Nitrogen-doped ZnO Thin Films Research Articles

Effect of concentration on the properties of nitrogen-doped zinc oxide thin films grown by electrodeposition

Zinc oxide is one of the most researched semiconductors owing to the outstanding properties that make it useful in various industrial applications, such as solar cells and other optoelectronics. In this work, ZnO thin films were prepared in five different concentrations and doped with four nitrogen atoms from triethylene tetramine (TETA) to fabricate a ZnO for optoelectronic applications using an electrodeposition technique. The doped ZnO thin films were synthesized and deposited on ITO glass substrates. The deposited thin films were annealed at 400°Cfor 60min in a furnace under the same conditions. The thin films' optical, electrical, and surface morphological properties were characterized using UV–Vis Spectrophotometer, Four Point Probe (FPP), and Scanning Electron Microscope (SEM), respectively. The optical properties confirmed the film's suitability for various transparent device applications with a high optical transmittance of about 90% at the wavelength between 250 and 950 nm. The optical band gaps of 3.25 eV to 3.50 eV were obtained at ZnO concentrations from 0.2 M to 1.0 M. The SEM images depicted a polycrystalline nature of the films with irregular nanoparticle shapes across the substrates. Electrical results established the high conductivity of nitrogen-doped ZnO thin films, thereby making the thin films suitable as transparent conducting oxides for devices such as solar cells and optoelectronics.

Investigation of the Effects of Rapid Thermal Annealing on the Electron Transport Mechanism in Nitrogen-Doped ZnO Thin Films Grown by RF Magnetron Sputtering.

Nitrogen-doped ZnO (ZnO:N) thin films, deposited on Si(100) substrates by RF magnetron sputtering in a gas mixture of argon, oxygen, and nitrogen at different ratios followed by Rapid Thermal Annealing (RTA) at 400 °C and 550 °C, were studied in the present work. Raman and photoluminescence spectroscopic analyses showed that introduction of N into the ZnO matrix generated defects related to oxygen and zinc vacancies and interstitials. These defects were deep levels which contributed to the electron transport properties of the ZnO:N films, studied by analyzing the current–voltage characteristics of metal–insulator–semiconductor structures with ZnO:N films, measured at 298 and 77 K. At the appliedtechnological conditions of deposition and subsequent RTA at 400 °C n-type ZnO:N films were formed, while RTA at 550 °C transformed the n-ZnO:N films to p-ZnO:N ones. The charge transport in both types of ZnO:N films was carried out via deep levels in the ZnO energy gap. The density of the deep levels was in the order of 1019 cm−3. In the temperature range of 77–298 K, the electron transport mechanism in the ZnO:N films was predominantly intertrap tunneling, but thermally activated hopping also took place.

Investigation of nitrogen doped ZnO thin films: Effects on their structural and optical properties

Un-doped and nitrogen-doped ZnO thin films were grown by using radio frequency (RF) magnetron sputtering method changing the nitrogen flow rate between 0% −12.5% and the thickness dependence of films was determined. The effect of nitrogen doping concentration on the structural, morphological, and optical properties of zinc oxide thin films was studied. X-ray diffraction (XRD) analysis confirmed that the nitrogen-doped ZnO films belong to the hexagonal crystal structure. The optical properties of the grown samples were examined by optical spectrophotometer and spectroscopic ellipsometer. Transmittance spectra were obtained by spectrophotometer measurements and the effect of nitrogen ratio was investigated. It has been observed that as the nitrogen ratio increases, the transmittance decreases up to ∼500 nm and then increases. By using the transmittance curve, the energy band gap was calculated. Further detailed optical analysis was made by the spectroscopic ellipsometry technique. Fitting was performed to ensure the agreement between the experimentally obtained Ψ values and theoretically determined Ψ values using the Cauchy model. As a result, the refractive index was found for each film and it was observed that the refractive index decreased as the nitrogen ratio increased. The scanning electron microscopy (SEM) measurements showed that the surface morphology of the films changes with N doping. Nitrogen was observed in Fourier transform infrared spectra analysis. 5% nitrogen-doped ZnO films were grown on the glass substrate using RF magnetron sputtering at room temperature. Samples are prepared by varying thicknesses during the deposition process. XRD and SEM measurements of the samples show the variation in the crystal structure and surface morphology of the film with varying thicknesses. All the samples are tested for the transmittance and band gap. The increase of film thickness increases the grain size. The transmittance is influenced by the film thickness. • Un-doped and nitrogen doped ZnO thin films were grown by using RF magnetron sputtering method. • The band gap values were changed by changing N doping. • The refractive index values of ZnO films decrease with the introduction of nitrogen into the structure. • The band gaps decreased from 3.25 eV to 3.20 eV as the thickness increased. • Zn–N bonds were attributed at ∼1380 and ∼1502 cm −1 .

