P-type NiO Research Articles

P-type semi-transparent conductive NiO films with high deposition rate produced by superimposed high power impulse magnetron sputtering

High power impulse magnetron sputtering (HiPIMS) technology with extremely high target ionization rate is employed to deposit Ni3+-rich NiO films with enhanced p-type conductivity. However, the HiPIMS technique possesses a significant disadvantage; that is, its low deposition rate. In order to overcome this drawback, superimposed HiPIMS ( HiPIMS+MF) power supply was employed in this work. The influence of the MF pulse duration on the films’ composition, morphology, chemical status, structure and optoelectronic properties is investigated here. The results show that compared with pure HiPIMS deposition, the deposition rate of superimposed HiPIMS technology is significantly improved. Meanwhile, the advantages of HiPIMS with high ionization rates are retained. Ni3+-rich NiO films are produced using superimposed HiPIMS deposition. Especially in HiPIMS+MF 3X deposition mode, a relatively low resistivity of 3.41 Ω cm with high deposition rate (2.32 Å/s) is realized.

Si-embedded metal oxide transparent solar cells

Abstract Transparent photovoltaic (TPV) is the technology of solar cells to convert light to electric energy. Different from the typically dark or opaque solar cells, TPV is transparent by passing the visible range lights. Metal-oxide semiconductor TPV was developed for short ultraviolet (UV) utilization. The solid-phase sputtering method was applied to sequentially deposit p-type NiO onto n-type ZnO forming the electric field. The pristine metal-oxide TPV has strong absorption of UV but bears the inevitable limit of carrier collection. Extension of light-utilization is a pivot to enhance TPV performances. And thus, a thin Si film was embedded between p-NiO and n-ZnO to improve TPV performances according to the enhanced quantum efficiency as well as the extended absorbing light. The Si-embedded TPV has 40% transmittance to achieve the large open circuit voltage (0.6 V) and short circuit current density (2.8 mA/cm2) values for high light-conversion efficiency of 4.8%. This may be the first report for the hybrid of Si-embedded metal-oxide heterojunction for TPVs. Si film would enhance the metal-oxide TPV performances due to the improved carrier collection efficiency and the extended light utilization for longer wavelengths. The inorganic TPV may be applied for the invisible power generator.

Hierarchical NiO–CeO nanosheets self-assembly flower-like architecture: heterojunction engineering assisting for high-performance humidity sensor

Due to its high performance, good sensitivity, fast response and recovery time, p-n heterojunction layer-like nanostructure consisting of two kinds of semiconducting metal oxide materials can be regarded as one of the most promising sensor materials for humidity detection at room temperature. In this study, NiO–CeO p-n heterojunction-based 2D nanosheet self-assembled architectures have been developed for constructing high-performance humidity sensors. Morphology and structure characterizations reveal that the novel heterostructures are composed of 3D flower-like porous microspheres self-assembled by 2D layered nanosheets with high surface area and abundant active sites, in which the amorphous n-type CeO nanocrystalline with only several nanometers homogeneously distributes into the p-type NiO nanosheet matrix. The sensors presented excellent humidity sensing performance with high sensitivity and a pseudo-linear response to water gas in the relative wide humidity (RH) range of 11–95% at room temperature with excellent stability, reproducibility and fast response speed. These improved properties can be greatly attributed to the unique 3D flower-like architectures with a large specific surface area and the NiO–CeO heterojunction interface and synergistic effect. Such a high performances of NiO–CeO p-n heterojunction humidity sensor can have great potential applications in highly sensitive humidity sensors.

1D hierarchical CdS NPs/NiO NFs heterostructures with enhanced photocatalytic activity under visible light irradiation

One-dimensional (1D) hierarchically structured CdS nanoparticles (NPs)/NiO nanofibers (NFs) heterostructures with remarkable removal efficiency for diazo dye Congo red (CR) were fabricated by a stepwise synthesis process, which was involved a chemical bathing deposition combined with calcination, and a microwave-assisted wet chemical reaction. The crystal phases, morphologies, optical absorption properties, and adsorption/photocatalytic activity of as-prepared products were investigated by XRD, FESEM, TEM, high-resolution TEM (HRTEM), N2 adsorption/desorption isotherms, UV–Vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectrum respectively. The experimental results indicated that binary satellite- core CdS NPs/NiO NFs heterojunctions are comprised of n-type CdS NPs with size of 10–30 nm decorated onto 1D p-type NiO NFs with diameter of 60–180 nm and length up to microns, which are self-assembled by nanoparticles with 30–100 nm in size. The possible formation mechanism for satellite-core structured CdS/NiO heterojunction is proposed. Interestingly, the decolorization efficiency over CdS/NiO heterostructures reached up to 91.2% in removal of aqueous CR at high concentration within 40 min under visible light irradiation, which was approximately 5.2 and 3.8 times as high as that of pure CdS nanocrystals (NCs) and the mixture of NiO NFs and CdS NCs. Furthermore, the possible photocatalytic mechanism was also investigated. The as-designed hybrid CdS NPs/NiO NFs heterostructures exhibited improved photocatalytic activity, which is attributed to the enhancement of the visible light adsorption, the efficient separation of photogenerated electrons and holes, and the high adsorption capacity towards CR molecules, thereby displaying superior visible- light-driven photodegradation of CR in high concentration. This work may provide a green engineering heterojunction technology to develop the advanced multifunctional nanocomposites for their applications in wastewater purification.

