Nitride Nanowires Research Articles

Investigation of Electrical Behaviors Observed in Vertical GaN Nanowire Transistors Using Extended Landauer-Büttiker Formula

In this report, we study nonlinear electrical behaviors found in vertical-architecture transistors based on wrap-around-gated gallium nitride (GaN) nanowires (NWs) by extending a one-dimensional case of the Landauer-Buttiker formula. Here, the GaN NWs are considered “almost” one-dimensional ideal wires connecting the drain and source terminals, with the gate terminal serving to control the flowing current. Unlike previous models, which require several parameters and complex calculations, our proposed model only needs three parameters and simple calculations to match the experimental data. With this model, we confirm that the maximum current before saturation is a consequence of quasi-ballistic drain current. Thus, electron mobility has no effect in this device. Using a simple formulation, we discuss gating hysteresis in the device that is mediated by the selected oxide layer interface. We show that the memory effect of the device is attributed to time-delay current. The shorter gate length increases the transmission coefficient. As a result, the model can be employed to predict the next-generation NW transistor performance.

In Situ Integrated Co3W−WN Hybrid Nanostructure as an Efficient Bifunctional Electrocatalyst by Accelerating Water Dissociation and Enhancing Oxygen Evolution

AbstractDue to the difference of catalytic mechanisms, the design of an efficient alkaline bifunctional catalyst not only needs to organically integrate different active sites, but also has to simultaneously optimize the catalytic activity of both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Here, we propose a strategy of killing two birds with one stone to construct the efficient bifunctional electrocatalyst by simultaneously accelerating water dissociation and enhancing oxygen evolution. The self‐supported tungsten nitride nanowires decorated with tungsten cobalt alloy nanoparticles (Co3W/WN/CC) were synthesized on the flexible carbon cloth. Co3W can act as both a water dissociation promoter to enhance HER activity and OER active species to facilitate water oxidation via in situ transformation, thus effectively improving the overall water splitting performance. As expected, compared with pure tungsten nitride catalysts, the hybrid electrocatalyst not only shows enhanced HER activity with an overpotential decrease from 255 to 43 mV, but also achieves an excellent OER performance with overpotential of 273 mV in 1 M KOH aqueous solution. Furthermore, by employing Co3W/WN/CC as cathode and anode, the overall water splitting process needs 1.582 V to drive a current density of 10 mA cm−2 and maintains without decay for 80 hours. This work expands the effective strategy for building efficient, stable and low‐cost alkaline bifunctional electrocatalysts.

Highly Uniform, Self‐Assembled AlGaN Nanowires for Self‐Powered Solar‐Blind Photodetector with Fast‐Response Speed and High Responsivity

AbstractSearching for power‐independent, compact, and highly environment‐sensitive photodetectors is a critical step towards the realization of next‐generation energy‐efficient and sustainable integrated optoelectronic systems. Particularly, the deep ultraviolet (UV) band, which has large photon energy, is extremely suitable for environment monitoring and invisible light communication application. Herein, the demonstration of self‐powered deep UV solar‐blind photodetectors in a photoelectrochemical (PEC) cell configuration is reported, adopting wide bandgap n‐type aluminum gallium nitride (AlGaN) nanowires as photoelectrode. After decorating nanowires with noble metal ruthenium (Ru), the constructed solar‐blind PEC photodetectors exhibited excellent responsivity of 48.8 mA W‐1, fast response speed (rise time of 83 ms and decay time of 19 ms) with large photocurrent density of 55 μA cm‐2 at 254 nm illumination. Such superior performance can be attributed to, firstly and foremost, the successful synthesis of highly uniform and defect‐free n‐type AlGaN nanowires which ensures efficient photogeneration via effective light‐harvesting, and secondly, the boosted carrier separation and collection efficiency through Ru decoration. This novel nanoarchitecture enables deep UV photodetection to work stably with low energy consumption, intriguingly, opening the possibility for the development of high‐performance PEC photodetectors based on group III‐nitride semiconductors covering the entire spectral range from infrared to deep UV.

