The characteristics of organic light emitting diodes with Al doped zinc oxide grown by atomic layer deposition as a transparent conductive anode

Al doped zinc oxide (AZO) films, deposited by atomic layer deposition (ALD) were investigated for applying a transparent conductive oxide (TCO) layer as an anode for organic light emitting diode (OLED) devices. AZO films with a thickness of 100 nm were deposited at various Al atomic ratios ranging from 0 to 5% at a deposition temperature (250 °C). The optimum electrical properties: the carrier mobility, the resistivity, and the sheet resistance for the 2% AZO film were found to be 16.2 cm² V^?1 s^?1, 1.5 × 10^?3 cm^?3, and 217 Ω/sq, respectively. The red OLED devices were fabricated using AZO anodes utilizing the various Al atomic ratios; the electrical and optical characteristics were then investigated. The best luminance, quantum efficiency, and current efficiency were found in the OLED device using the 2% AZO TCO; the results were 16599 cd/m², 8.2%, and 7.5 cd/A, respectively.     

Properties of multilayer gallium and aluminum doped ZnO(GZO/AZO) transparent thin films deposited by pulsed laser deposition process

Multilayer gallium and aluminum doped ZnO (GZO/AZO) films were fabricated by alternative deposition of Ga-doped zinc oxide(GZO) and Al-doped zinc oxide(AZO) thin film by using pulsed laser deposition(PLD) process. The electrical and optical properties of these GZO/AZO thin films were investigated and compared with those of GZO and AZO thin films. The GZO/AZO (1:1) thin film deposited at 400 °C shows the electrical resistivity of 4.18×10^?4 ωcm, an electron concentration of 7.5×10²⁰/cm³, and carrier mobility of 25.4 cm²/(V·s). The optical transmittances of GZO/AZO thin films are over 85%. The optical band gap energy of GZO/AZO thin films linearly decreases with increasing the Al ratio.     

A comparison of transmittance properties between ZnO∶Al films for transparent conductors for solar cells deposited by sputtering of AZO and cosputtering of AZO/ZnO

Aluminum-doped zinc oxide (AZO) thin films were deposited on sapphire (002) andglass substrates by two different sputtering techniques radio frequency magnetron cosputtering of AZO and ZnO targets and sputtering of an AZO target. The dependence of the photoluminescence (PL) and transmittance properties of the AZO films deposited by cosputtering and sputtering on the AZO/ZnO target power ratio, R and the O2/Ar flow ratio, r were investigated, respectively. Only a deep level emission peak appears in the PL spectra of cosputtered AZO films whereas both UV emission and deep level emission peaks are observed in the PL spectra of sputtered AZO films. The absorption edges in the transmittance spectra of the AZO films shift to the lower wavelength region as R and r increase. Effects ofcrystallinity, surface roughness, PL on the transmittance of the AZO films werealso explained using the X-ray diffraction (XRD), atomic force microscopy (AFM), and PL analysis results.     

Low-energy ion beam treatment of α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>(0001) and improvement of photoluminescence of ZnO thin films

A low energy N₂ ^? ion beam impinged on a α-Al₂O₃(0001) single crystal surface in the range of fluence 5×10¹⁵/cm²?1×10¹⁸/cm² at room temperature. After ion bombardment, chemical bonding on the modified sapphire surface was investigated by x-ray photoelectron spectroscopy. Below a fluence of 1×10¹⁵/cm², only a non-bonded N1s peak at the binding energy 398.7 eV was found, but further irradiation up to 2×10¹⁷/cm² induced Al?O?N bonding at around 403 eV. The occurrence of Al?N bonding was identified at ion fluence higher than 5×10¹⁷/cm² at 396.6 eV. II–VI ZnO thin films were grown on an untreated/ion-beam-induced sapphire surface by pulsed laser deposition (PLD) for the investigation of the modified-substrate effect on photoluminescence. The ZnO films grown on modified sapphire containing Al?O?N bonding only, and both Al?O?N and Al?N bonding showed a significant reduction of the peak related to deep-level defects in photoluminescence. These results are explained in terms of the formation of Al?N?O and Al?O?N layers and relaxation of the interfacial strain between Al₂O₃ and ZnO.     