Sc-doped NiO nanoflowers sensor with rich oxygen vacancy defects for enhancing VOCs sensing performances

Identifying the defect type which closely correlates with gas/metal oxide semiconductor (MOS) interfacial charge exchange is of utmost importance for rationally designing high performance MOS gas sensors, which are essential for the emerging sensing electronics for assessing the personal health and environment pollution. Herein, we report the sensing performance of p-type NiO toward volatile organic compounds (VOCs) molecules could be drastically improved by Sc dopant. At an optimal doping ratio of 7.4 at.%, the sensor response to 100 ppm acetone was boosted from 8.2 (pure NiO) to 109.4, with a low detection limit of 10 ppb. Comprehensive defect characterizations indicate surface unsaturated oxygen vacancy (VO) defects act as active sites that facilitate the interfacial charge exchange at elevated temperatures. Our work highlights that abundant VO defects induced by aliovalent Sc dopant play an important role in boosting the sensitivity of p-type NiO toward VOCs, and provide valuable guidance in designing high performance p-type MOS sensors.

Fundamental Triangular Interaction of Electron Trajectory Deviation and P-N Junction to Promote Redox Reactions for the High-Energy-Density Electrode.

Highly efficient redox reaction of active electrode materials is the guarantee for achieving high energy density for energy storage devices. Here, we design a triangle of the electrode material involving the P-N junction between NiO (p-type) and MoO3 (n-type) and electron trajectory deviation between gold nanoparticles with NiO or MoO3. This optimized fundamental triangle structure could facilitate the redox reaction of a metal oxide, and thus the fabricated ternary nanocomposites exhibit excellent electrochemical performance. At a lower current density (0.5 A g-1), the mass specific capacitance of a single electrode can reach 943.3 F g-1, while the NiO/MoO3 tested under the same conditions only has a specific capacitance of 278.9 F g-1. The assembled asymmetric device with activated carbon shows a higher capacitance retention rate of 98.7% after long-term cycling under different current densities, and a maximum energy density of 28.9 W h kg-1 (power density of 400.1 W kg-1). The crucial prerequisite of this strategy is the lower work function of gold nanoparticles compared with active materials, which significantly reduce the activation energy of NiO/MoO3 and the formed P-N junction between p-type NiO with n-type MoO3 in their contact interfaces. This novel design of a triangle structure could be expected to be applied in other materials to develop a kind of energy storage device with excellent electrochemical performance.

Fabrication of a propanol gas sensor using p-type nickel oxide nanostructures: The effect of ramping rate towards luminescence and gas sensing characteristics

We report on the effect of the annealing temperature ramping rate on the gas sensing performance towards n-propanol gas and the luminescence properties using p-type NiO gas sensors prepared by the hydrothermal method and annealed at various ramping rates. The crystallite sizes of NiO nanostructures decreased from 22 to 7.4 nm, while the Brunauer–Emmett–Teller measurements complemented that by showing improvement in surface area from 0.15 to 129.11 m2/g. The blue emission observed from photoluminescence studies was associated with oxygen and/or nickel vacancies. The existence of a non-stoichiometric NiO was thoroughly investigated by x-ray photoelectron spectroscopy. Among the fabricated p-type NiO sensors, the ramping rate of 1 °C/min NiO-based sensor demonstrated excellent sensitivity, rapid response/recovery times and low limit of detection to n-propanol in dry air and relative humidity (RH) conditions. Moreover, NiO-1 oC/min-based sensor showed enhanced and stable response in the existence of various RH and its response remained stable with RH percentage. Such stability to RH changes makes it competitive for practical applications. The sensor further showed a clear stability towards n-propanol after 10 days, proving that it can be considered as a possible contender for the detection of n-propanol gas at relatively low operating temperatures.

