Co-doped Zinc Oxide Research Articles

Mass production and photoelectric performances of P and Al Co-doped ZnO nanocrystals under different cooling post-processes

The phosphorus and aluminum co-doped in zinc oxide (ZnO) called PAZO nano-crystals (NCs) have been mass synthesized by a combustion method, which shows a preferable photocatalytic capability and conductive ability. This article focuses on the properties of PAZO NCs experienced by three cooling-down aftertreatments, which were the normalizing, quenching and annealing process, respectively. The influences of different cooling processes on the photocatalytic and conductive performances are discussed in details. From the research, we found the quenched-PAZO NCs showed the most unappealing photocatalysis and conductivity, because excessive defects as the recombination center of electron–hole pairs were generated in the quenching process.

Effect of oxidation temperature and high magnetic field on the structure and optical properties of Co-doped ZnO prepared by oxidizing Zn/Co bilayer thin films

Co-doped zinc oxide (ZnO) films were fabricated by oxidizing Zn/Co bilayer thin films prepared by vacuum evaporation. The effects of oxidation temperature and high magnetic field on the structure and optical transmittance were investigated. The results show that Co-doped ZnO films in the absence of a magnetic field prefer to grow in a coral dendrite-like morphology. This morphology is inhibited by the Lorentz force of a high magnetic field. Elevating the oxidation temperature to 600 °C from 450 °C can lead to more Zn ions being substituted by Co ions. However, the increase in Co substitution can be inhibited by a high magnetic field. According to X-ray photoemission spectroscopy results, the chemical states of Co are affected by the oxidation temperature and a high magnetic field. Co2+ distributes uniformly in the host ZnO lattice at 450 °C. However, CoO and Co3O4 form at 600 °C without a magnetic field. The obvious energy differences for Co 2p indicate that the Co chemical state changes with the application of a high magnetic field. These results thus show that a high magnetic field can be used to modify the state of Co in ZnO films. Optical transmittance data show that the Co state, O vacancies, and crystallinity have no obvious influence on the transmittance, which is strongly related to the dendrite-like structure.

Investigations on the structural and optical properties of band gap engineered Zn1−x(Cd, Mg)xO thin films deposited by sol–gel technique

Cadmium and magnesium co-doped zinc oxide (ZnO) thin films have been deposited on sapphire substrates using the sol–gel method and the spin coating technique. X-ray diffraction studies confirmed that the deposited films exhibit a hexagonal wurtzite ZnO structure. A strong ultraviolet near-band-edge emission and a deep level emission were observed in the room temperature photoluminescence (PL) spectra of all the films. The PL spectra were also investigated as a function of temperature to examine the emission mechanism of the deposited films. The ability to vary the band gap energy from 3.1 to 3.6 eV was realised by adjusting the cadmium and magnesium concentration in the co-doped ZnO films. X-ray photoelectron spectroscopy studies revealed the successful incorporation of cadmium and magnesium in the ZnO films.

Preparation and Thermoelectric Properties of Co-Doped ZnO Synthesized by Sol-Gel.

Zinc oxide (ZnO) has attracted increasing attention as one of the most promising n-type thermo-electric materials, but its practice use was limited by high thermal conductivity and low electrical conductivity. Therefore, we herein prepared Co-doped ZnO nanoparticles by sol-gel method and then compressed nanoparticles into bulk materials through spark plasma sintering. The thermo-electric properties, including electrical conductivity, Seebeck coefficient, thermal conductivity, and ZT value, have been investigated. We found that the substitution of Co2+ causes the decrease of bandgap and the increase of carrier concentration, thus the improvement of electrical conductivity. At the same time, the Co-induced lattice distortion and nanoparticles reduce the thermal conductivity by shortening the mean free path (MFP) of the phonons. The resultant ZT is 0.037 for Zn0.9Co0.1O, which is more than 23-fold higher than that of the pure ZnO samples.