Columnar nitrogen-doped ZnO nanostructured thin films obtained through atomic layer deposition

The present study was aimed to develop nitrogen-doped nanostructured ZnO thin films. These films were produced in a sequential procedure involving the atomic layer deposition technique, and a hydrothermal process supported by microwave heating. Employing the atomic layer deposition technique, through self-limited reactions of diethylzinc (DEZn) and H2O, carried out at 3.29 × 10−4 atm and 190 °C, a high-quality ZnO seed was grown on a Si (100) substrate, producing a textured film. In a second stage, columnar ZnO nanostructures were grown perpendicularly oriented to the silicon substrate on those films, using a solvothermal process in a microwave heating facility, employing Zn(NO3)2 as zinc precursor, while hexamethylenetetramine (HMTA) was used to produce the bridging of Zn2+ ions. The consequence of N-doping concentration on the physicochemical properties of ZnO thin films was studied. The manufactured films were structurally analyzed by scanning electron microscopy and x-ray diffraction. Also, x-ray photoelectron spectroscopy, Raman, and UV–vis spectroscopies were used to provide further insight on the effect of nitrogen doping. The N-doped films displayed textured wurtzite-like structures that changes their preferential growth from the (002) to the (100) crystallographic plane, apparently promoted by the increase of nitrogen precursor. It is also shown that nitrogen-doped films undergo a reduction in their bandgap, compared to ZnO. The methodology presented here provides a viable way to perform high-quality N-ZnO nanostructured thin films.

Impact of defect sites on the Raman scattering properties of nitrogen doped ZnO thin films

This paper focuses on the influence of nitrogen doping and vacuum annealing on the properties of nitrogen-doped ZnO thin films grown by spin coating technique. The optical absorption study was indirect evidence for the presence of intrinsic defects like oxygen vacancy and Zn interstitials and in line with this, Urbach energy was calculated to confirm the disorder levels. Using Urbach energy, the electron–phonon interaction strength was evaluated and its impact on the line shape of major Raman mode (E2) was studied in detail. Apart from these, possible reasons for peak shift, anisotropic broadening and asymmetry line shape behaviour are detailed here.

Effect of doping concentration and annealing temperature on nitrogen-doped ZnO thin films: an investigation through spectroscopic techniques

Undoped and nitrogen-doped ZnO (NZO) thin films were deposited by sol–gel spin-coating technique on glass substrates. The thin film preparation was accomplished using zinc acetate dihydrate, monoethanolamine and 2-methoxyethanol as the precursors. Ammonium acetate was used as the source of nitrogen for doping. The effect of dopants and the post-heating temperature on the various physical properties of the deposited films was explored. The X-ray diffraction studies reveal the polycrystalline nature of the films which possess a preferred c-axis orientation. Raman characterizations of the films show a clear indication of nitrogen incorporation in the films. The carrier concentration of the thin films was of the order of 1017/cm3 and resistivity as minimum as 0.371 Ω cm was observed for 1 at.% NZO thin films post-heated at 500 °C. The 1 at.% and 2 at.% doped NZO films post-heated at 300 °C and 1 at.%, 2 at.% and 3 at.% doped NZO films with post-heat treatment at 500 °C exhibited p-type conductivity. In the aging study, 500 °C annealed films retained p-type conductivity for 5 days.

Influence of high nitrogen doping on optical properties of ZnO thin films

ZnO semiconductor is one of the photocatalyst materials that has become a concern in the world of research. This is due to its ability to degrade pollutants effectively, economically and environmentally friendly. Many studies have been developed to enhance the photocatalytic activity of ZnO, one of them by the addition of doping. Increasing the concentration of non-metallic doping on ZnO will affect its energy level so that it can improve the physical properties and optical properties. Nitrogen has been considered as a very good dopant because it has an ionic radius comparable to oxygen and also has small ionization energy. High nitrogen-doped ZnO thin films have been deposited by sol-gel spray coating methods on glass substrate. Using spectrophotometer UV-Vis Materials were characterized to obtain the absorbance spectrum, in order to analyze its optical absorption region. The result shows that all materials have high absorption in the UV region. In general, the graph shows that the absorption spectra in the UV region increase with increasing percentage of dopant and have maximum absorption spectra on the sample with 40% dopant. It indicates that high N-doping enhanced the light absorption capacity of ZnO.