The Influence of Integrated Resistors Formed under Ion Irradiation on the Superconducting Transitions of Niobium Nitride Nanoconductors

The influence of integrated resistors formed under irradiation in a nanowire on its superconducting transitions has been investigated. Niobium nitride nanowires with widths of 75–20 000 nm fabricated from a 5-nm-thick NbN film on single-crystal silicon substrates coated with a 0.3-μm-thick thermal silicon oxide layer and on sapphire substrates have been considered. The influence of a built-in resistive region on the critical current of transition from the superconducting to normal state is described.

High responsivity GaN nanowire UVA photodetector synthesized by hydride vapor phase epitaxy

A gallium nitride (GaN) nanowire (NW) UVA photodetector with high responsivity was reported. The GaN NW was grown by horizontal hydride vapor phase epitaxy. The NW morphology is proved tunable via different growth conditions. The axial and radial growths of GaN NWs were investigated through vapor–liquid–solid and vapor–solid mixed growth models. Besides, NWs with different morphologies exhibit different growth crystal orientations, which depend on the flow rate of HCl. NWs with smaller diameters show better optical properties and crystalline quality. More importantly, the UVA detector fabricated by a single NW exhibits excellent responsivity of 4.35 × 104–1.06 × 105 A/W and external quantum efficiency of 1.48 × 107%–3.6 × 107% under different light power densities. The high responsivity and low production cost make the GaN NW UVA detector extremely attractive for several applications, such as fire sensing and missile and rocket warning.

Small-scale effects on the piezopotential properties of tapered gallium nitride nanowires: The synergy between surface and flexoelectric effects

Apart from the conventional wurtzite nanowires (NWs) with constant cross-sections, tapered wurtzite NWs with truncated conical shapes are also widely employed in the design of piezotronic nanodevices. In this paper, the piezopotential properties of tapered gallium nitride (GaN) NWs are comprehensively studied by using a multiscale modelling technique. Our atomic-scale simulations show that due to the surface effect, the material properties of tapered NWs strongly rely on the position in NWs. Analytic models based on the core-shell theory and the thermodynamic theory are developed for the position-dependent material properties of tapered NWs. Besides the surface effect, the flexoelectric effect is another factor significantly affecting the piezopotential properties of tapered NWs by inducing additional polarization. After employing the analytic models for position-dependent material properties and introducing a modified electromechanical theory, both the surface and flexoelectric effects are considered in the continuum mechanics modelling of the piezopotential of tapered NWs. Our results show that the small-scale effects can increase the potential difference generated in tapered NWs, which will become more significant as the tip radius decreases and the half cone angle increases. Moreover, in the tapered NW with a small half cone angle the small-scale effects are found to majorly originate from the surface effect, while the flexoelectric effect becomes the dominant factor when the tapered NW possesses a relatively large half cone angle.

Surface photovoltage spectroscopy observes junctions and carrier separation in gallium nitride nanowire arrays for overall water-splitting.

Gallium nitride (GaN) nanowire arrays on silicon are able to drive the overall water-splitting reaction with up to 3.3% solar-to-hydrogen efficiency. Photochemical charge separation is key to the operation of these devices, but details are difficult to observe experimentally because of the number of components and interfaces. Here, we use surface photovoltage spectroscopy to study charge transfer in i-, n-, and p-GaN nanowire arrays on n+-Si wafers in the presence and absence of Rh/Cr2O3 co-catalysts. The effect of the space charge layer and sub-bandgap defects on majority and minority carrier transport can be clearly observed, and estimates of the built-in potential of the junctions can be made. Transient illumination of the p-GaN/n+-Si junction generates up to -1.4 V surface photovoltage by carrier separation along the GaN nanowire axis. This process is central to the overall water-splitting function of the n+-Si/p-GaN/Rh/Cr2O3 nanowire array. These results improve our understanding of photochemical charge transfer and separation in group III-V semiconductor nanostructures for the conversion of solar energy into fuels.

Unraveling the photovoltaic properties of gallium nitride nanorods for solar water splitting

Researchers use surface photovoltage spectroscopy to measure junction properties in gallium nitride nanowire arrays

High performance solar-blind UV detector based on β-Ga2O3/GaN nanowires heterojunction

Gallium nitride nanowires and β-Ga2O3 nanowires were prepared by chemical vapor deposition. A solar-blind ultraviolet detector was fabricated based on β-Ga2O3/GaN nanowires heterojunction. The UV detector exhibits excellent response properties to deep ultraviolet with wavelength of 254 nm. The device exhibits a photo-to-dark current ratio of 1.375 × 103 and a high detectivity of 1.2 × 1011 Jones at 10 V bias Therefore, the responsivity of the UV detector is 27.5 mA/W under 254 nm ultraviolet light (8 mW/cm2) at 10 V bias voltage. The detector also has the advantages of easy preparation, low dark current, high rejection ratio, fast response, good stability and repeatability. The design method of β-Ga2O3/GaN nanowires heterojunction has the advantages of novelty and simplicity, which provides a new approach to fabricate a heterojunction detector.