Effect of small changes in sintering temperature on varistor properties and degradation behavior of V–Mn–Nb–Gd co-doped zinc oxide ceramics

The effect of small changes in sintering temperature on microstructure, electrical properties, dielectric characteristics, and degradation behavior of V–Mn–Nb–Gd co-doped zinc oxide ceramics was investigated. With the increase of sintering temperature, the densities of the sintered pellets decreased from 5.54 to 5.42 g/cm3 and the average grain size increased from 4.1 to 11.7 μm. The breakdown field (E1 mA) decreased noticeably from 7138 to 920 V/cm with the increase of sintering temperature. The varistor ceramics sintered at 900 °C exhibited excellent nonohmic properties, which were 66 for the nonohmic coefficient and 77 μA/cm2 for the leakage current density. Concerning stability, the varistors sintered at 900 °C exhibited the strongest accelerated degradation characteristics, with ΔE1 mA =–9.2% for DC accelerated degradation stress of 0.85 E1 mA at 85 °C for 24 h.

Structure and properties of Co-doped ZnO films prepared by thermal oxidization under a high magnetic field.

The effect of a high magnetic field applied during oxidation on the structure, optical transmittance, resistivity, and magnetism of cobalt (Co)-doped zinc oxide (ZnO) thin films prepared by oxidizing evaporated Zn/Co bilayer thin films in open air was studied. The relationship between the structure and properties of films oxidized with and without an applied magnetic field was analyzed. The results show that the high magnetic field obviously changed the structure and properties of the Co-doped ZnO films. The Lorentz force of the high magnetic field suppressed the oxidation growth on nanowhiskers. As a result, ZnO nanowires were formed without a magnetic field, whereas polyhedral particles formed under a 6 T magnetic field. This morphology variation from dendrite to polyhedron caused the transmittance below 1,200 nm of the film oxidized under a magnetic field of 6 T to be much lower than that of the film oxidized without a magnetic field. X-ray photoemission spectroscopy indicated that the high magnetic field suppressed Co substitution in the ZnO lattice, increased the concentration of oxygen vacancies, and changed the chemical state of Co. The increased concentration of oxygen vacancies affected the temperature dependence of the resistivity of the film oxidized under a magnetic field of 6 T compared with that of the film oxidized without a magnetic field. The changes of oxygen vacancy concentration and Co state caused by the application of the high magnetic field also increase the ferromagnetism of the film at room temperature. All of these results indicate that a high magnetic field is an effective tool to modify the structure and properties of ZnO thin films.

Experimental and first-principles DFT studies of electronic, optical and magnetic properties of cerium–manganese codoped zinc oxide nanostructures

Syntheses, structural, optical and magnetic characterizations of codoped ZnO nanoparticles have been reported. Nanoparticles of Zn1−2xCexMnxO (x=0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) were synthesized using a microwave-assisted combustion method. Structural, optical and magnetic properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL) and a vibrating sample magnetometer (VSM). The observed shift in XRD peak position, change in peak intensity, cell parameters, volume and stress confirmed the substitution of cerium-manganese (Ce–Mn) dopants within ZnO lattice. The synthesized nanoparticles show different microstructure without changing the parent hexagonal wurtzite structure of zinc oxide (ZnO). The average crystallites size was decreased from 43 to 21nm. Energy dispersive X-ray spectra confirmed the presence of Ce and Mn in ZnO system and the weight percentage was nearly equal to their nominal stoichiometry. DRS analysis showed a decrease in the energy gap with increasing dopants content. The observed luminescence in the green, violet and blue regions strongly depends on the nature of the doping elements and their concentration owing to the formation of different oxygen vacancy, zinc interstitial, and surface morphology. Our results demonstrate that Mn ions doping concentration play an important role in the observed room temperature ferromagnetism (RTFM) of Ce–Mn codoped ZnO nanoparticles. First- principles calculation results indicate that Ce governs the stability, while Mn adjusts the magnetic characteristics in codoped ZnO.

