V8(S1-xSex)15 nanosheets exhibit a semiconducting behavior, and the conducting type transits from ambipolar to p-type as the Se content increases. The spin Hall magnetoresistance (SMR) signal can be detected in the Pt/V8(S1-xSex)15 bilayer structure, and SMR signals (amplitudes) gradually weaken with the increasing temperature. These results manifest that self-intercalated V8(S1-xSex)15 own both semiconducting and magnetic characteristics.

Mechanistic investigation of aluminide coating formation by low-pressure chemical vapor deposition method on NiCoCrAlY coating in presence of nickel-ceria composite layer

In this study, a hybrid coating comprised of NiCoCrAlY fabricated by HVOF method, Ni–CeO2 composite coated by electrodeposition, and aluminide coating applied by low pressure chemical vapor deposition (LPCVD) method are investigated. To elucidate the formation process of aluminide coating, the microstructure and properties of the applied coatings were examined by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and EDS analyses. It was concluded that the desired β-NiAl phases are uniformly created within a single step on the surface. Furthermore, with the extending of the coating duration from 2 to 4 h, the thickness of the aluminide coating was increased from 14 to 25 μm. The thickness values were increased even further in the presence of Ni–CeO2 coating, where the growth mechanism was also changed. Within 4 h, a coating with a thickness of roughly 50 μm was obtained. Moreover, in the presence of Ni–CeO2 coating, it was observed that the inward diffusion of aluminum was predominant at the beginning of the process, whereas with longer processing durations, the outward diffusion of the nickel becomes dominant instead.

Enhanced Electrical Performance of Monolayer MoS2 with Rare Earth Element Sm Doping.

Rare earth (RE) element-doped two-dimensional (2D) transition metal dichalcogenides (TMDCs) with applications in luminescence and magnetics have received considerable attention in recent years. To date, the effect of RE element doping on the electronic properties of monolayer 2D-TMDCs remains unanswered due to challenges including the difficulty of achieving valid monolayer doping and introducing RE elements with distinct valence and atomic configurations. Herein, we report a unique strategy to grow the Sm-doped monolayer MoS2 film by using an atmospheric pressure chemical vapor deposition method with the substrate face down on top of the growth source. A stable monolayer triangular Sm-doped MoS2 was achieved. The threshold voltage of an Sm-doped MoS2-based field effect transistor (FET) moved from −12 to 0 V due to the p-type character impurity state introduced by Sm ions in monolayer MoS2. Additionally, the electrical performance of the monolayer MoS2-based FET was improved by RE element Sm doping, including a 500% increase of the on/off current ratio and a 40% increase of the FET’s mobility. The electronic property enhancement resulted from Sm doping MoS2, which led internal lattice strain and changes in Fermi energy levels. These findings provide a general approach to synthesize RE element-doped monolayer 2D-TMDCs and to enrich their applications in electrical devices.

Effect of annealing on the microstructure and mechanical properties of Ti0.17Al0.83N coating prepared by low pressure chemical vapor deposition

The face-centered-cubic (fcc) Ti 0.17 Al 0.83 N coating was deposited on cemented carbide insert by low pressure chemical vapor deposition (LPCVD) method. The effects of annealing temperature and atmosphere on the surface and fracture morphology, phase structure, residual stress, and hardness of the Ti 0.17 Al 0.83 N coating were studied. TEM analysis indicated that the as-deposited Ti 0.17 Al 0.83 N coating was self-organized with a periodically alternating Al-rich (9 nm) and Ti-rich (2 nm) nanolamellae. The width of the Al-rich (12 nm) and Ti-rich (3 nm) nanolamellae was increased after annealing in vacuum at 900 °C for 1 h. With the rise of vacuum annealing temperature from 700 to 1200°C, the coating hardness was increased and then decreased while the compressive residual stress was increasing continuously. A maximum hardness of 46.5 GPa was obtained after annealing in vacuum at 900 °C for 1 h. The coating grains cracked with the compressive residual stress of −1.55 GPa after annealing in vacuum at 1100 °C for 1 h. The surface morphology of the coating was basically unchanged after annealing in air at 900 °C for 1 h, while it was completely oxidized with the formation of Al 2 O 3 on the surface after annealing at 1000 °C. • Residual stress of CVD Ti 0.17 Al 0.83 N coating after vacuum annealing was analyzed. • The fraction of Al in Al- and Ti-rich nanolamellae layers are ~0.9 and ~0.6, respectively. • Coating structure before and after vacuum annealing was investigated by TEM analysis. • CVD Ti 0.17 Al 0.83 N hardness reached 46.5 GPa after vacuum annealing at 900 °C for 1 h.

