P-type ZnO Research Articles

Thermal conductivity suppression in ZnO with AlZn2O4and ZnP2for thermoelectric applications.

In this study, intrinsic ZnO powder was sintered and intercalated with particles. The resulting powder, along with a commercial p-type product, was consolidated into bulk materials, and their thermal conductivity was measured across a temperature range of 350 K to 700 K. The thermal conductivity of the commercial p-type ZnO was found to be lower than that of intrinsic ZnO, attributed to controlled doping. Notably, our demonstration illustrated that the thermal conductivity can be reduced by a factor of 5-10 in the presence of AlZn2O4 and ZnP2 precipitates. This methodology presents a feasible approach for the future design of ZnO-based thermoelectric materials, particularly for thermal heat scavenging applications.&#xD.

Giant photoresponse in p-type sodium-doped ZnO films

The detection of ultraviolet radiation is currently a topic that deserves the attention of society. This research shows that the addition of sodium (Na) to ZnO thin films enhances the generation and collection of photogenerated carriers at room temperature, making ZnO:Na a promising candidate for photosensors. This effect is particularly pronounced at 10 % Na-concentration, with a photoresponse around 104, suggesting a decrease in the role of deep traps. Additionally, as a defect engineering approach, annealing in different controlled atmospheres shows that the N2 atmosphere provides a markedly faster photoresponse. By introducing Na atoms into the ZnO crystal lattice, charge compensation levels are formed, inducing the p-type conductivity in some ranges of temperature, particularly at 300 K. Annealing in controlled atmospheres also influences both the transition from n-type to p-type conductivity and light-stimulated phenomena.

Investigations on electrical conductivity and dielectric properties of p-type ZnO by doping N synthesized from sol–gel method

Investigations on electrical conductivity and dielectric properties of p-type ZnO by doping N synthesized from sol–gel method

First-principles calculation study on the mechanism of p-type ZnO through Mi-nNO (M= Mg and Cu) complexes

First principles calculation based on density functional theory is applied to study the possible approach to realize p-type ZnO through Mi-nNO (Mi is an interstitial defect; n = 2 or 3) complexes. In codoping method, the substitutional defects usually serve as the donors in donor-acceptor complexes, which are seen as the source of p-type ZnO. However, our research shows that the interstitial defects can replace the substitutional defects to become the donors. In Mg + N and Cu + N codoped ZnO, the binding, formation and ionization energies of possible complexes are investigated. Mgi-2NO and Cui-NO are two neutral complexes which can introduce a fully occupied impurity band, 0.66 and 0.87 eV above the VBM of the pure ZnO, respectively. It is found that Mgi-3NO and Cui-nNO (n = 2,3) can become the stable source of p-type conductivity under Zn-rich condition. In addition, the requirements of “M” in Mi-nNO complex are discussed.

Exploring Na Doping in ZnO Thin Films: Electrical and Optical Insights

Strategies to achieve p-type behavior in semiconductor oxides are an important current topic of research. Our study showed that sodium-doped zinc oxide thin films are a plausible approach. The insertion of dopant allowed a transition between n-type p-type electrical behavior in specific temperature ranges around 300 K. Annealing procedures under controlled atmospheres, including Ar, N2, and O2, increased the hole density up to a magnitude of 1016 cm−3, although this also reduced the window temperature. The micro-photoluminescence spectra showed an enhancement of defect-related emissions as the dopant content increased. Notably, yellow-green emissions (around 2.38 eV–520 nm) were the most prominent in the as-grown samples. After annealing, a strong redshift of the defect band was observed (around 1.85 eV–670 nm). Our findings showed that p-type ZnO:Na films exhibited emissions associated with RGB primary colors. In a chromaticity diagram, as-grown samples appeared near the white range, annealed films were close to the warm white area, and O2 annealed films trended within the red range.

Reaction solution mediated photo-degradation process and mechanism of tetracycline via semiconductor-insulator composite ZnO:N-BaSO4

Research in contaminants photo-degradation has witnessed significant progress, recently insulator-based catalysts gaining prominence. In this study, N-containing p-type ZnO decorated BaSO4 (ZnO:N-BaSO4) were synthesized and presented a pseudo-first-order kinetic constant of 1.30 × 10−2 min−1 for TC degradation, surpassing that of ZnO:N and their physical mixture by four and seven-fold, respectively. Impressively, the electron transfer in ZnO:N/TC solution interface led to band bending on ZnO:N surface and realized the band matching between ZnO:N and BaSO4. Density functional theory (DFT) calculations unveiled that the strong Zn-O covalent interaction involving 4s states of Zn atoms and 2p states of O atoms, established a distinctive pathway for electron transfer from semiconductor to insulator. Moreover, the catalysts demonstrated robust activity and sustained long-term stability in real wastewater and surface water. This research illuminates the role of wastewater redox potential in semiconductor band adjustment and highlights abundant, eco-friendly insulators as co-catalysts for selective photo-degradation.