Effects of substrate temperature on the structural, morphological, electrical and optical properties of Al and Ga co-doped ZnO thin films grown by DC magnetron sputtering

In this work, Al and Ga co-doped zinc oxide (AGZO) thin films were deposited on glass substrates by DC magnetron sputtering under different substrate temperatures. Evolutions of the structural, morphological, electrical and optical properties of the AGZO thin films as a function of substrate temperature were analyzed. Results showed that the average transmittance in the visible range (400–800nm) for all the thin films was over 82%, which did not change obviously with the substrate temperature. The average grain size increased from 20.6nm to 51.4nm and the RMS surface roughness decreased from 21.1nm to 4.0nm with substrate temperatures ranging from 150°C up to 450°C. The carrier concentration, Hall mobility of the thin films increased when the substrate temperature was increased from 150°C to 350°C, and then decreased with a further increase of substrate temperature. The film deposited at 350°C exhibited a lowest resistivity of 3.0×10−4Ωcm with the highest carrier concentration of 5.0×1020cm−3 and Hall mobility of 42cm2V−1s−1.

Influence of Al-, Co-, Cu-, and In-doped ZnO buffer layers on the structural and the optical properties of ZnO thin films

Zinc oxide (ZnO) thin films without a buffer layer and with Al-, Co-, Cu-, and In-doped ZnO buffer layers were prepared by using the sol-gel spin-coating method. For the first time, the effects of the ZnO buffer layers doped with different metal materials on the structural and the optical properties of the ZnO thin films are investigated. The surface morphologies of the ZnO thin films having wrinkle structures significantly depended on the type of buffer layer. The largest crystallite size and the highest c-axis orientation were observed for the ZnO thin film with a Co-doped ZnO buffer layer. However, the transmittance for the ZnO thin films with metal-doped buffer layers was slightly decreased compared to that without the buffer layer, and metal-doped ZnO buffer layers hardly affected the optical band gap of the ZnO thin films.

Near infrared broadband from Er-Tm codoped zinc oxide and temperature-dependent properties

Er-Tm codoped ZnO thin film is synthesized by co-sputtering from separated Er, Tm, and ZnO targets. A flat and broad emission band is achieved in a range of 1400-2100 nm by optimizing annealing temperature, and the observed 1460, 1540, 1640 and 1740 nm emission bands are attributed to the transitions of Tm3+: 3H4 →3F4, Er3+ 4I13/2 →4I15/2, Tm3+ 1G4 → 3F2 and Tm3+ 3F4 → 3H6 transitions, respectively, which cover S, C, L, U bands. The intensity ratios of 1640 to 1535 nm and 1740 to 1535 nm below 1000 ℃ are nearly constant, while the ratios increase sharply above 1000 ℃. The temperature dependence of photoluminescence (PL) spectrum is studied under 10-300 K. With increasing the operation temperature, the bandwidth of broadband is nearly invariable (340-360 nm), and the Tm3+ PL emission intensities of 1640 nm and 1740 nm from Er-Tm co-doped ZnO thin film decrease by a factor of 1.5 and 2, respectively. Moreover, the 1535 nm emission intensity is increased by a factor of 1.2. This phenomenon is attributed to the complicated energy transfer (ET) processes involving both Er3+ and Tm3+ and the increase of phonon-assisted ET rate with temperature as well. And the cross relaxation between Tm3+ ions does not occur.

Effect of Sintering Temperature on Microstructure, Electrical and Dielectric Properties of (V, Mn, Co, Dy, Bi)-Codoped Zinc Oxide Ceramics

The effect of sintering temperature on the microstructure, electrical and dielectric properties of (V, Mn, Co, Dy, Bi)-codoped zinc oxide ceramics was investigated in this study. An increase in the sintering temperature increased the average grain size from 4.7 to and decreased the sintered density from 5.47 to . As the sintering temperature increased, the breakdown field decreased greatly from 6027 to 1659 V/cm. The ceramics sintered at were characterized by the highest nonlinear coefficient (36.2) and the lowest low leakage current density (). When the sintering temperature increased, the donor concentration of the semiconducting grain increased from to , and the density of interface state increased from to . The dielectric constant increased greatly from 412.3 to 1234.8 with increasing sintering temperature.