Effect of substrate rotation speed on structure and properties of Al-doped ZnO thin films prepared by rf-sputtering

Al-doped ZnO (AZO) thin films were deposited on glass substrates by rf-sputtering at room temperature. The effects of substrate rotation speed (ω_S) on the morphological, structural, optical and electrical properties were investigated. SEM transversal images show that the substrate rotation produces dense columnar structures which were found to be better defined under substrate rotation. AFM images show that the surface particles of the samples formed under substrate rotation are smaller and denser than those of a stationary one, leading to smaller grain sizes. XRD results show that all films have hexagonal wurtzite structure and preferred c-axis orientation with a tensile stress along the c-axis. The average optical transmittance was above 90% in UV-Vis region. The lowest resistivity value (8.5×10^?3 Ω·cm) was achieved at ω_S=0 r/min, with a carrier concentration of 1.8×10²⁰ cm^?3, and a Hall mobility of 4.19 cm²/(V·s). For all other samples, the substrate rotation induced changes in the carrier concentration and Hall mobility which resulted in the increasing of electrical resistivity. These results indicate that the morphology, structure, optical and electrical properties of the AZO thin films are strongly affected by the substrate rotation speed.     

Composition-dependent electronic properties of indium–zinc–oxide elongated microstructures

Microrods and hierarchical structures of indium–zinc–oxide (IZO) with different compositions were grown by thermal treatments of mixtures of InN and ZnO powders. In long rods, an increase in Zn content along the growth axis is revealed by energy dispersive spectroscopy. The structures obtained range from Zn-doped indium oxide with a few atomic per cent of Zn, to IZO compounds of the type Zn_kIn₂O_k+3. X-ray photoelectron spectroscopy measurements with spatial resolution show that IZO microstructures degenerate at room temperature, with carrier concentration of the order of 10²⁰ cm^?3. Electron accumulation has been found for undoped (1 0 0) and (1 1 1) surfaces, whereas depletion of carriers at the surface is observed in IZO samples. The Fermi level position correlates with the Zn concentration at the surface which, taking into account the surface dependence of the ionization potentials, work functions and band gaps, could lead to tunable material properties for device applications. Cathodoluminescence emission intensity is enhanced by the presence of Zn, which induces spectral changes and broadening of the emission band compared with undoped material. The results are discussed in terms of the charge neutrality level and the band structure of the material.     

Structural, optical and electrical properties of N-doped ZnO thin films prepared by thermal oxidation of pulsed filtered cathodic vacuum arc deposited ZnxNy films

In this study, N-doped ZnO thin films were fabricated by oxidation of Zn_xN_y films. The Zn_xN_y thin films were deposited on glass substrates by pulsed filtered cathodic vacuum arc deposition (PFCVAD) using metallic zinc wire (99.999%) as a cathode target in pure nitrogen plasma. The influence of oxidation temperature, on the electrical, structural and optical properties of N-doped ZnO films was investigated. P-type conduction was achieved for the N-doped ZnO obtained at 450 °C by oxidation of Zn_xN_y, with a resistivity of 16.1 Ω cm, hole concentration of 2.03 × 10¹⁶ cm⁻³ and Hall mobility of 19 cm²/V s. X-ray photoelectron spectroscopy (XPS) analysis confirmed the incorporation of N into the ZnO films. X-ray diffraction (XRD) pattern showed that the films as-deposited and oxidized at 350 °C were amorphous. However, the oxidized films in air atmosphere at 450-550 °C were polycrystalline without preferential orientation. In room temperature photoluminescence (PL) spectra, an ultraviolet (UV) peak was seen for all the samples. In addition, a broad deep level emission was observed.     

Preparation and characterization of ZnO/Cu/ZnO transparent conductive films

ZnO/Cu/ZnO transparent conductive thin films were prepared by RF sputtering deposition of ZnO target and DC sputtering deposition of Cu target on n-type (001) Si and glass substrates at room temperature. The morphology, structure, optical, and electrical properties of the multilayer films were characterized by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), UV/Vis spectrophotometer, and Hall effect measurement system. The influence of Cu layer thickness and the oxygen pressure in sputtering atmosphere on the film properties were studied. ZnO/Cu/ZnO transparent conductive film fabricated in pure Ar atmosphere with 10 nm Cu layer thickness has the best performance: resistivity of 2.3×10-4 Ω·cm, carrier concentration of 6.44×1016cm-2 , mobility of 4.51cm2·(V·s)-1 , and acceptable average transmittance of 80 % in the visible range. The transmittance and conductivity of the films fabricated with oxygen are lower than those of the films fabricated without oxygen, which indicates that oxygen atmosphere does not improve the optical and electrical properties of ZnO/Cu/ ZnO films.     