N-doped carbon-embedded TiN nanowires as a multifunctional separator for Li–S batteries with enhanced rate capability and cycle stability

A 1D titanium nitride with an N-doped carbon composite was developed to suppress polysulfide shuttling and enhance the electrochemical reaction kinetics in Li-S batteries. Lithium-sulfur (Li–S) batteries have attracted considerable attention as next-generation energy storage devices owing to their high theoretical specific capacity and safety. However, the commercialization of Li–S batteries is hindered by critical issues, including the migration of the dissolved lithium polysulfides (LiPSs) from the sulfur electrode to the lithium metal anode, resulting in poor cycling stability. Here, we report a multifunctional interlayer configured with an N-doped carbon framework and titanium nitride nanowires on a polypropylene separator (NC/TiN NWs@PP) to suppress the polysulfide shuttling problem. NC/TiN NWs@PP can be obtained by electrospinning and the subsequent scalable solution-based vacuum filtration. The one-dimensional structure of the TiN NWs can shorten the Li-ion diffusion distance with large electrode/electrolyte interfaces. Furthermore, the N-doped carbon framework in the NWs enables facile electron transportation and allows the suppression of the shuttle effect to improve the electrochemical reaction kinetics. The Li–S battery with a NC/TiN NWs@PP separator exhibited enhanced cycling stability and rate capability, indicating that this could be a new research direction for Li–S batteries.

Manipulation of polarization characteristics in wurtzite ΙΙΙ-nitride nanowires for linearly polarized emission

Group ΙΙΙ nitrides are crucial semiconductors used in optoelectronic applications such as light-emitting diodes, but their efficiency is still limited due to some material problems including dislocations, strain, composition fluctuations and optical polarization properties. Nitride nanowire (NW) structures, showing advantages in these aspects, are a possible method to address the shortcomings of bulk materials and improve device performances. Here we investigated the manipulation of polarization characteristics in wurtzite ΙΙΙ-nitride NWs by controlling the diameter and strain using first-principles calculations. The inversion of valence bands between heavy/light hole and crystal-field split-off hole is induced with decreasing the diameter of AlN and InN NWs, which causes the switch of polarization characteristics from transverse-magnetic (TM) mode of bulk AlN (transverse-electric (TE) mode of bulk InN) to TE mode of small-diameter AlN NWs (TM mode of small-diameter InN NWs, i.e. linearly polarized emission). Moreover, we also obtained the linearly TM polarized emission in AlN and GaN NWs by applying the compressive strain along the NW axis. The physical origin of the polarization inversion is the variation of the structural parameter μ in NWs. Our results illuminate the polarization properties of wurtzite ΙΙΙ-nitride NWs and pave the way for their future optoelectronic devices.

GaN nanowires decorated with Pd for methane gas sensor

In this study, palladium (Pd)-decorated gallium nitride (GaN) nanowire have been prepared for room-temperature methane (CH4) gas sensors. The material was fabricated via MOCVD method combined with subsequent magnetron sputtering process and characterized by SEM technique. The SEM images indicate that the presence of different thickness of Pd film on the surface of the nanowires. When used for methane gas sensing, with the assistance of UV light, the 10nm Pd-decorated GaN nanowire sensor has the highest response to 200ppm methane, which were about 2 times higher than that of pure GaN samples. What’s more, 10nm Pd-decorated GaN sensor also has the lowest detection limit (20ppm) and the shortest response time (<10s). Thus, the application of Pd-GaN nanowire as methane gas sensor will have board prospects.

Decoupling Strategy for Enhanced Syngas Generation from Photoelectrochemical CO2 Reduction.