Fabrication and Characterization of MoS2/h-BN and WS2/h-BN Heterostructures.

The general preparation method of large-area, continuous, uniform, and controllable vdW heterostructure materials is provided in this paper. To obtain the preparation of MoS2/h-BN and WS2/h-BN heterostructures, MoS2 and WS2 material are directly grown on the insulating h-BN substrate by atmospheric pressure chemical vapor deposition (APCVD) method, which does not require any intermediate transfer steps. The test characterization of MoS2/h-BN and WS2/h-BN vdW heterostructure materials can be accomplished by optical microscope, AFM, Raman and PL spectroscopy. The Raman peak signal of h-BN material is stronger when the h-BN film is thicker. Compared to the spectrum of MoS2 or WS2 material on SiO2/Si substrate, the Raman and PL spectrum peak positions of MoS2/h-BN heterostructure are blue-shifted, which is due to the presence of local strain, charged impurities and the vdW heterostructure interaction. Additionally, the PL spectrum of WS2 material shows the strong emission peak at 1.96 eV, while the full width half maximum (FWHM) is only 56 meV. The sharp emission peak indicates that WS2/h-BN heterostructure material has the high crystallinity and clean interface. In addition, the peak position and shape of IPM mode characteristic peak are not obvious, which can be explained by the Van der Waals interaction of WS2/h-BN heterostructure. From the above experimental results, the preparation method of heterostructure material is efficient and scalable, which can provide the important support for the subsequent application of TMDs/h-BN heterostructure in nanoelectronics and optoelectronics.

Origin of Mangetotransport Properties in APCVD Deposited Tin Oxide Thin Films.

Transparent conducting oxides (TCO) with high electrical conductivity and at the same time high transparency in the visible spectrum are an important class of materials widely used in many devices requiring a transparent contact such as light-emitting diodes, solar cells and display screens. Since the improvement of electrical conductivity usually leads to degradation of optical transparency, a fine-tuning sample preparation process and a better understanding of the correlation between structural and transport properties is necessary for optimizing the properties of TCO for use in such devices. Here we report a structural and magnetotransport study of tin oxide (SnO2), a well-known and commonly used TCO, prepared by a simple and relatively cheap Atmospheric Pressure Chemical Vapour Deposition (APCVD) method in the form of thin films deposited on soda-lime glass substrates. The thin films were deposited at two different temperatures (which were previously found to be close to optimum for our setup), 590 °C and 610 °C, and with (doped) or without (undoped) the addition of fluorine dopants. Scanning Electron Microscopy (SEM) and Grazing Incidence X-ray Diffraction (GIXRD) revealed the presence of inhomogeneity in the samples, on a bigger scale in form of grains (80–200 nm), and on a smaller scale in form of crystallites (10–25 nm). Charge carrier density and mobility extracted from DC resistivity and Hall effect measurements were in the ranges 1–3 × 1020 cm−3 and 10–20 cm2/Vs, which are typical values for SnO2 films, and show a negligible temperature dependence from room temperature down to −269 °C. Such behaviour is ascribed to grain boundary scattering, with the interior of the grains degenerately doped (i.e., the Fermi level is situated well above the conduction band minimum) and with negligible electrostatic barriers at the grain boundaries (due to high dopant concentration). The observed difference for factor 2 in mobility among the thin-film SnO2 samples most likely arises due to the difference in the preferred orientation of crystallites (texture coefficient).

Sensing Behaviour of V-doped 2D MoS2 in Sarin Detection

Although there are excellent properties in gas sensors, two-dimensional MoS2 (2D MoS2) has not been used in the detection of chemical agent sarin. In this paper, pure 2D MoS2 and V-doped 2D MoS2 sensors with few and multi-layers (5 and 10 layers, respectively) were prepared by low pressure chemical vapor deposition (LPCVD) method. The results of gas sensing tests show that V-MoS2(5 layers) exhibits the best sensing behavior in sarin detection. The low detection limit of V-MoS2(5 layers) (0.02 mg/m3) meets the requirements of on-site identification and detection of sarin agent at trace level.

Synthesis, Transfer, and Properties of Layered FeTe2 Nanocrystals.