Filtered vacuum arc deposition of undoped and doped ZnO thin films: Electrical, optical, and structural properties

Filtered vacuum (cathodic) arc deposition (FVAD, FCVD) of metallic and ceramic thin films at low substrate temperature (50-400 °C) is realized by magnetically directing vacuum arc produced, highly ionized, and energetic plasma beam onto substrates, obtaining high quality coatings at high deposition rates. The plasma beam is magnetically filtered to remove macroparticles that are also produced by the arc. The deposited films are usually characterized by their good optical quality and high adhesion to the substrate. Transparent and electrically conducting (TCO) thin films of ZnO, SnO₂, In₂O₃:Sn (ITO), ZnO:Al (AZO), ZnO:Ga, ZnO:Sb, ZnO:Mg and several types of zinc-stannate oxides (ZnSnO₃, Zn₂SnO₄), which could be used in solar cells, optoelectronic devices, and as gas sensors, have been successfully deposited by FVAD using pure or alloyed zinc cathodes. The oxides are obtained by operating the system with oxygen background at low pressure. Post-deposition treatment has also been applied to improve the properties of TCO films.The deposition rate of FVAD ZnO and ZnO:M thin films, where M is a doping or alloying metal, is in the range of 0.2-15 nm/s. The films are generally nonstoichiometric, polycrystalline n-type semiconductors. In most cases, ZnO films have a wurtzite structure. FVAD of p-type ZnO has also been achieved by Sb doping. The electrical conductivity of as-deposited n-type thin ZnO film is in the range 0.2-6 × 10^− 5 Ω m, carrier electron density is 10²³-2 × 10²⁶ m^− 3, and electron mobility is in the range 10-40 cm²/V s, depending on the deposition parameters: arc current, oxygen pressure, substrate bias, and substrate temperature. As the energy band gap of FVAD ZnO films is ∼ 3.3 eV and its extinction coefficient (k) in the visible and near-IR range is smaller than 0.02, the optical transmission of 500 nm thick ZnO film is ∼ 0.90.     

掺硼和掺磷的氢化纳米硅薄膜及其应用于类叠层太阳电池的研究

采用射频等离子体增强化学气相沉积法,制备了掺硼和掺磷的氢化纳米硅薄膜(nc-Si∶H),并将其应用于纳米硅薄膜类叠层太阳电池中。分析了薄膜样品的光学性能及表面形貌,结果表明:P型掺硼纳米硅薄膜的光学带隙为2.189 eV,电导率为8.01 S/cm,霍尔迁移率为0.521 cm2/(V.S),载流子浓度为9.61×1019/cm3;N型掺磷纳米硅薄膜的光学带隙为1.994 eV,电导率为1.93 S/cm,霍尔迁移率为1.694 cm2/(V.S),载流子浓度为7.113×1018/cm3;两者的晶粒尺寸都在3～5 nm之间,晶态比都在35%～45%之间,并且颗粒沉积紧密,大小比较均匀。制备了大小为20 mm×20 mm,结构为Al/AZO/p-nc-Si∶H/i-nc-Si∶H/n-nc-Si∶H/p-nc-Si∶H/i-nc-Si∶H/n-c-Si/Al背电极的纳米硅薄膜类叠层太阳电池,通过I-V曲线测试,其VOC达到544.3 mV,ISC达到85.6 mA,填充因子为65.7%。     

Preparation and characterisation of diamond-like carbon films prepared by MW ECR/PACVD process deposited on 41Cr–Al–Mo7 nitrided steel

In the present work, Diamond-Like Carbon (DLC) films were deposited by the Microwave Electron Cyclotron Resonance/Plasma-Assisted Chemical Vapour Deposition process on 41Cr–Al–Mo7 nitrided steel using a benzene–argon gas mixture. The quality of DLC films grown on nitrided steel using different deposit conditions such as benzene flow rate, temperature and time was investigated. Microstructural analysis by Raman spectroscopy showed main G-band peaks are localised between 1564 and 1595?cm^?1, while the D-band peaks are centred at 1297?cm^?1. Fourier Transform Infrared Spectroscopy showed the peaks attributed to C–H bending and stretching vibration modes are in the range of 2600–3100?cm^?1. The microstructure, surface morphology and mechanical properties of the films were examined by X-ray diffraction, atomic force microscopy and use of a Vickers indenter (Zwick). The deposition parameters of the coatings have been studied and optimised to improve mechanical properties. The observed increase in adhesion is related to the formation of (Fe,Cr)₃C, Cr₃C₂ and Cr₂₃C₆ interlayer phases. DLC films showed a better wear resistance, higher hardness and low friction coefficient compared to nitrided layers tested for comparison.     