Tailoring p-Type Behavior in ZnO Quantum Dots through Enhanced Sol-Gel Synthesis: Mechanistic Insights into Zinc Vacancies.

The synthesis and control of properties of p-type ZnO is crucial for a variety of optoelectronic and spintronic applications; however, it remains challenging due to the control of intrinsic midgap (defect) states. In this study, we demonstrate a synthetic route to yield colloidal ZnO quantum dots (QD) via an enhanced sol-gel process that effectively eliminates the residual intermediate reaction molecules, which would otherwise weaken the excitonic emission. This process supports the creation of ZnO with p-type properties or compensation of inherited n-type defects, primarily due to zinc vacancies under oxygen-rich conditions. The in-depth analysis of carrier recombination in the midgap across several time scales reveals microsecond carrier lifetimes at room temperature which are expected to occur via zinc vacancy defects, supporting the promoted p-type character of the synthesized ZnO QDs.

Application of Two-dimensional P-type ZnO Powder Illuminated By Visible Light for the Inhibition of Gram-positive and Gram-negative Bacteria in Water

Bacteria affect food quality in developing countries by spreading through contaminated soils and water. Antibiotics are used indiscriminately to eliminate Gram-positive and Gram-negative bacteria, with varying degrees of success. The use of nanomaterials with bactericidal properties can minimize the overuse of antibiotics. In this study, a two-dimensional p-type ZnO powder was successfully synthesized and its bactericidal properties were demonstrated. The XRD and Raman spectroscopy results indicated the presence of wurtzite-phase ZnO with Oi as the predominant native defect, resulting in p-type conductivity. SEM analysis confirmed the two-dimensional morphology, and optoelectronic characterization revealed a bandgap of 3.17 eV. Despite this high bandgap value, a plasmonic effect was generated on the surface of two-dimensional ZnO, which enhanced its bactericidal properties when the powders were in contact with bacteria. From an initial colony level of 5.5 × 105 CFU/mL, a significant decrease in the number of Gram-positive bacteria to 1.15 × 105 CFU/mL was observed, whereas the number of Gram-negative bacteria slightly increased to 1.45 × 106 CFU/mL. The observed inhibition rates were higher than those achieved with the broad-spectrum antibiotic, as validated in this study. The use of two-dimensional ZnO may provide a sustainable solution for the eradication of waterborne pathogens using visible light alone.

Visible Light Induced Photocatalytic Removal of Methylene Blue Using Cu-tunable p-type ZnO Nanoparticles.

Removal of phototoxicity and zootoxicity pollutants from the aqueous environment is of great importance to human and aquatic life. Copper-tunable p-type zinc oxide (Cu-ZnO) photocatalysts have been prepared by the chemical co-precipitation method. The structural, morphological, elemental and optical properties of the obtained catalysts were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray (EDX) analysis and ultraviolet-visible (UV-Vis) spectrophotometry. The diffraction patterns of the as-synthesized catalysts were matched with that of the hexagonal wurtzite structure for the standard ZnO nanoparticles. The photocatalytic activity of the prepared Cu-doped ZnO catalyst was evaluated using methylene blue (MB) dye under various conditions. The effect of operational parameters such as MB initial concentration, catalyst dosage, and solution pH was optimized using a face central composite design (FCCD) of the response surface methodology (RSM). The optimum photodegradation efficiency of 98.00% was found at 0.30g/L catalyst dose, 10.00mg/L initial concentration of MB and initial pH at 6.00. The degradation model was statistically remarkable with p < 0.0001% in which the MB initial concentration and solution pH were the most significant variables influencing the removal of MB over the Cu tunable p-type ZnO photocatalyst under visible light irradiation. Finally, the photocatalytic degradation of MB using the undoped and Cu-doped ZnO nanoparticles was nicely fitted pseudo-first-order kinetics scheme.