분무열분해법(Spray Pyrolysis)에 의한 알루미늄 산화물과 보론 산화물이 함께 도핑된 산화아연(AZOB: Al<sub>2</sub>O<sub>3 </sub>and B<sub>2</sub>O<sub>3</sub> Co-doped Zinc Oxide)의 분말 제조에 대한 연구

분무열분해법(Spray Pyrolysis)에 의한 알루미늄 산화물과 보론 산화물이 함께 도핑된 산화아연(AZOB: Al<sub>2</sub>O<sub>3 </sub>and B<sub>2</sub>O<sub>3</sub> Co-doped Zinc Oxide)의 분말 제조에 대한 연구

Degradation Characteristics of Pr/Co/Cr/Er Co-doped Zinc Oxide Varistors by Impulse Current Stress

In light of the sure protection function, the most important factors of a varistor are the clamping voltage ratio and degradation characteristics. The degradation characteristics of Pr/Co/Cr/Er co-doped zinc oxide varistors were investigated by impulse currents (0.4~2.1 kA) stress for the specified content of (0.5 and 2.0 mol%). The varistor doped with 2.0 mol% exhibited the best clamp characteristics, with the clamp voltage ratio (K) in the range of K

Effects of post anneal for the INZO films prepared by ultrasonic spray pyrolysis

Indium-nitrogen co-doped zinc oxide thin films (INZO) were prepared on glass substrates in the atmosphere by ultrasonic spray pyrolysis. The aqueous solution of zinc acetate, ammonium acetate and different indium sources: indium (III) chloride and indium (III) nitrate were used as the precursors. After film deposition, different anneal temperature treatment as 350, 450, <TEX>$550^{\circ}C$</TEX> were applied. Electrical properties as concentration and mobility were characterized by Hall measurement. The surface morphology and crystalline quality were characterized by SEM and XRD. With the activation energy analysis for both films, the concentration variation of the films at different heat treatment temperature was realized. Donors correspond to zinc related states dominate the conduction mechanism for these INZO films after <TEX>$550^{\circ}C$</TEX> high temperature heat treatment process.

Yellowish-White Emission from Sol-Gel Mediated Lithium and Aluminium Co-Doped Zinc Oxide Thin Films

Li and Al codoped ZnO (LAZO) thin films have been prepared by sol-gel method. There are two emission bands were observed in the spectra of pure ZnO thin films. One band possessed a sharp peak at round 380 nm locating in the UV range; the other band consists of green luminescence. Yellowish-white emission were observed from the LAZO films, which can be fitted into three bands: a strong yellow emission, a moderate green emission and a weak violet emission centered at 598, 538, and 430 nm, respectively. The luminescence color was seen to be yellowish white due to the recombination for the dominant green and yellow emission.

Effect of Er2O3Content on Nonlinear Properties and Impulse Clamping Characteristics of Pr/Co/Cr/Al Co-doped Zinc Oxide Ceramics

The microstructure, nonlinear properties, and impulse clamping characteristics of Pr/Co/Cr/Al co-doped zinc oxide ceramics were investigated with various contents of Er₂O₃. Increasing Er₂O₃ content increased the density of the sintered pellets from 5.69 to 5.83 g/㎤, and decreased the average grain size from 10.6 to 6.5 μm. With increased Er₂O₃ content, the breakdown field increased from 2318 to 4205 V/cm, and the nonlinear coefficient increased from 19.4 to 40.2. The clamp characteristics were improved with the increase of the content of Er₂O₃. The varistors doped with 2.0 mol% exhibited the best clamp characteristics, in which the clamp voltage ratio was 1.40-1.73 at 1-50 A in an impulse current.