Dual codoping for the fabrication of low resistive p-ZnO

A dual codoping method has been proposed to fabricate low resistive and stable p-ZnO thin films. Both nitrogen (N) and arsenic (As) have been used as acceptors while aluminum (Al) as donor in our dual codoping process. The As-Al-N dual codoped ZnO films have been prepared by RF magnetron sputtering on GaAs substrate using AlN doped ZnO targets (0.5, 1 and 2 mol%). In our dual codoping approach, Al and N from target and As from GaAs substrate (back diffusion) take part. X-ray diffraction (XRD), room temperature and low temperature photoluminescence (PL), electron probe micro analysis (EPMA), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM) and Hall effect measurement have been performed to investigate the effect of AlN concentration on the dual codoped ZnO films. All the films (0, 0.5 and 1 mol%) showed p-type conductivity except 2 mol% AlN doped film. The lowest room temperature resistivity, 8.6 × 10⁻² Ω cm has been achieved with a hole concentration of the order, 10²⁰ cm⁻³ for the optimum 1 mol% AlN concentration. The observed resistivity is much lower than that of monodoped (As or N) and codoped (AlN or AlAs) ZnO films. The p-type conductivity has been explained by the new complex formation mechanism.     

Thermal stability of electrical properties of ZnO:Al films deposited by room temperature magnetron sputtering

In order to investigate the thermal stability of electrical properties for aluminum doped zinc oxide (ZnO:Al, AZO) films deposited by direct current reactive magnetron sputtering, AZO films deposited from an alloy target (0.8 wt.% Al) on soda-lime glasses were annealed in argon gas at different temperatures. A data capturer was applied to monitor and collect real-time sheet resistance (R_s) of the films throughout the annealing. Results revealed that R_s of the film heated at 100 °C was reduced throughout the annealing, however, conductivity of the films annealed over 100 °C was improved at early stage but then deteriorated all along to the end. Some novel R_s change points which need more penetrations were detected. The experimental results obtained from electron diffraction spectrum, X-ray diffraction pattern, X-ray photoelectron spectrum, and Hall measurement were analyzed to explore the effect of the annealing on the electrical properties of AZO films. It was found that the exotic element, which might influence the film properties, was not observed. It was also suggested that the transformation of the crystalline structure and surface chemical bonding states, which resulted in the decrease of carrier concentration and mobility could be the reason for the conductivity degeneration of the films annealed at higher temperature.     

Effect of annealing on properties of lithium aluminum germanium phosphate electrolyte thick films prepared by aerosol deposition

Li_1.5[Al_0.5Ge_1.5(PO₄)₃] glass-ceramic powder was used for the deposition of thick films on silicon substrate by aerosol deposition. The deposited films were annealed at 873 K and 1023 K for 6 h in air. The thickness of the films was 10–12 m and the relative density was 78%–82%. As-deposited films had nano-scale grains and amorphous regions while in the annealed films, the grain growth and improved crystallinity were observed. The grain size was increased from 12 nm to 25 nm and 97 nm after annealing at 873 K and 1023 K, respectively. The ionic conductivity of the as-deposited film was 8.49 × 10^?9 S cm^?1, which increased to 1.06 × 10^?5 S cm^?1 and 1.16 × 10^?4 S cm^?1 after annealing at 873 K and 1023 K, respectively. The increased ionic conductivity is explained in terms of the increased grain size as well as the improved crystallinity.     

Photoluminescence and optical properties of nanostructure Ni doped ZnO thin films prepared by sol–gel spin coating technique

In this work, the spin coating sol–gel technique has been successfully used to deposit highly uniform and good adhesion of nano structure thin films of ZnO doped with different Ni concentrations. The morphological properties of ZnO:Ni films were studied by atomic force microscopy (AFM) technique. The surface morphology of the nanostructure films is found to depend on the concentration of Ni. The effects of Ni contents on the structural and photoluminescence (PL) properties of ZnO films were investigated. Optical constants (refractive index, n, and absorption index, k) of the undoped and Ni-doped ZnO of 0.2%, 0.4%, 0.6%, 0.8%, 1%, 3%, 5% and 7% concentrations have been obtained in the wavelength range 200–1000 nm by using spectrophotometric measurements. The dispersion parameters were determined and discussed based on the single oscillator model.     