Density functional theory study of adsorption of organic molecules on ZnO monolayers: Implications for conduction type and electrical characteristics

Graphene-like ZnO monolayer, a typical two-dimensional material, has garnered enormous research attention due to its desirable optoelectronic properties and potential broad applications. However, the difficult in fabricating p-type ZnO material is still undergoing. Herein, the atomic and electronic properties of the adsorption of the selected organic molecules including electrophilic molecule tetracyano-p-quinodimethane (TCNQ) and nucleophilic molecule tetrathiafulvalene (TTF) on ZnO monolayers are carried out by the first-principles calculations. The results indicate that the adsorption of TCNQ on the ZnO monolayer leads to typical p-type doping, with a small gap (Ep) between the lowest unoccupied molecular and the valance band maximum with shallow acceptor states in the middle gap. However, the adsorption of TTF can obtain n-type doping of ZnO monolayer with the large gap (En) between the highest occupied molecular and the conduction band minimum with deep donor states. For TCNQ-ZnO monolayer, it exhibits the enhancement absorb in solar energy. There is a considerable charge transfer and strong non-covalent interaction between TCNQ and ZnO monolayer. The work function of TCNQ-ZnO ML is higher than that of pristine ZnO ML. However, the adsorption of TTF can significantly reduce the work function of ZnO ML, turning it into an n-type conduction semiconductor. Additionally, upon the adsorption of organic molecules, the layer thickness and the interlayer coupling as well as the adsorption concentration can modify the band gap of ZnO, and further tune the conduction type of ZnO. Remarkably, applying electric field can alter the number of hole and further greatly tune the electrical characteristic of TCNQ-ZnO ML. The current results can promote the applications of two-dimensional ZnO in nanoelectronics and optoelectronics.

Room temperature deposition of stable p-type ZnO:N thin films through chemical species modulation using reactive pulsed laser deposition

Low temperature processing as well as long-term electrical stability are required to match p-type ZnO thin films with flexible electronics applications. Herein, ZnO and ZnO:N thin films were deposited at room temperature by reactive pulsed laser deposition of a zinc metallic target. Several ZnO thin films were obtained by varying the oxygen working pressure from 1.2 × 10-5 Torr to 3.5 × 10-2 Torr. Chemical concentration was smoothly tuned as demonstrated by in situ X-ray Photoelectron Spectroscopy. Introducing and varying both N2 and O2 fluxes at a constant pressure, N-doped ZnO films from 0.3 at.% to 5 at.% were deposited. Adjusting the N2/O2 flux ratio, p-type ZnO:N films were successfully achieved, exhibiting a carrier concentration of 5.3 × 1018 cm−3, resistivity of 2 Ωcm, and mobility of 0.5 cm2V-1s−1. Four representative p-type samples were analyzed to confirm chemical and electrical reproducibility. Electrical properties of one of these films were measured again nine months after deposited, and p-type conductivity was still observed. Cathodoluminescence revealed green-dominant emissions in n-ZnO and UV-dominant emissions in p-ZnO:N films as nitrogen doping effect. Finally, a p-n diode was fabricated using photolithography, exhibiting rectification performance even nine months after deposited. P-type ZnO:N presented here are suitable for flexible electronics devices fabrication.

Carbon-Tunable p-type ZnO Nanoparticles for Enhanced Photocatalytic Removal of Eriochrome Black T

Zinc oxide-mediated photocatalysis is a promising alternative to TiO2 photocatalysis, especially for the purpose of removal of recalcitrant organic dye pollutants. Highly crystalline, nanoscopic carbon-doped ZnO was successfully synthesized via combined precipitation and mechanochemical approach and characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray (EDX) and Fourier transform infrared (FTIR) spectrometry. The obtained photocatalysts depict plate-like morphology and hexagonal wurtzite structure. The XRD, SEM, and FTIR analyses were in good agreement with EDX results. The 5wt % C-doped ZnO showed remarkable visible light-photocatalytic activity based on the degradation of Eriochrome Black T (EBT), and exhibits the best point of zero charge (pHpzc) for a favorable adsorption equilibrium. This degradation process was optimized at 97 % using response surface methodology (RSM) using a 0.1 g C-ZnO, 5.00 mg/L EBT and pH 11. The associated kinetic data fit the pseudo-first-order kinetic model. The resulting C-ZnO was a p-type with a good pH at zero-point charge that permits the substantial removal of EBT by C-doped under visible light irradiation over a wide range of initial pH.