Passivation Mechanism of Nitrogen in ZnO under Different Oxygen Ambience

Nitrogen-doped ZnO thin films were grown on a-plane Al2O3 by plasma-assisted molecular beam epitaxy. Hall-effect measurements indicated that the nitrogen-doped ZnO films showed p-type behavior first, then n-type, with the growth conditions changing from oxygen-radical-rich to oxygen-radical-deficient ambience, accompanied with the increase of the N/O ratio in the plasmas. The increasing green emission in the low temperature photoluminescence spectra, related to single ionized oxygen vacancy in ZnO, was ascribed to the decrease of active oxygen atoms in the precursor plasmas. CN complex, a donor defect with low formation energy, was demonstrated to be easily introduced into ZnO under O-radical-deficient ambience, which compensated the nitrogen-related acceptor, along with the oxygen vacancy.

Effect of surface carbon contamination on the chemical states of N-doped ZnO thin films

Nitrogen-doped ZnO thin films [ZnO:N] and intentional surface carbon-contaminated ZnO:N thin films [ZnO:N@C] were grown on quartz substrates by radio frequency magnetron sputtering deposition method. The structural, electrical and optical properties as well as chemical states of elements were investigated by means of X-ray diffraction (XRD), Hall effect measurement (Hall), UV–Vis–Near infrared spectrophotometer and X-ray photoelectron spectroscopy (XPS). The results indicate that surface carbon contamination almost does not affect the band gap of ZnO:N thin films but has a strong impact on the crystal quality of ZnO:N thin film surface and results in a significant increase in tensile stress. The XPS analysis shows that the effect of surface carbon contamination treatment on the chemical states of ZnO:N thin films is remarkable. Because the stability of Zn–N bonds in N-rich local environments is nowhere near that of those in O-rich local environments, the N atoms in N-rich local environments easily bond with surface carbon atoms to form undesirable C–N bonds, thus resulting in a decrease of NO acceptors in N-rich local environments. Obviously, it is unfavorable to subsequently prepare high stability of N-doped p-type ZnO thin films.

High visible light photocatalytic activity of nitrogen-doped ZnO thin films deposited by HiPIMS

Reactive High Power Impulse Magnetron Sputtering (HiPIMS) of a pure Zn target in Ar/N2/O2 gas mixture was used to synthesize ZnOxNy thin films with nitrogen content and optical band-gap energy values ranging over 0–6.2at.% and 3.34–1.67eV, respectively. The fine control of the nitrogen content in the deposited ZnOxNy thin films composition was possible through the stabilization of the reactive HiPIMS discharge in the transition region, between the metallic and compound target sputtering modes. Various analytical techniques such as AFM, XPS, XRD, UV–Vis and Raman spectroscopy have been employed to characterize the properties of the deposited thin films. The photocatalytic activity, light excitation efficiency and life time of photo-generated charge carriers in the ZnOxNy films were investigated by photo-electrochemical and photo-current measurements during visible light on/off irradiation cycles. The as-deposited films showed poor visible-light photocatalytic activity and photo-current response. Post-deposition annealing of the films in nitrogen atmosphere resulted in a slight enhancement of crystalline order. However, the thermal treatment improved considerably the film photocatalytic activity and stability for water splitting under visible light irradiation. The optimum photo-current response and photocatalytic activity have been obtained for the annealed ZnOxNy films with a nitrogen content of 3.4at.% (photon-to-current efficiency up to 33% at λ=370nm and 0.5V biasing potential vs. Ag/AgCl). Increasing the nitrogen content above this value, in spite of lowering the energy band-gap, worsened the visible light photocatalytic activity of the films due to deterioration of the crystalline order.

Friction and wear behavior of nitrogen-doped ZnO thin films deposited via MOCVD under dry contact

Most researches on doped ZnO thin films are tilted toward their applications in optoelectronics and semiconductor devices. Research on their tribological properties is still unfolding. In this work, nitrogen-doped ZnO thin films were deposited on 304 L stainless steel substrate from a combination of zinc acetate and ammonium acetate precursor by MOCVD technique. Compositional and structural studies of the films were done using Rutherford Backscattering Spectroscopy (RBS) and X-ray Diffraction (XRD). The frictional behavior of the thin film coatings was evaluated using a ball-on-flat configuration in reciprocating sliding under dry contact condition. After friction test, the flat and ball counter-face surfaces were examined to assess the wear dimension and failure mechanism. Both friction behavior and wear (in the ball counter-face) were observed to be dependent on the crystallinity and thickness of the thin film coatings.

