Carbon Doping Level Research Articles

Characterization of Trapping Effects Related to Carbon Doping Level in AlGaN Back-Barriers for AlGaN/GaN HEMTs

Characterization of Trapping Effects Related to Carbon Doping Level in AlGaN Back-Barriers for AlGaN/GaN HEMTs

Efficient charge carrier separation over carbon-rich graphitic carbon nitride for remarkably improved photocatalytic performance in emerging organic micropollutant degradation and H2 production

Graphitic carbon nitride (g-C3N4) shows great potentials in visible-light-driven catalytic oxidation of organic micropollutants to harmless products and reduction of water to H2 but suffers from drawback of sluggish charge carrier separation and transfer dynamics. To overcome this drawback, here a novel point defect engineering strategy, by a nicotinic acid or barbituric acid-assisted supramolecule self-assembly of dicyandiamide followed by thermal polymerization, is designed to prepare pyridine unit-incorporated g-C3N4 (CPyr-CNx) and carbon atom self-doped g-C3N4 (C-CNx). The strategy leads to well-regulated chemical structures of CPyr-CNx and C-CNx and thus the precisely controlled electronic structures. The CPyr-CNx and C-CNx both exhibit remarkably improved visible-light photocatalytic activity in degradation of emerging organic micropollutants (methylparaben, acetaminophen and bisphenol A) and water-splitting to H2 production in comparison of bulk g-C3N4 and carbon-rich g-C3N4 prepared by a direct thermal copolymerization of nicotinic acid or barbituric acid with dicyandiamide, and their photocatalytic redox activity depends on carbon doping level. Experimental results combined with theoretical simulations reveal that the superior photocatalytic redox performance of CPyr-CNx and C-CNx is mainly dominated by the significantly boosted charge carrier separation and transfer dynamics driven by carbon doping induced-local electric field and -midgap states, which finally generates abundant reactive oxidation species including •O2− anion radicals, •OH radicals and 1O2 for the deep oxidation of target organic micropollutants to significantly reduce their ecotoxicity; additionally, such efficient charge carrier separation and transfer also favors high mobility for free electron-involved photocatalytic H2 evolution reaction.

Aligned carbon-doping to modulate thermal and electrical conductivity of boron carbon nitride grown from chemical vapor deposition

Hexagonal boron carbon nitride (hBCN) thin films with a wide range of carbon doping are synthesized in a chemical vapor deposition (CVD) process by varying 3 distinct precursors. Utilizing the optothermal method, the highest thermal conductivities of hBCN thin films is measured experimentally as 836 ± 312 W/m·K, for the hBCN with the highest carbon doping, surpassing the measured hexagonal boron nitride (hBN) conductivity of 462 ± 158 W/m·K. Moreover, we demonstrate that the electrical conductivity retains the insulative properties of hBN with lower carbon doping levels. Additionally, insights of how increasing amounts of carbon increase the conductivity by forming graphene like channels integrated into the hBN networks have been examined by molecular dynamics simulations. These simulations confirm a greater increase in high frequency phonon group velocities contribute to higher thermal conductivity, when aligning carbon rather than simply increasing the quantity of carbon. The aligned carbon channels are effective in overcoming the additional phonon scattering, that occurs especially in the LA mode, when adding carbon to the hBN network. By varying the carbon doping to maximize the thermal conductivity while minimizing the electrical conductivity, we have discovered an effective method of producing optimized hBCN thin films, which are ideal to be utilized in thermal interface material applications as a lower cost alternative to hBN.

Controllable synthesis for carbon self-doping and structural defect co-modified g-C3N4: Enhanced photocatalytic oxidation performance and the mechanism insight

For the purpose of improving the photocatalytic performance of graphitic carbon nitride (g-C3N4) in the field of contaminant elimination, an in-situ malonamide-assisted strategy is provided to prepare carbon self-doping and structural defect co-modified g-C3N4 (CDCN) via preprocessing of the mixture of urea and malonamide followed by thermal copolymerization. Changing the initial malonamide dosage can precisely adjust the carbon doping level and structural defect concentration of CDCN. The characteristic results confirm that the doped C derived from malonamide was successfully implanted into the g-C3N4 framework by replacing sp2 hybrid N atoms (C−N=C) in the heptazine units, simultaneously forming some structural defects. Additionally, the preprocessing endows CDCN with good textural properties. So, the optimal CDCN20 shows remarkably enhanced visible-light photocatalytic activity in eliminating acetaminophen (APAP) and methylparaben (MPB) in water than pristine g-C3N4. By combining experimental and theoretical calculating results, the synergistic effect of C self-doping and structural defect promoting the photocatalytic performance of g-C3N4 is revealed thoroughly. This work provides a controllable strategy for synthesizing effective C self-doped g-C3N4 and a new insight into electronic structure and band structure-regulated photocatalytic oxidation mechanisms.