Dark current analysis of p-i-n NiO/BiTiO3/ZnO thin film heterojunction diode

Dark current analysis of fabricated NiO/BiTiO3/ZnO heterojunction thin film p-i-n diode is demonstrated in this paper. The diodes layers; p-type NiO, i-type BiTiO3 and n-type ZnO were fabricated by using a sol-gel method on glass substrates. This method is the most practical techniques used for manufacturing the nanostructured thin films of metal oxide and perovskite semiconductors. The electrical characteristics of the vertical p-i-n diode were investigated using current-voltage characterization at room ambient in dark condition. The parameters, for example, threshold voltage, rectifying ratio, ideality factor, junction resistance and leakage current, were extracted from the measured data. The turn on voltage, ideality factor, saturation current, junction series resistance, and junction shunt resistance were estimated to be 0.6 V, 6.1, 8×10-7 A, 40 Ω and 760 Ω, respectively. The effect of post-fabrication heat treatments on electrical properties has been studied. The optimum temperature at 100°C that improves the device performance. The performance enhancement attributed to the interface improvement of the between the aluminum contact and p-i-n thin films. With respect as-deposited p-i-n devices, the heat-treated diodes performance parameters such as threshold voltage, ideality factor and leakage current of devices are found to improve by 5%, 47.3%, and 63.3%, respectively. The rectification performance of the device was 13.6 at 100°C and degrades after the temperature reached 125°C attributed to new material phases appears at interfaces.

Epitaxial Growth of Bendable Cubic NiO and In2O3 Thin Films on Synthetic Mica for p- and n-type Wide-Bandgap Semiconductor Oxides

AbstractBendable p-type NiO and n-type In2O3 thin films were epitaxially grown on synthetic mica using mist chemical vapor deposition. It was found that at a growth temperature of 400 °C, epitaxially grown cubic (111) NiO thin films developed twin rotational domains, and the epitaxial relationship between each domain and the substrate was (111) NiO [1-10] or [10-1] || (001) synthetic mica [100]. In the visible light region, the epitaxial NiO thin films showed high transparencies, and their cut-offs appeared in the UV region. Additionally, at a growth temperature of 500 °C, cubic (111) In2O3 thin films with and without Sn doping were epitaxially grown on synthetic mica. As a result of the plasma oscillation of free carriers, Sn-doped In2O3 thin films exhibited reflection characteristics in the infrared region, while maintaining their visible light transmission characteristics. Furthermore, compared with non-doped In2O3, Sn doping decreased the sheet resistance by two digits.

Acetone Sensing Properties of NiO Nanofibers Based on Electrospinning

Acetone is a main respiratory marker for diabetic patients. In this paper, P-type NiO nanofibers were prepared by electrospinning and used for the detection of acetone gas. NiO nanofibers were characterized by SEM and XRD. The uniform NiO nanofibers with face-centered cubic structure was obtained. The working temperature of NiO nanofibers was optimized, and the optimal operating temperature is 220°C. The response-recovery curve was tested, and the response and recovery time is 24.6 s and 610 s respectively. The response to different concentrations of acetone was also analyzed, and the detection limit was 100 ppb. These results show that NiO nanofibers based on electrospinning have potential applications in the respiratory testing of diabetes.

UV Photodetector Based on p-NiO film/n-Si Heterojunction Prepared by Thermal Oxidation

In this work, p-type NiO film was grown on n-type Si substrate as UV photodetector. NiO film was prepared over n-type Si (100) through two-step method. First, metallic Ni film was deposited on Si wafer using thermal evaporator; then the film was thermally oxidized in a tube furnace at 500 °C for 3 h to get NiO film. The film revealed polycrystalline structure of cubic NiO phase as confirmed from XRD characterization. The diffraction peaks ascribed to metallic Ni film were not detected in the XRD pattern which implies that Ni film was completely converted into NiO. For photoelectric measurements of NiO/Si heterojunction, Ag metal was deposited on both Si substrate and NiO film as a contact. The current-voltage curves exhibited rectifying behaviour with ideality factor and barrier height of 25 and 0.96 eV, respectively. NiO/Si heterojunction showed appreciable photoresponse towards UV light at wavelength of 365 nm. The responsivity, rise time and fall time of the photodiode were measured as 0.16 A/W, 1.7 s and 0.85 s, respectively at bias voltage of -5 V.

Humidity-Tolerant Ultrathin NiO Gas-Sensing Films.