SummaryPhotoelectrochemical CO2 reduction into syngas (a mixture of CO and H2) provides a promising route to mitigate greenhouse gas emissions and store intermittent solar energy into value-added chemicals. Design of photoelectrode with high energy conversion efficiency and controllable syngas composition is of central importance but remains challenging. Herein, we report a decoupling strategy using dual cocatalysts to tackle the challenge based on joint computational and experimental investigations. Density functional theory calculations indicate the optimization of syngas generation using a combination of fundamentally distinctive catalytic sites. Experimentally, by integrating spatially separated dual cocatalysts of a CO-generating catalyst and a H2-generating catalyst with GaN nanowires on planar Si photocathode, we report a record high applied bias photon-to-current efficiency of 1.88% and controllable syngas products with tunable CO/H2 ratios (0–10) under one-sun illumination. Moreover, unassisted solar CO2 reduction with a solar-to-syngas efficiency of 0.63% is demonstrated in a tandem photoelectrochemical cell.

Freestanding vanadium nitride nanowire membrane as an efficient, carbon-free gas diffusion cathode for Li–CO2 batteries

A freestanding vanadium nitride nanowire (VN-NW) membrane is employed as a carbon-free gas diffusion cathode (GDC) for high-performance Li–CO2 batteries. Li–CO2 cells built with the VN-NW GDC exhibit excellent electrochemical performance, achieving 100 discharge/charge cycles with an ultralow round-trip overpotential of <1 ​V. The VN-NW GDC also delivers vastly improved capacity and rate capability compared to a conventional multiwalled carbon nanotube GDC. The morphology of the discharge products (Li2CO3 ​+ ​C) is greatly improved with the VN-NW GDC compared to the carbon-based cathode, allowing for facile decomposition on charge. Furthermore, the absence of carbon in the VN-NW GDC allows for easy characterization of the discharge products with a variety of techniques, including transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The impressive performance of the hierarchically structured VN-NW GDC in Li–CO2 batteries justifies further investigation into noble metal-free and carbon-free materials for gas diffusion cathodes.

Tunable Mechanical Property and Structural Transition of Silicon Nitride Nanowires Induced by Focused Ion Beam Irradiation.

Tailoring mechanical properties of the nanowire (NW) with intricate composite structure helps to design nanodevices with novel functionalities. Here, we performed in situ tensile deformation electron microscopy for the evaluation of the mechanical properties of the focused ion beam (FIB) irradiated silicon nitride (Si3N4) nanowires (NWs). Young's modulus of the FIB-fabricated NWs was mediated between the range of 522 and 65 GPa by modifying the shell thickness of the core-shell structure. The ion-beam-induced amorphization is found to induce the structural transition from an utter crystalline state to a composite NW with an amorphous shell, which results in a brittle-to-ductile transition and an unexpected plastic deformation. These results have practical implications for optimizing nanostructures with the desired mechanical properties, which are of fundamental relevance in designing and fabricating nanomechanical devices.

Fabrication of superconducting niobium nitride nanowire with high aspect ratio for X-ray photon detection

The niobium nitride (NbN) nanowires fabricated with the high-quality ultra-thin NbN film with a thickness of 3 nm–6 nm were widely used for single photon detectors. These nanowires had a low aspect ratio, less than 1:20. However, increasing the thickness and the aspect ratio of highly-uniformed NbN nanowires without reducing the superconductivity is crucial for the device in detecting high-energy photons. In this paper, a high-quality superconducting nanowire with aspect ratio of 1:1 was fabricated with optimized process, which produced a superconducting critical current of 550 μA and a hysteresis of 36 μA at 2.2 K. With the optimization of the electron beam lithography process of AR-P6200.13 and the adjustion of the chamber pressure, the discharge power, as well as the auxiliary gas in the process of reactive ion etching (RIE), the meandered NbN nanowire structure with the minimum width of 80 nm, the duty cycle of 1:1 and the depth of 100 nm were finally obtained on the silicon nitride substrate. Simultaneously, the sidewall of nanowire was vertical and smooth, and the corresponding depth-width ratio was more than 1:1. The fabricated NbN nanowire will be applied to the detection of soft X-ray photon emitted from pulsars with a sub-10 ps time resolution.