Precise carbon doping regulation of porous graphitic carbon nitride nanosheets enables elevated photocatalytic oxidation performance towards emerging organic pollutants

• Short carbon chain-incorporated g-C 3 N 4 are prepared by carbon atom-self doping route. • Visible-light harvesting ability and charge transfer dynamics of g-C 3 N 4 are promoted. • As-prepared HCN-C x show C doping level-dependent photocatalytic oxidation activity. • Abundant ROS such as •O 2 − , 1 O 2 and •OH are generated in HCN-C x photocatalytic system. • •OH and 1 O 2 are particularly important to elevated photocatalytic oxidation activity. To improve the photocatalytic oxidation performance of graphitic carbon nitride (g-C 3 N 4 ) towards organic pollutants, the present work develops a homogeneous carbon atom-self doping strategy to prepare porous carbon-rich g-C 3 N 4 nanosheets (HCN-C x ). The preparation process of HCN-C x includes preorganization of L-cysteine and urea under hydrothermal environment followed by thermal copolymerization, and carbon doping level can be precisely adjusted by changing initial urea/L-cysteine molar ratio from 5000, 1667, 1000 to 500. The characteristic results combined with theory calculations confirm that C C C skeleton from L-cysteine are introduced into the heptazine framework of g-C 3 N 4 by the replacement of some C N C units; additionally, the introduction of C C C skeleton can generate defect-induced midgap states in the band structure of g-C 3 N 4 . The HCN-C x nanosheets exhibit carbon doping level-dependent and notably elevated photocatalytic oxidation activity to three emerging organic pollutants including acetaminophen (APAP), levofloxacin (LEV) and methylparaben (MPB), in which the HCN-C 0.5 performs the best. After visible-light irradiation of the HCN-C 0.5 for 10, 8 and 90 min, the removal efficiency of APAP, LEV and MPB reaches up to nearly 100%. The excellent photocatalytic oxidation performance of HCN-C x is dominated by carbon atom-self doping, which can not only enhance the visible-light harvesting efficiency but also boost photoexcited charge carrier transfer dynamics. Consequently, abundant reactive oxygen species including •O 2 − , 1 O 2 and •OH are generated, and they are responsible for the elevated photocatalytic oxidation performance of HCN-C x .

Rational Control on Quantum Emitter Formation in Carbon-Doped Monolayer Hexagonal Boron Nitride.

Single-photon emitters (SPEs) in hexagonal boron nitride (hBN) are promising candidates for quantum light generation. Despite this, techniques to control the formation of hBN SPEs down to the monolayer limit are yet to be demonstrated. Recent experimental and theoretical investigations have suggested that the visible wavelength single-photon emitters in hBN originate from carbon-related defects. Here, we demonstrate a simple strategy for controlling SPE creation during the chemical vapor deposition growth of monolayer hBN via regulating surface carbon concentration. By increasing the surface carbon concentration during hBN growth, we observe increases in carbon doping levels by 2.4-fold for B-C bonds and 1.6-fold for N-C bonds. For the same samples, we observe an increase in the SPE density from 0.13 to 0.30 emitters/μm2. Our simple method enables the reliable creation of hBN SPEs in monolayer samples for the first time, opening the door to advanced two-dimensional (2D) quantum state engineering.

Fabrication of Black In2O3 with Dense Oxygen Vacancy through Dual Functional Carbon Doping for Enhancing Photothermal CO2 Hydrogenation

AbstractPhotothermocatalytic CO2 reduction as the channel of the energy and environmental issues resolution has captured persistent attention in recent years. In2O3 has been prompted to be a potential photothermal catalyst in this sector on account of its unique physicochemical properties. However, different from the metal‐based photothermal catalyst with the nature of efficient light‐to‐thermal conversion and H2 dissociation, the wide‐bandgap semiconductor needs to be modified to possess wide‐wavelength‐range absorption and the active surface. It remains a challenge to achieve the two aims simultaneously via a single material modulation approach. In this study, one strategy of carbon doping can empower In2O3 with two advantageous modifications. Carbon doping can reduce the formation energy of oxygen vacancy, which induces the generation of oxygen‐vacancy‐riched material. The introduction of oxygen defect levels and carbon doping levels in the bandgap of In2O3 significantly reduces this bandgap, which endows it full‐spectral and intensive solar light absorption. Therefore, the carbon doped In2O3 achieves effective light‐to‐thermal conversion and delivers a 123.6 mmol g–1 h–1 of CO generation rate with near‐unity selectivity, as well as prominent stability in photothermocatalytic CO2 reduction.