When the gas sensor active layer film thickness is decreased, increased sensitivity to changes in the adsorbate concentration is expected when measuring the resistance of the layer, in particular when this thickness is on the order of the Debye length of the material (one-tens of nanometers); however, this is demonstrated only for a limited number of materials. Herein, ultrathin NiO films of different thicknesses (8-21 nm) have been deposited via chemical vapor deposition to fabricate gas sensor devices. Sensor performance for a range of NO2 concentrations (800 part-per-billion to 7 part-per-million) was evaluated and an optimum operating temperature of 125 °C determined. The dependence of the potential relative changes with respect to the NO2 concentration and of the sensor signal with respect to the geometrical parameters was qualitatively evaluated to derive a transduction model capable of fitting the experimental results. The selective sensitivity toward NO2 was confirmed by the limited response for different reducing gases, CO, CH4, NH3, and SO2, under optimum operating conditions, and the sensor signal toward NO2 increased with decreasing thickness, demonstrating that the concept of a Debye length dependence of sensitivity is applicable for the p-type semiconductor NiO. In addition, these NiO sensors were exposed to different relative levels of humidity over a wide range of operating temperatures and were found to display humidity tolerance far superior to those in previous reports on SnO2 materials.

SnO2 recycled from tin slime for enhanced SO2 sensing properties by NiO surface decoration

Tin slime is a byproduct of the electroplating tin production line. Tin slime is an important secondary resource, the main component of which is SnO2. In this paper, we discussed an environmentally friendly method to recover SnO2 from tin slime. The recovered SnO2 decorated by NiO has an excellent sensing response to SO2. The morphology, structure and surface state of the prepared materials were characterized by X-ray diffraction (XRD), N2 adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray phoyoelectron spectroscopy (XPS), and Raman spectroscopy. The SnO2 dispersed by PEG-400 exhibits smaller and more dispersed nanoparticles, which show responses of 6.5–100 ppm SO2 at 300 °C. Compared to the SnO2 sensor, the NiO surface decorated SnO2 sensor has significantly enhanced SO2 sensing performance, with a higher gas response, lower operating temperature and better selectivity. The sensing response of the NiO surface decorated SnO2 material to 100 ppm SO2 at 240 °C is as high as 10.38. This result likely occurs due to the increased oxygen vacancies and the formation of the p-n heterojunction between n-type SnO2 and p-type NiO. Importantly, this research has developed a simple and efficient method to recover SnO2 from the secondary resource tin.

Synthesis and Characterization of Spinel Cobaltite (Co3O4) Thin Films for Function as Hole Transport Materials in Organometallic Halide Perovskite Solar Cells

Conventional inorganic p-type conductive oxides, for example, NiO, CuOX, and CuCrOX, can serve as low-cost and efficient hole transport materials for wide-bandgap organolead halide perovskites [for...

Hierarchical WO3–NiO microflower for high sensitivity detection of SF6 decomposition byproduct H2S

In this work, hierarchical WO3–NiO microflowers have been designed and prepared through a controllable hydrothermal route for high sensitivity detection of H2S produced by SF6 decomposition. The hierarchical flower-like nanostructures assembled with numerous nanosheets were influenced by the introduction of WO3, which is regarded as a significant strategy for improving the gas sensing properties. The synthesized nanostructures were tested by various characterization to investigate the different microstructures of the nanocomposites. The H2S sensing performances of the sensors fabricated with these flower-like nanostructures were measured, which indicated that 3.0 at% WO3–NiO microflower based sensor possessed excellent properties such as higher gas responses and more prominent repeatability compared with those of other fabricated sensors. The enhanced performances might be mainly ascribed to the creation of the heterojunction at n-type WO3 and p-type NiO interface, which caused the improvement of the potential barrier and depletion layer. In addition, the larger specific surface area of flower-like nanostructures also possessed abundant sites for surface reaction.

The blue luminescence of p-type NiO nanostructured material induced by defects: H2S gas sensing characteristics at a relatively low operating temperature

The detection of hazardous and toxic gases in homes and corporate world, with highly sensitive and selective manner continues to be of great interest. Therefore, we report on the gas sensing characteristics of NiO nanostructures with crystallite sizes of approximately 10–17 nm prepared by a co-precipitation method using various reaction times ranging from 2 to 24 h. The physical variation of the colour from green to black after heat treatment was observed due to non-stoichiometric property of NiO revealing blue emission, which was assigned to oxygen and/or nickel vacancies. The diffuse reflectance spectra revealed a wide direct band gap in the range of 3.4–3.6 eV. The high BET surface area ranging from 46 to 84 m2/g was witnessed. The NiO-8 h sensor revealed an excellent response of 74 towards 60 ppm of H2S at 75 °C in dry air. The detection limit of 0.013 and 1.6 ppm was observed for NiO-8 h based sensor in dry air and RH-40%, respectively. These findings specify that the NiO-8 h sensor has pronounced potential for applications in high-performance H2S gas sensor operating at low temperature. The underlying mechanism for the improved NiO-8 h sensing performance is debated.