A Spectroscopic Evaluation of the Generation Process of Semiconductor Nanoparticles (ZnO) by DC Arc Plasma

The fabrication of ZnO nanoparticles (NPs) was monitored and studied in situ by controlling the plasma parameters of the direct current (DC) arc plasma system, such as the current density and chamber pressure. The optical emission signature of nitrogen was spectroscopically studied using optical emission spectroscopy (OES) techniques, and it showed a dependency on the nitrogen concentration in the ZnO nanoparticles in relation to the output of the ZnO NPs-based homojunction light-emitting diodes (LEDs). The synthesized NPs had a good crystalline quality and hexagonal wurtzite structure, and they were characterized by X-ray diffraction (XRD) techniques and scanning electron microscope (SEM). The photoluminescence properties of the ZnO NPs and the optical and electrical parameters of the LEDs were also analyzed and correlated. The results indicate that the nitrogen dopants act as acceptors in the ZnO NPs and are favored in low plasma temperatures during fabrication. We anticipate that the results can provide an effective way to realize reliable nitrogen-doped p-type ZnO and tremendously encourage the development of low-dimensional ZnO homojunction LEDs.

Synthesis and optical properties of phosphorus doped ZnO: X-ray absorption, X-ray emission, and X-ray excited optical luminescence studies

Abstract Over the past decades, zinc oxide semiconductor and its derivatives have been extensively developed because of its optoelectronic properties. Since ZnO is an intrinsic n-type semiconductor, how to synthesize high-quality p-type ZnO semiconductors and investigate their optoelectronic properties and local chemical structures are important and necessary. In this article, two studies of synthesizing both undoped and phosphorus-doped ZnO nanostructures by hydrothermal method and chemical vapor deposition (CVD) technique are presented. Scanning electron microscopy (SEM) and laboratory X-ray diffraction (XRD) are used to track the surface morphology and the crystalline structure of both undoped and phosphorus doped ZnO nanostructures, respectively. X-ray absorption near edge structures (XANES), X-ray emission spectroscopy (XES) and X-ray excited optical luminescence (XEOL) are also used to determine the local chemical information of both undoped and phosphorus-doped ZnO nano/microstructures such as local symmetry and optical properties. It is found that the phosphorus is successfully doped into the surface of ZnO and substituted the Zn. The phosphorus-doped ZnO products have better crystallinity and less oxygen vacancies on the surface. These two are correlated as one leads to the other. The XEOL results suggest that the average bandgap for undoped and phosphorus doped ZnO is the same, 3.24 eV. The second derivative of the absorption-emission spectra yields the fundamental bandgap for undoped ZnO and phosphorus-doped ZnO is 3.25 eV. The implication of this observation is discussed.

First-principles study on p-type transformation of ZnO doped by Ag element

The optical properties of intrinsic ZnO and Ag-doped ZnO for p-type transformation with different concentrations is studied using the first principles. The results show that the lattice constant and cell volume increase after Ag doping, and the total energy of the system gradually decreases, and the structure becomes more stable with the increase of Ag doping concentration. In supercell of Zn13Ag3O16, the impurity level is reduced, so the required ionization energy is reduced, which contributing to the ionization of impurity, leading to the significant improvement of charge transfer, hence, the conductivity is enhanced. Both absorption and reflection spectra appear red shift with the increase of Ag doping concentration, and the peak intensity is significantly increased with a higher Ag doping concentration. High Ag concentration is beneficial to the stability of p-type ZnO and the enhancement of photoelectric characteristics, which provides a basis for the application of ZnO in optoelectronic devices.

Ultraviolet Exciton-Polariton Light-Emitting Diode in a ZnO Microwire Homojunction.

Low-dimensional ZnO, possessing well-defined side facets and optical gain properties, has emerged as a promising material to develop ultraviolet coherent light sources. However, the realization of electrically driven ZnO homojunction luminescence and laser devices is still a challenge due to the absence of a reliable p-type ZnO. Herein, the sample of p-type ZnO microwires doped by Sb (ZnO:Sb MWs) was synthesized individually. Subsequently, the p-type conductivity was examined using a single-MW field-effect transistor. Upon optical pumping, a ZnO:Sb MW showing a regular hexagonal cross-section and smooth sidewall facets can feature as an optical microcavity, which is evidenced by the achievement of whispering-gallery-mode lasing. By combining an n-type ZnO layer, a single ZnO:Sb MW homojunction light-emitting diode (LED), which exhibited a typical ultraviolet emission at a wavelength of 379.0 nm and a line-width of approximately 23.5 nm, was constructed. We further illustrated that strong exciton-photon coupling can occur in the as-constructed p-ZnO:Sb MW/n-ZnO homojunction LED by researching spatially resolved electroluminescence spectra, contributing to the exciton-polariton effect. Particularly, varying the cross-sectional dimensions of ZnO:Sb wires can further modulate the exciton-photon coupling strengths. We anticipate that the results can provide an effective exemplification to realize reliable p-type ZnO and tremendously promote the development of low-dimensional ZnO homojunction optoelectronic devices.