Molten salt synthesis of carbon-doped boron nitride nanosheets with enhanced adsorption performance

Owing to their large specific areas, high thermal stability and chemical inertness, two-dimensional boron carbon nitride nanosheets (BCNNs) have captured much attention in recent years in the field of adsorption of pollutants. The formation of BCNNs via incorporating carbon into boron nitride (BN) can effectively improve the photoelectric and adsorption properties of the latter. In this work, carbon-doped BN (BCN) nanosheets were prepared at 1100 °C via a molten salt route using boric acid, melamine and glucose as the main starting materials. The effects of molten salt type and carbon doping level on the formation of BCN were investigated, and their isothermal adsorption properties in a methylene blue (MB) aqueous solution were evaluated based on the Langmuir and Freundlich models. The results indicated that using molten LiCl-KCl as a liquid medium was more favorable than NaCl-KCl to the formation of BCNNs. As-prepared BC0.4N sample possessed a sheet-like structure of about 10 nm thick and a specific surface area as high as 484 m2 g−1. Moreover, the adsorption test of MB demonstrated a high adsorption capacity of 249.04 mg g−1, which was about 14 times higher than that in the case of the pristine BN, and the kinetic rate constant value in the case of using BC0.4N is about ten times as high as that of BN following a pseudo-second-order model, suggesting that the as-formed BC0.4N nanosheets could be potentially used as a value-added effective adsorbent for future wastewater remediation.

In-situ route for the graphitized carbon/TiO2 composite photocatalysts with enhanced removal efficiency to emerging phenolic pollutants

AbstractTiO2 is the most photoactive material because of its superstrong photooxidizing ability, and TiO2 photocatalysis has been widely applied in sustainable water treatment and environmental remediation. However, poor sunlight or visible-light harvesting efficiency and fast recombination rate of the photogenerated charge carriers severely limit the practical applications of TiO2. To overcome these problems, the present work demonstrates a facile in-situ co-condensation method combined with hydrothermal treatment to prepare a series of graphitized carbon/TiO2 composite photocatalysts, and anatase TiO2 phase and π-π-conjugated polycyclic aromatic carbon structure are created simultaneously. As-prepared TiO2/C composites exhibit remarkably high visible-light photocatalytic activity in the degradation of aqueous emerging phenolic pollutants, acetaminophen (APAP) and methylparaben (MPB), and apparent rate constant of the TiO2/C composite with carbon doping level of 10.3% for APAP and MPB removal is 7.6 and 2.8 times higher than that of bare TiO2, and 6.2 and 2.6 times higher than that of Degussa P25 TiO2. Based on the results of photoelectrochemical experiments, indirect chemical probe measurements, and ESR spectroscopy, it is verified that doping TiO2 with graphitized carbon is responsible for this enhanced photocatalytic activity, which renders the improved visible-light harvesting ability, the accelerated separation of the photogenerated charge carriers, and enlarged BET surface areas. Through analyzing the intermediates yielded in the photodegradation process, the pathway of visible-light photocatalytic degradation of APAP and MPB over the TiO2/C composite is proposed.

Effect of Ni doping on microstructure and superconductivity of MgB2 prepared by C - coated B powder

The MgB2 bulk doped with Ni nanoparticles with a composition of (Mg1.05B2)Nix (x = 0, 0.04, and 0.06) has been prepared by an in-situ method using the carbon-coated amorphous boron powder as precursor. The combination influence of Ni and carbon doping on the microstructure and superconductivity of MgB2 sample has been clarified according to the XRD, DSC, SEM and PPMS measurements. It is found that the carbon-coated boron in the present work has benefited to the uniformly refined MgB2 grains, as well as a high level of homogeneous carbon doping in the MgB2 samples. The increased grain boundaries and efficient carbon institution of B has significantly enhanced the Jc (High magnetic field) in the MgB2 bulks due to the more pinning centers compared to the normal amorphous boron precursor. Moreover, it has found that the irreversibility field (Hirr) of MgB2 is greatly improved. However, the positive effect of carbon coated boron has been weakened by Ni doping at low magnetic field. Meanwhile, the formed eutectic liquid by Ni and Mg at 506℃has promoted activity of the C replacement of the B site in MgB2, which distorted the MgB2 grains and worsened the intergranular connectivity.