Different from layered two-dimensional (2D) transition metal dichalcogenides (TMDs), iron dichalcogenides crystallize in the most common three-dimensional pyrite or marcasite structures. Layered iron dichalcogenides are rarely reported and little is known about their structures and properties. Here, layered hexagonal phase iron ditelluride FeTe2 (h-FeTe2) nanocrystals are grown on mica by atmospheric pressure chemical vapor deposition (APCVD) method and are fully characterized by various methods. Like other 2D layered TMD materials, the FeTe2 nanoflakes exhibit regular hexagon, half hexagon, or triangle shapes with a controllable thickness of 6-95 nm and lateral length from a few to tens of micrometers. A simple and effective method is used to transfer the FeTe2 nanoflakes from the mica substrate onto any other substrates without quality deterioration by using polystyrene (PS) as a support polymer, which can also be operated in ethanol or ethylene glycol in a glovebox to avoid contact with water and air. Temperature-dependent electrical transport demonstrates that the FeTe2 nanoflake is a semiconductor with a variable range hopping (VRH) conduction, and its nonsaturated linear magnetoresistance (MR) reaches up to 10.4% under magnetic field of 9 T at 2 K, both probably due to its structure disorders. No signature of magnetic ordering is observed down to 2 K. The CVD growth of this layered FeTe2 represents an addition to the extensive library of 2D materials, particularly iron chalcogenides or alloys. Synthesis, properties, and even doping of phase pure h-FeTe2 call for further study in the future.

Chromium doped zinc selenide optical fiber lasers

The optical fiber geometry is known for rugged, high power laser sources that are preferred for many applications, but is typically limited to the visible and near-infrared regions of the electromagnetic spectrum due to the transmission limits of silica (< 2 µm). This wavelength range could be extended into the mid-infrared using transition metal doped, crystalline II-VI optical gain media, but these materials cannot be fabricated into optical fibers using conventional glass drawing methods. An in-situ high pressure chemical vapor deposition method for the fabrication of silica-cladded ZnSe fiber cores uniformly doped with Cr 2 + is reported. Optical pumping experiments reveal that these doped fibers exhibit threshold behavior and thus function as mid-infrared optical fiber lasers. Finite element calculations show that undesirable thermal effects common in bulk II-VI crystals are mitigated in the fiber geometry.

3D graphene/fly ash waste material for hybrid supercapacitor electrode: specific capacitance analysis

AbstractThe performance of supercapacitor energy storage is depending on the type of the material that is used as supercapacitor electrode. Graphene has been widely used as the base material for a lot of applications due to its remarkable properties. In this research, we try to combine 3D Graphene with waste material fly ash to be used as the electrode of supercapacitor. Fly ash is a residual material from burning pulverized coal in electric generation power plants which contain metal oxide materials such as iron oxide and aluminum oxide. This residual material might be usable as an electrode for supercapacitor due to its material contained. As the base material, the 3D graphene was successfully fabricated by using low pressure chemical vapor deposition (LPCVD) method and afterwards the fly ash was coated on the top of 3D graphene. The chemical properties and surface structure of the electrode material was studied by using Raman spectroscopy and field emission scanning electron spectroscopy (FESEM). 3 electrode systems were used to analyze the cyclic voltammetry results. According to the results, they show that the highest specific capacitance of 3D graphene/fly ash (FA) was about 0.025 F/cm2 at the lowest scan rate of 5 mV/s and it is recommended to use as the supercapacitor electrode.

Mg0.35Zn0.65O/Al/ZnO Photodetectors With Capability of Identifying Ultraviolet-A/Ultraviolet-B

This article proposes an Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.35</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.65</sub> O/Al/ZnO structure, with which photodetectors (PDs) are able to identify ultraviolet (UV)-A (400-320 nm) and UV-B (320-280 nm). Both Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.35</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.65</sub> O and ZnO thin films are deposited using mist atmospheric pressure chemical vapor deposition (MAPCVD) method. At first, the material characteristics such as crystal structure, oxygen deficiency, energy bandgap, and photoluminescence (PL) of Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.35</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.65</sub> O and ZnO thin films are analyzed. The present Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.35</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.65</sub> O/Al/ZnO PD shows UV-B to UV-A rejection ratio of 15 in the spectral responsivity characteristics. Additionally, the detectivity characteristics suggest that the present Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.35</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.65</sub> O/Al/ZnO PD is able to identify UV-A and UV-B. Furthermore, the Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.35</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.65</sub> O/ZnO hetero-interface enhances the carrier mobility which further improves the response time.