New direction's piezoelectricity and new applications of two-dimensional group V-IV-III-VI films: A theoretical study

Abstract It is challenging to realize the piezoelectricity of 2D films by exerting the stress along the direction perpendicular to the film plane. The ability to transfer the mechanical stress perpendicular to the films into electric energy can significantly enhance the transfer efficiency and have more broad application prospects, such as medical device (sphygmomanometer) and ultrathin nano-sensor devices (tactile sensor as the bionic skin of robot). Then the out-of-plane piezoelectric coefficients e33 and d33 of film have the special importance. We investigate the lattice and piezoelectricity properties of group V-IV-III-VI films (SnN–InO, GeN-GaO, and SiN–AlO) using first-principles calculations. It is found that they have the promising piezoelectric coefficients e33 and d33 due to their broken inversion symmetry along the direction perpendicular to the film plane. The e33 (38.69 × 10−10 C m−1) of SiN–AlO is the largest, which is larger than that (5.20 × 10−10 C m−1) of gallium nitride nanowires' surface layers by 7.4 times, while the out-of-plane piezoelectric strain coefficient d33 (5.29 × 103 pm V−1) of SnN–InO is the largest, which is one order of magnitude larger than that (0.42 × 103 pm V−1) of the Y-doped ZnO nano sheets. The special direction's piezoelectricity of the SiN–AlO and SnN–InO films indicates that they have the new applications in nanoscale energy harvesting devices, nano-sensor and other micro-electromechanical devices, which can transfer the mechanical stress perpendicular to the films into electric energy.

Electro-mechanical performance of smart piezoelectric nanocomposite plates reinforced by zinc oxide and gallium nitride nanowires

The use of piezoelectric nano-fillers in a non-piezoelectric matrix is a very attractive proposition for developing smart nanocomposite materials with desired electro-mechanical properties. The eco-friendly nanowires (NWs) of zinc oxide (ZnO) and gallium nitride (GaN) are the two candidates used to introduce smart piezoelectric nanocomposite materials. Specifically, in this first effort, we examined the electro-mechanical performance of newly developed composite plates reinforced by piezoelectric ZnO NW and GaN NW of varied volume fractions. The static deflections and natural frequencies of the newly developed bimorph piezoelectric nanocomposite plates subject to electro-mechanical loads are analyzed using a mesh-free method in conjunction with the shape functions of MLS. Using third order shear deformation theory (TDST), the coupled electro-mechanical governing equations for the considered smart plates are obtained and numerically integrated. The effects of the electro-mechanical loading and plate thickness on static deflection and natural frequencies of piezoelectric plates are investigated and discussed. Our predictions reveal that the application of electrical input to the plates can induce greater deflection than the ones introduced by mechanical loads and that ZnO NWs offer greater deflection than GaN NW. However, dynamic analysis indicates that GaN NW-reinforced plates have higher natural frequencies than those reinforced by ZnO NW.

Effective Growth of Pure Long-Straight Boron Nitride Nanowires Strain and Application as Flexible Humidity Sensor

Boron nitride nanowires (BNNWs) with high purity and a long-straight fashion are synthesized via ball milling and annealing technique at 1150°C successfully. These nanowires have an average length of more than $50\mu \text{m}$ with diameter 100 nm. The results of characterization showed that the main elements of the nanowires are boron and nitrogen, which molar ratio of B:N is close to 1 indicating the BN structure. The electrical properties of an individual BNNW were studied for the first time. The resistivity, carrier concentration, and carrier mobility of raw BNNWs were drawn from the experimental I-V curves. In addition, extremely stretchable BNNW networks two-terminal devices were fabricated on flexible and transparent elastomeric substrates. The electrical and mechanical properties of these devices were firstly investigated by bending tests. The as synthesized products were utilized as sensing material to detect strain and humidity. Results show that their electrical resistance increased with bending and humidity, proving the feasibility of the wearable human-friendly strain sensor and humidity sensing system. Our results indicate that BNNW networks are potential wearable sensor or medical integration of electronic implants.

Facile Synthesis and Optical Properties of Aluminum Nitride Nanowires Array.

AlN nanowires macro-array were successfully fabricated on Si substrate by double template method and chemical vapour deposition. The research shows that AlN nanowires array with different diameter, length and coverage can be prepared by controlling the experimental conditions. The as-prepared AlN nanowires array were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Furthermore, the Ultraviolet absorption of AlN nanowires array as a sensors was investigated and calculated with the first principle.