Temperature Dependence of the Parameters of 1.55-μm Semiconductor Lasers with Thin Quantum Wells Based on Phosphorus-Free Heterostructures

InGaAs/InGaAlAs laser diodes operating in the 1.55-μm spectral range are studied. It is demonstrated that a certain level of carbon doping (1012 cm–2 per a single quantum well) allows one to reduce the temperature coefficient of variation of the lasing wavelength in such structures and raise the characteristic temperature of threshold current and differential efficiency at temperatures from 16 to ~50°C. These changes are accompanied by an increase in threshold current density and a reduction in differential efficiency.

Carbon doping of WS2 monolayers: Bandgap reduction and p-type doping transport.

Chemical doping constitutes an effective route to alter the electronic, chemical, and optical properties of two-dimensional transition metal dichalcogenides (2D-TMDs). We used a plasma-assisted method to introduce carbon-hydrogen (CH) units into WS2 monolayers. We found CH-groups to be the most stable dopant to introduce carbon into WS2, which led to a reduction of the optical bandgap from 1.98 to 1.83 eV, as revealed by photoluminescence spectroscopy. Aberration corrected high-resolution scanning transmission electron microscopy (AC-HRSTEM) observations in conjunction with first-principle calculations confirm that CH-groups incorporate into S vacancies within WS2. According to our electronic transport measurements, undoped WS2 exhibits a unipolar n-type conduction. Nevertheless, the CH-WS2 monolayers show the emergence of a p-branch and gradually become entirely p-type, as the carbon doping level increases. Therefore, CH-groups embedded into the WS2 lattice tailor its electronic and optical characteristics. This route could be used to dope other 2D-TMDs for more efficient electronic devices.

Изолирующие слои GaN, совместно легированные железом и углеродом

Surface morphology and conductivity properties of semiinsulating GaN epitaxial layers are studied. Improvement of insulating properties with carbon or iron doping level increase is limited by morphology deterioration. Morphology development is different for these two cases. Co-doping with carbon and iron allows keeping planarity with significant improvement of insulating properties.

Effect of Carbon Doping Level on Static and Dynamic Properties of AlGaN/GaN Heterostructures Grown on Silicon

The impact of the extrinsic carbon doping level was investigated with the aim of finding the optimal level for GaN-on-Si HFETs. A tradeoff between the crystal quality degradation by carbon doping and dynamic properties of HFET structures was observed indicating the role of vertical dislocations in the dynamic performance of the carbon-doped GaN buffer.

Energy-level dependent H2O2 production on metal-free, carbon-content tunable carbon nitride photocatalysts

Light-driven production of H2O2 from water and molecular oxygen could be a promising way for obtaining both solar fuels and fundamental chemicals. During that process, the H2O2 yield is strongly dependent on the reaction pathway associated with two-electron reduction of dioxygen by the photo-generated electrons. Herein, we synthesized a series of metal-free, carbon-content tunable carbon nitride photocatalysts (named C3N4Carbon) by a facile hydrothermal reaction and subsequent thermal treatment at appropriate temperatures. The energy levels of the C3N4Carbon catalysts vary with the carbon doping level, which is conveniently tuned by changing the initial glucose concentration during the hydrothermal reaction. The surface carbon species evolve with the carbon content and the nitrogen atoms in the structure of carbon nitride are partially substituted by foreign carbon atoms based on XPS measurements. The optimal catalyst leads to the highest H2O2 yield of 1271 µmol L−1 in an acidic aqueous solution (pH 3) after a reaction period of 4 h, twice higher than the pristine C3N4. In addition, the largest formation rate constant and the smallest decomposition rate constant of H2O2 are obtained on the optimal one according to the kinetics analyses. The decomposition tests of H2O2 indicate that the formation rate could be a dominant factor impacting the H2O2 yield. The conduction band position of the optimal catalyst is positively shifted to 0.06 V versus RHE, which is more favorable to the reduction of dioxygen to H2O2 (O2/H2O2 at 0.69 V versus RHE). The positive shift of valence band also improves hole collection and leads to enhanced formation of H2O2.

Experimental and Numerical Analysis of Hole Emission Process From Carbon-Related Traps in GaN Buffer Layers

The role of carbon-related traps in GaN-based ungated high-electron mobility transistor structures has been investigated both experimentally and by means of numerical simulations. A clear quantitative correlation between the experimental data and numerical simulations has been obtained. The observed current decrease in the tested structure during backgating measurements has been explained simply by means of a thermally activated hole-emission process with $E_{A} = 0.9$ eV, corresponding to the distance of the acceptor-like hole-trap level from the GaN valence band. Moreover, it has been demonstrated by means of electrical measurements and numerical simulations that only a low percentage of the nominal carbon doping levels induces the observed current reduction when negative substrate bias is applied to the tested structure.