Effect of doping concentration on the conductivity and optical properties of p-type ZnO thin films

Nitrogen doped ZnO (NZO) thin films were synthesized on glass substrates by the sol–gel and spin coating method. Zinc acetate dihydrates and ammonium acetate were used as precursors for zinc and nitrogen, respectively. X-ray diffraction study showed that the thin films have a hexagonal wurtzite structure corresponding (002) peak for undoped and doped ZnO thin films. The transmittance of the films was above 80% and the band gap of the film varies from 3.21±0.03eV for undoped and doped ZnO. The minimum resistivity of NZO thin films was obtained as 0.473Ωcm for the 4at% of nitrogen (N) doping with a mobility of 1.995cm2/Vs. The NZO thin films showed p-type conductivity at 2 and 3at% of N doping. The AC conductivity measurements that were carried out in the frequency range 10kHz to 0.1MHz showed localized conduction in the NZO thin films. These highly transparent ZnO films can be used as a possible window layer in solar cells.

Transition from diamagnetic to ferromagnetic state in laser ablated nitrogen doped ZnO thin films

Transition from room temperature diamagnetic to ferromagnetic state in N doped ZnO (ZnO:N) films grown by pulsed laser deposition with tunable energy density has been identified. ZnO:N films deposited with moderate laser energy density of 2.5 J/cm2 are single phase and nearly defect free having N dopant substitution at O sites in ZnO lattice, exhibiting intrinsic ferromagnetism. When energy density reduces (<2.5 J/cm2), defects in ZnO:N film degrades ferromagnetism and exhibit diamagnetic phase when grown at energy density of 1.0 J/cm2. Growth kinetics, which in turn depends on laser energy density is playing important role in making transition from ferromagnetic to diamagnetic in ZnO:N films.

Structure and Optical Properties of ZnO:N Films Doped with Nitrogen Atoms

s: In this study, nitrogen-doped ZnO thin films with different nitrogen content were produced by a wet chemical process. The optical properties and the structure of these ZnO films were investigated by LT-PL spectrum, Raman spectrum, SEM and XRD. XRD result showed that the cubic ZnO phase appeared in the 10% nitrogen-doped ZnO films, which might be attributed to the stress in these ZnO film. Moreover, results of SEM measurement proved that the nitrogen atoms were introduced into the lattice of nanoZnO crystal. In addition, LT-PL spectra also confirmed that this new appeared phase was a cubic ZnO phase, due to the lack of the new PL mission peak. Key words: ZnO, wet chemical method, luminescence, XRD

Structural, linear, and nonlinear optical properties of radio frequency-sputtered nitrogen-doped ZnO thin films studied using z-scan technique

The third-order nonlinear optical properties of undoped and nitrogen-doped ZnO thin films were evaluated using the z-scan technique. The films were sputter-deposited on glass substrates using radio frequency power. The He–Ne continuous wave laser operating at 633 nm was used as an irradiation source. A change in the growth mode in the nitrogen-doped films was observed. The grain size and roughness were found to be dependent on the nitrogen concentration, as shown by atomic force microscopy analysis. The optical band gap was determined and found to increase with nitrogen concentration in the films. Both nonlinear absorption and refraction nonlinearities were exhibited by the deposited films. The nonlinear refractive index n2, the nonlinear absorption coefficient βeff and the third-order nonlinear optical susceptibility χ(3) were determined and found to be largest. Multiple diffraction ring patterns were observed when the samples were made to interact with the laser beam and were attributed to refractive index change and thermal lensing. Further, optical power-limiting experiments were performed to determine the optical-limiting threshold and clamping values for undoped and nitrogen-doped ZnO films.

Growth, structural and optoelectronic properties tuning of nitrogen-doped ZnO thin films synthesized by means of reactive pulsed laser deposition

Pulsed laser deposition has been successfully used to achieve in-situ nitrogen doping of zinc oxide thin films at a temperature as low as 300°C. Nitrogen-doped zinc oxide (ZnO:N) thin films with a maximum nitrogen content of 0.7at.% were obtained by varying the nitrogen background pressure in the range of 0–150mTorr. The ZnO:N thin films were found to present hexagonal crystalline structure with dense and smooth surface. X-ray photoelectron spectroscopy analysis confirms the effective incorporation of nitrogen into ZnO thin films. Optical transmission together with room temperature photoluminescence measurements show that the band gap of the ZnO:N films shifts from 3.3eV to 3.1eV as nitrogen concentration varies in the range of 0.2–0.7at.%. The narrower band gap is obtained at an optimal nitrogen concentration of 0.22at.%. This band gap narrowing is found to be caused by both nitrogen incorporation and nitrogen-induced defects in the ZnO:N films.