Synthesis of High-Quality Multilayer Hexagonal Boron Nitride Films on Au Foils for Ultrahigh Rejection Ratio Solar-Blind Photodetection.

Solar-blind photodetectors have widespread applications due to the unique merit of a "black background" on the earth. However, most solar-blind photodetectors reported previously exhibited quite low rejection ratios (R200nm/R280nm < 103) and were interfered with by light longer than 280 nm. Herein, by an ambient pressure chemical vapor deposition (CVD) method, large-area, clean, and uniform two-dimensional (2D) multilayer h-BN films with different thicknesses have been successfully synthesized on Au foils. The synthesized multilayer h-BN film is transparent to light longer than 280 nm, showing excellent optical and optoelectronic properties to weak solar-blind light (μW/cm2). This sensitive solar-blind h-BN photodetector exhibits ultrahigh rejection ratios (R220nm/R280nm > 103 and R220nm/R290nm > 104), a low dark current (102 fA), and a large detectivity (3.9 × 1010 Jones). It is noteworthy that the rejection ratio (R220nm/R290nm) here is superior to most of those previously reported based on traditional semiconductors. This large-scale, clean, and uniform multilayer h-BN film will contribute to the progress of next-generation optoelectronic devices.

Fluid-Guided CVD Growth for Large-Scale Monolayer Two-Dimensional Materials.

Atmospheric pressure chemical vapor deposition (APCVD) has been used extensively for synthesizing two-dimensional (2D) materials because of its low cost and promise for high-quality monolayer crystal synthesis. However, the understanding of the reaction mechanism and the key parameters affecting the APCVD processes is still in its embryonic stage. Hence, the scalability of the APCVD method in achieving large-scale continuous film remains very poor. Here, we use MoSe2 as a model system and present a fluid guided growth strategy for understanding and controlling the growth of 2D materials. Through the integration of experiment and computational fluid dynamics (CFD) analysis in the full-reactor scale, we identified three key parameters, precursor mixing, fluid velocity, and shear stress, which play a critical role in the APCVD process. By modifying the geometry of the growth setup to enhance precursor mixing and decrease nearby velocity shear rate and adjusting flow direction, we have successfully obtained inch-scale monolayer MoSe2. This unprecedented success of achieving scalable 2D materials through fluidic design lays the foundation for designing new CVD systems to achieve the scalable synthesis of nanomaterials.

Surface Current Improvement of Magnesium-Doped Hexagonal Boron Nitride Monolayer by Additional Nitrogen Gas Flow

Abstract Hexagonal boron nitride (h-BN) is the most well-known wide band gap two-dimensional (2D) material (&amp;gt; 6 eV). To achieve its applications in optoelectronic devices, the conductance of h-BN must be implemented to the extent that it can be fabricated into a p–n junction. Here, we demonstrate a method to improve the surface current of p-type h-BN monolayer by introducing additional nitrogen gas flow during growth. First-principles calculations were conducted to show that nitrogen atmosphere can promote the formation of boron vacancy, making a low barrier site for Mg doping incorporation. Magnesium-doped h-BN monolayer was achieved using a low pressure chemical vapor deposition method under N2 flux. The surface current has been enhanced by three times up to 16 μA under 4 V external voltage. This approach provides potential applications of controllable conductive h-BN film for two-dimensional optoelectronic devices.

Development of ultra-thin doped poly-Si via LPCVD and ex-situ tube diffusion for passivated contact solar cell applications

Rear side application of polycrystalline silicon (poly-Si) passivated contacts has demonstrated very high efficiencies for single-junction monocrystalline silicon (mono-Si) solar cells. To further improve the device performance, one possible approach is to apply the passivated contact concept to the front side of the solar cell as well. The front side application requires the use of ultra-thin poly-Si layer in order to suppress parasitic absorption. Suitable ex-situ diffusion process should be developed accordingly without damaging the passivation provided by the very thin interface oxide (iOx). In this work, we prepared symmetric lifetime samples of ultra-thin poly-Si (<30 nm) via low pressure chemical vapour deposition (LPCVD) method. Then we studied and optimised the ex-situ POCl3/BBr3 diffusion doping processes. An excellent passivation quality was demonstrated with a high implied open-circuit voltage (iVoc) of up to 730 mV (on symmetric n+ poly-Si lifetime samples) and 700 mV (on symmetric p+ poly-Si lifetime samples). For possible contact formation, we capped the poly-Si with sputter-deposited ZnO:Al, which shows good opto-electrical properties and firing stability at 650 °C.