Semiconducting properties of Tm doped Yb-ZnO films by spray pyrolysis

In this work, we have investigated the structural, optical and electrical properties of rare earth co-doped zinc oxide thin films prepared by spray pyrolysis technique. X-ray diffraction has shown that the films are polycrystalline and textured with the c -axis of the wurtzite structure along the growth direction. Scanning electronic microscopy and transmission electronic microscopy were used to study the films composition and morphology. Photoluminescence measurements showed that all the films have a strong emission band at around 380 nm. Layers with electrical resistivity values as low as 5.7 × 10 −2 Ω cm were obtained.

Investigation of structural and optical properties in Cobalt–Chromium co-doped ZnO thin films within the Lattice Compatibility Theory scope

(Co,Cr)-codoped zinc oxide thin films (ZnO:Cr:Co) at different percentages (0%, 1–1%, 1–2%, 2–1%) were deposited on glass substrates using a chemical low-cost spray technique. The effect of Cr and Co concentration on the structural, morphological and optical properties of the ZnO:Cr:Co thin films were investigated by means of X-ray diffraction, optical measurement, contact Atomic Force Microscopy (AFM), and Photoluminescence spectroscopy. The results revealed that all films consist of single phase ZnO and were well crystallized in würtzite phase with the crystallites preferentially oriented towards (002) direction parallel to c-axis. Also, the co-doping has effective role in the enhancement of the crystallinity and leads to an improvement of roughness of the ZnO films. Doping by chrome and cobalt resulted in a slight decrease in the optical band gap energy of the films. The optical band gap of these films is calculated. The optical absorption spectra show that the absorption mechanism is a direct transition. The UV peak positions for ZnO:Cr:Co samples slightly red shift to the longer wavelength in comparison with the pure ZnO which can be attributed to the change in the acceptor level induced by the substitutional Co2+ and Cr3+ and the band-gap narrowing of ZnO with the Cr and Co dopants. The Lattice Compatibility Theory analyses have been applied in order to give original, plausible and founded explanation to the recorded preferential incorporation of cobalt ions within ZnO lattice over chromium.

Fabrication and properties of Al–P codoped p-type zinc oxide films by RF magnetron sputtering

Al–P codoped ZnO (ZnO:(Al, P)) films were grown on quartz substrate by radio frequency magnetron sputtering using mixture of argon and oxygen as sputtering gas. Types of conduction and electrical properties in ZnO:(Al, P) films were found to be dependent on oxygen partial pressure ratios in the sputtering gas mixture. When oxygen partial pressure ratio is 70 %, the codoped ZnO film had the best p-type conduction properties. It has room-temperature resistivity of 1.4 × 10−1 Ω cm, Hall mobility of 13.5 cm2/Vs and carrier concentration of 3.7 × 1018 cm−3. The p-type conduction behavior of the ZnO:(Al, P) film was confirmed by the rectifying I–V characteristics of the p-ZnO:(P, N)/n-ZnO homojunction. The phosphorus-related acceptor energy level was estimated to be located 126 meV above the valence band. Mechanism of the p-type conductivity was discussed in the present work.

First-principles calculations of electronic structure and optical properties of boron–phosphorus co-doped zinc oxide

This paper presents the electronic structure and optical properties of boron–phosphorus co-doped zinc oxide ((B, P) codoped ZnO) systems employing first principles calculations based on density functional theory. In the (B, P) codoped ZnO systems, dopants prefer to be located on the nearest-neighbor sites in the same (00l) plane forming BZn–PO complex with binding energy of −1.92eV; some hole sates appear above the valence band maximum. With increase in P concentration, P 3p states become more and more delocalized. The calculated optical properties indicate that strong optical transitions in lower energy region occur; the intensities and positions of these peaks are P concentration-dependent, which could be ascribed to the electronic transitions between P 3p and Zn 4s states. Moreover, the absorption coefficients and other optical constants of the (B, P) codoped ZnO systems, such as reflectivity, refractive index, and loss function, are also discussed.