One-step fabrication of 1D p-NiO nanowire/n-Si heterojunction: Development of self-powered ultraviolet photodetector

Even though there are reports on NiO-p/Si-n based photodetector, work along 1D NiO/Si self-powered photodetector remains unexplored. 1D materials offer better electron mobility and can provide ballistic transport channel, which helps in achieving high responsivity. In this work, direct single-step deposition of p-type NiO nanowires on n-type Si as a self-powered photodetector was successfully fabricated by engaging simple electrospinning technique. The structural properties as observed from XRD indicate highly crystalline NiO nanowires and FESEM images revealed 60-75 nm diameter with uniform distribution. Growth of nanowires by using stimuli polymer and its completely removal at high temperature was confirmed using TGA and XPS analysis. The responsivity of the fabricated photodetector was calculated to be 9.1 mA W−1 at zero bias, which can be attributed to the p-type NiO interface with the n-type Silicon, which creates an internal electrical field thereby assisting in the effective separation of the photogenerated carriers. Further, under illumination, at zero bias, the photogenerated current still exists suggesting a generation of internal voltage, which makes the fabricated device as self-powered. This fabrication method will enhance the photodetection properties, and it can be implemented in the fields of optoelectronic devices, sensors, and flexible electronics.

1-kV Sputtered p-NiO/n-Ga2O3 Heterojunction Diodes With an Ultra-Low Leakage Current Below $1~\mu$ A/cm2

High performance NiO/β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> heterojunction pn diodes were realized by applying a sputtered p-type NiO film onto a lightly doped n-type β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> epitaxial layer. Taking advantage of the high barrier height against carriers within the pn heterojunction, the demonstrated device exhibited a high breakdown voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) of 1059 V without optimized electric field management techniques, and before breakdown the reverse leakage current density remained below 1 μA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Simultaneously, a relatively low specific on-resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> , <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sp</sub> ) of 3.5 mΩ · cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was achieved. The built-in potential of the heterojunction that determined by a capacitance-voltage (C-V) measurement was around 2.4 eV. As discussed in terms of the energy band diagram of a type-II heterojunction, the conduction band and valence band offsets at the NiO/β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> hetero-interface were estimated to be 1.2 and 2.3 eV, respectively.

Transparent p-type NiO:Al thin films as room temperature hydrogen and methane gas sensors

Transparent Al-doped NiO thin films with thickness of 100 nm were prepared by radio frequency (rf) sputtering technique in order to investigate their response to reducing gases such as hydrogen (H2) and methane (CH4), at room temperature (RT). During deposition, the amount of doping [Al/(Al + Ni)] was 10%, while the O2 content in the Ar–O2 mixture in the plasma was 2.8%. These optimum values were set to obtain films with transmittance over 40% in the visible and optical energy band gap (Eg) of 3.65 eV. All films were polycrystalline, with a crystallite size of 7.9 nm and a lattice constant of 0.42 nm. Moreover, the films showed a smooth surface with root mean square (rms) roughness of 2.87 nm. The p-type electric behavior of the films was identified by current modulated ac-Hall effect measurements. The films were exposed to 100 ppm H2 in synthetic air, at room temperature, showing a typical p-type behavior and a sensitivity of 68%, while the response and recovery times were found to be 388 s and 451 s, respectively. Subsequently, the films were also exposed on CH4 showing a sensitivity of 58%, with response and recovery times equal to 1373 s and 95 s, respectively.

Impact of p-Type NiO Pocket and Ultra-Thin Graphene Layer on the RF Performance of β-Ga2O3 MOSFET

In this work, the RF performance of proposed p-type NiO pocket based β-Ga2O3/graphene heterostructure MOSFET has been investigated. The figure of merits (FOMs) for its performance investigation includes transconductance (gm), output conductance (gd), intrinsic capacitances (gate to drain capacitance Cgd and gate to source capacitance Cgs) and cut-off frequency (fT). The large signal CW RF performance is also investigated which includes output power (POUT), power-added efficiency (PAE) and power gain (Gp) as a key FOMs. The key idea behind this work is to demonstrate a device with improved RF performance and low leakages. The RF characteristics of the proposed device have been studied to show its utility in the wireless applications. The introduction of ultra-thin graphene layer beneath the channel region results in 0.85 times lower Cgs, 1.04 times improvement in fT and 1.5 dB superior GP in comparison to the p-type NiO pocket based β-Ga2O3 (NiO-GO) MOSFET. The proposed structure shows superior RF performance with low leakages.