Role of native defects on the opto-electronic properties of p-type ZnO synthesized during the most straightforward method: only water

The influence of predominant native defects in forming ZnO with p-type conductivity is discussed in this work when the semiconductor is synthesized only in water. The semiconductor was prepared by dissolving a Zn-salt in deionized water at 80 °C. The powders were thermally treated at 400 °C in an air atmosphere to obtain well-defined crystalline ZnO. XRD, SEM, EDS, Raman spectroscopy, diffuse reflectance, photoluminescence, and Seebeck effect techniques were used to characterize the synthesized material. The results showed a well-crystalline semiconductor in wurtzite phase. The crystal-oriented growth was the (002) plane. The sample morphology was formed by highly ordered sticks-like. The optoelectronic characterization showed that the synthesized ZnO had a lower band gap than that reported in the literature. It was related to deep energy levels corresponding to oxygen interstitials as the predominant native defects. Raman, EPR, and photoluminescence spectra analysis corroborated the existence of native defects in the crystalline structure. The p-type conductivity of the sample was determined by Seebeck coefficient analysis. A synthesis reaction mechanism involving the formation of oxygen interstitials was proposed in this work. Understanding the effects of native defects in wide band gap semiconductors is necessary to design new materials for sensors or energy conversion applications.

Tailoring Sb doping concentration to achieve p-type nanostructured ZnO thin film grown by sol–gel method

Tailoring Sb doping concentration to achieve p-type nanostructured ZnO thin film grown by sol–gel method

Piezoelectricity-enhanced photoelectrochemistry synthesis of H2O2 on an Au nanoparticles modified p-type Sb-doped ZnO nanotubes array.

A p-type Sb-doped ZnO nanorods (p-ZnOSb,NR) array was hydrothermally prepared on indium tin oxide (ITO) and then etched into a p-type Sb-doped ZnO nanotubes (p-ZnOSb,NT) array by hot alkali solution. Further photodeposition of Au nanoparticles (AuNP) yielded a novel AuNP/p-ZnOSb,NT/ITO photocathode. The green synthesis of H2O2 by piezoelectricity-enhanced photoelectrochemistry and oxygen reduction reaction was studied for the first time, giving a H2O2 yield of 15.2 μmol cm-2 h-1, a photocurrent density of -1.05 mA cm-2 and a Faraday efficiency of 79.0% on this photocathode.

An individual ZnO microwire homojunction LED with ultraviolet electroluminescence spectrally purified using Pt nanoparticles cladding

Low-dimensional ultraviolet light sources are enormous significance due to their wide range of potential applications, ranging from bioscience and high-resolution biological imaging, environmental conservation to public hygiene. Nevertheless, developing energy-efficient and cost-efficient light sources still remains serious challenges. In this study, p-type ZnO microwires with Sb-incorporation (ZnO:Sb MWs) were synthesized individually. The p-type conductivity was proofed using an individual MW based back-gated field-effect transistor; while the ZnO:Sb MWs with quadrilateral cross-section exhibited stimulated emission resonant in well-defined Fabry-Perot mode on the benefit of single-crystalline quality and atomically smooth side facets. The newly synthesized ZnO:Sb MW was further used to fabricate homojunction light-emitting device by employing n-type ZnO film as electron-transporting layer. A strong ultraviolet emissions peaking at around 378.5 nm was achieved upon forward biased electrically, but illustrating much broader electroluminescence (EL) linewidth. Introducing Pt nanoparticles (PtNPs) with desired plasmons, the light-out intensity is significantly enhanced. Particularly, the broad EL profiles narrowed to about 16.6 nm at high injection regime, achieving electron-holes radiative recombination in the ZnO:Sb MWs active region. The results exhibit a prominent progress achieving high-quality ZnO nano/microstructures with genuine p-type conductivity, which has great hopes for its future applications and development in ZnO homojunction optoelectronic devices.