Structural and electrical properties of nitrogen-doped ZnO thin films

ZnO and nitrogen-doped ZnO thin films were prepared onto glass substrate by pulsed filtered cathodic vacuum arc deposition (PFCVAD) system at room temperature. The influence of doping on the structural, electrical and optical properties of thin films was investigated. XRD studies were carried out to analyze and compare the structural quality of undoped and nitrogen-doped ZnO films. Raman measurement was performed to study the doping effects in the ZnO. The optical transmittances of all films are studied as a function of wavelength using UV–VIS–NIR spectrophotometer. The optical band gap values of the films are found using absorbance spectrums. The electrical studies for the films are carried out by using Hall-effect measurements.

硼对氮掺杂的p型ZnO薄膜的影响

A stable and repeatable p-type ZnO is the key to realize the practical applications of photoelectric devices. Nitrogen has been considered as a possible acceptor dopant for p-type ZnO for a long time. However, the low solubility of nitrogen acceptor at oxygen site in ZnO is considered to be one of the main obstacles for p-type ZnO. In this paper, B/N co-doped p-type ZnO thin films were grown on sapphire substrate by plasma-assisted molecular beam epitaxy. The effect of boron on the nitrogen doping was studied by comparing with the single nitrogen doped thin films. X-ray photoelectron spectroscopy demonstrated there exists boron and B-N bond in the ZnO thin film. Compared to the single N-doped sample, B/N codoped samples present much higher carrier density. And the ZnO:(B, N) thin films show stable p-type conduction in two years. It is attributed to the increase of solubility of nitrogen acceptor. It benefits from the strong B-N bonding and weak donor character of boron at zinc site. Boron will not bring strong compensation for acceptors. It suggests that boron is a good co-doping candidate for nitrogen doped ZnO thin films.

N-doped ZnO thin film for development of magnetic field sensor based on surface plasmon resonance

Magnetic-field-dependent optical properties of nitrogen-doped ZnO (ZnO:N) thin films were investigated using surface plasmon resonance (SPR) and a highly sensitive (4.65/Tesla) magnetic field sensor has been realized. The refractive index (RI) of ZnO:N film increases from 1.949 to 2.025 with increase in N doping from 0% to 10% demonstrating tunable RI. In contrast to pure ZnO, SPR curves for ZnO:N films exhibit a shift toward lower angles with increasing applied magnetic field from 0 to 35mT due to change in reflectance of light upon reflection from ferromagnetic surface. Results indicate promising application of ferromagnetic ZnO:N film as a magnetic field sensor.

Fabrication of Tantalum and Nitrogen Codoped ZnO (Ta, N-ZnO) Thin Films Using the Electrospay: Twin Applications as an Excellent Transparent Electrode and a Field Emitter

The realization of stable p-type nitrogen-doped ZnO thin films with durable and controlled growth is important for the fabrication of nanoscale electronic and optoelectronic devices. ZnO thin films codoped with tantalum and nitrogen (Ta, N-ZnO) were fabricated by using the electrospraying method at an atmospheric pressure. X-ray diffraction (XRD) studies demonstrated that all the prepared films were polycrystalline in nature with hexagonal wurtzite structure. In addition, a shift in the XRD patterns was observed, and the crystal orientation was changed at a certain amount of nitrogen (>6 at.%) in the starting solution. Analysis of X-ray diffraction patterns and X-ray photoelectron spectra revealed that nitrogen which was combined with the zinc atom (N-Zn) was successfully doped into the ZnO crystal lattice. It was also observed that 2 at.% tantalum and 6 at.% nitrogen (2 at.% Ta and 6 at.% N) were the optimal dopant amounts to achieve the minimum resistivity of about 9.70 × 10(-5) Ω cm and the maximum transmittance of 98% in the visible region. Consequently, the field-emission characteristics of such a Ta, N-ZnO emitter can exhibit the higher current density of 1.33 mA cm(-2), larger field-enhancement factor (β) of 4706, lower turn-on field of 2.6 V μm(-1), and lower threshold field of 3.5 V μm(-1) attributed to the enhanced conductivity and better crystallinity of films. Moreover, the obtained values of resistivity were closest to the lowest resistivity values among the doped ZnO films as well as to the indium tin oxide (ITO) resistivity values that were previously studied. We confirmed that the tantalum and nitrogen atoms substitution in the ZnO lattice induced positive effects in terms of enhancing the free carrier concentration which will further improve the electrical, optical, and field-emission properties. The proposed electrospraying method was well suitable for the fabrication of Ta, N-ZnO thin films at optimum conditions with superior electrical, optical, and field-emission characteristics, implying the potential applications as both a transparent electrode and field-emission (FE) devices.