Interrelation between magnetic and luminescent properties of aluminum oxide doped with copper and carbon

The results of researches of structural, luminescent and magnetic properties nanopowders (NPs) of pure and carbon (copper)-doped aluminum oxide, obtained by the pulsed electron beam evaporation are presented below. The suppression of the R-line ions Cr 3+ in photoluminescence spectra of all NPs is detected.All NPs without an exception (pure and doped) showed room temperature ferromagnetism. The nature of the observed ferromagnetism is connected with high concentration of the structural defects, which are formed in NPs in the course of their synthesis by means of pulsed electron beam evaporation in vacuum.The correlation between concentration of structural defects (oxygen vacancies) and ferromagnetic behavior of nanopowders is presented. The correlation was established between dependencies of the ratio integral intensity of the yellow and the red bands of photoluminescence spectra (the ratio integral intensity of the green and the red bands of pulsed cathodoluminescence spectra) and magnetization from carbon doping level.

Superior critical current density obtained in MgB2 bulks via employing carbon-coated boron and minor Cu addition

High performance Cu doped MgB2 bulks were prepared by an in-situ method with carbon-coated amorphous boron as precursor. It was found that the usage of carbon-coated boron in present work leads to the formation of uniformly refined MgB2 grains, as well as a high level of homogeneous carbon doping in the MgB2 samples, which significantly enhance the Jc in both Cu doped and undoped bulks compared to MgB2 bulks with normal amorphous boron precursor. Moreover, minor Cu can service as activator, and thus facilitates the growth of MgB2 grains and improves crystallinity and grain connectivity, which can bring about the excellent critical current density (Jc) at self fields and low fields (the best values are 7×105A/cm2 at self fields, and 1×105A/cm2 at 2T, 20K, respectively). Simultaneously, minor Cu addition can reduce the amount of MgO impurity significantly, also contributing to the improvement of Jc at low fields. Our work suggests that Cu-activated sintering combined with employment of carbon-coated amorphous boron as precursor could be a promising technique to produce practical MgB2 bulks or wires with excellent Jc on an industrial scale.

Investigation of breakdown properties in the carbon doped GaN by photoluminescence analysis

AbstractThe electrical and optical properties of the carbon doped GaN grown on Si substrate by metal‐organic chemical‐vapor deposition are investigated. Carbon impurity doping can improve the breakdown voltage effectively. However excess carbon in contrast depresses the breakdown voltage. This result is correlated with the carbon dopant behaviour in GaN which can be observed by analyzing the photoluminescence (PL) spectra. It is explained that the carbon impurity favours the formation of CN (carbon substitution of nitrogen) which acts as a deep level acceptor. The acceptor compensates the n‐type background impurities, which may resulting in suppressing the leakage current at high electric field, and leads to the improvement of the breakdown voltage. However, with excess carbon doping level, a significant amount of CGa (carbon substitution of gallium) form in GaN. The CGa, acting as the donor, compensates the CN and hence impairs the concentration of the deep level acceptor. In a result, the compensation of the n‐type background impurities by the deep level acceptor is curbed by the CGa‐CN self‐compensation effect, which leads to the decrease of the breakdown voltage. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Carbon Doping and Crystalline Quality on the Vertical Breakdown Characteristics of GaN Layers Grown on 200-mm Silicon Substrates

We have carried out a systematic study on the vertical breakdown behavior of GaN-based epitaxial layers on 200-mm-diameter Si(111) substrates with different carbon concentrations. The GaN layers were grown by metalorganic chemical vapor deposition by tuning growth parameters such as temperature and pressure. This study shows that, when the carbon concentration of the wafers is below 1 × 1018 cm−3, the vertical leakage currents are high with breakdown voltages below 260 V. The wafers that reveal lower vertical leakage currents are those with moderate carbon doping concentrations (between ∼1 × 1018 cm−3 and 2.5 × 1018 cm−3), whereas wafers with higher carbon concentrations (≥4 × 1018 cm−3) give rise to poor breakdown behavior caused by lower crystal quality and rougher surface morphology. The uniformity of vertical breakdown behavior across a 200-mm wafer shows that wafers with low crystal quality also exhibit poor uniformity. Moreover, when the carbon doping level is relatively high (between ∼2 × 1018 cm−3 and 2.5 × 1018 cm−3), good uniformity with variation of ∼5% can be achieved.