Effects of atomic layer deposition temperatures on structural and electrical properties of ZnO films and its thin film transistors

Organic-inorganic thin film transistors (OITFTs) with Al/ZnO/PVP structure on Si substrate were fabricated and studied as to their structural and electrical properties. PVP (poly-4-vinylphenol) organic gate insulator was coated on Si substrate by spin coating method. The ZnO was deposited as an active layer by using the atomic layer deposition (ALD) method on PVP/Si substrate at various temperatures ranging from 80 to 140 °C. The structural and electrical properties of ZnO thin films were analyzed by X-ray diffraction and by hall-effect measurement system for optimum process of the OITFT. The grain size and carrier concentration of ZnO films increased, and the resistivity decreased as the deposition temperature increased from 80 to 140 °C. The field effect mobility, on/off current ratio and threshold voltage of OITFTs with ZnO active layer deposited at 100 °C were found to be 0.37 cm²/V·s, 5×10² and 5 V, respectively.     

Room temperature ferromagnetism in Mn-doped zinc oxide nanorods prepared by hybrid wet chemical route

Mn-doped (2.6-4.8 at%) aligned zinc oxide (Mn:ZnO) nanorod-films were synthesized by hybrid wet chemical route onto glass substrates. The chemical composition, structural, microstructural and magnetic studies were performed to investigate the origin of observed room temperature ferromagnetism (∼0.11 μ_B/Mn) in these Mn doped ZnO nanorod-films. XPS studies indicated that incorporated Mn was in Mn²⁺ and Mn⁴⁺ states. Mn²⁺ atomic concentration was found to be significantly larger than Mn⁴⁺ concentration in all the samples. Disappearance of the Raman peak at ∼577 cm⁻¹ arising due to the Zn interstitials may be related to the substitution of Mn²⁺ in the Zn²⁺ site with annealing. Thus, Mn metal inclusions as Mn²⁺ in the ZnO lattice are possibly responsible for such large magnetic moment in the films.     

High rate reactive magnetron sputtering of ZnO:Al films from rotating metallic targets

Aluminum doped zinc oxide (ZnO:Al) films were reactively sputtered at a high discharge power from dual rotating metallic targets (Zn:Al = 99.5:0.5 wt.%). Deposition conditions like substrate temperature and working points were varied in order to prepare high quality ZnO:Al films. The influences on electrical and optical ZnO:Al thin film properties and surface texture before and after chemical etching in diluted HCl were studied in order to achieve light scattering films as front contact for solar cells. High dynamic deposition rate close to 90 nm m/min and high Hall mobility of up to 47 cm²/Vs were obtained. Transmission of more than 85% in the visible spectral range is obtained for all ZnO:Al films in this study. In addition, the absorption in near infrared region is low due to low doping. Surface texture after etching is usually much rougher than before. However, some films reveal after etching small surface features that are similar to initial surface features. We propose a relationship between initial and post-etched surface textures.     

Zn靶与掺铝ZnO靶共溅射制备ZnO:Al薄膜及其性能

采用Zn靶和ZnO(掺2%Al2O3(质量分数))陶瓷靶在玻璃衬底上共溅射沉积Al掺杂ZnO薄膜,即ZnO:Al透明导电薄膜,研究Zn靶溅射功率(0～90 W)和衬底温度(室温、100℃和200℃)对薄膜结构、形貌、光学和电学性能的影响。结果表明:按双靶共溅射工艺制备的ZnO:Al薄膜的晶体结构均为六角纤锌矿结构,且随着Zn靶溅射功率的增加,薄膜的结晶质量呈现出先改善后变差的规律,薄膜中的载流子浓度逐渐升高,电阻率逐渐降低,而薄膜的光学性能受其影响不大;随着衬底温度的升高,薄膜的结晶性能得到改善,薄膜的可见光透过率增强,电阻率降低。     

Photoluminescence behavior and visible light photocatalytic activity of ZnO,ZnO/ZnS and ZnO/ZnS/α-Fe2O3 nanocomposites

In order to achieve effective, economic, and easily achievable photocatalyst for the degradation of dye methyl orange (MeO), ZnO, ZnO/ZnS and ZnO/ZnS/α-Fe₂O₃ nanocomposites were prepared by simple chemical synthetic route in the aqueous medium. Phase, crystallinity, surface structure and surface behavior of the synthesized materials were determined by X-ray diffraction (XRD) and Brunauer–Emmett–Teller analysis (BET) techniques. XRD study established formation of good crystalline ZnO, ZnO/ZnS and ZnO/ZnS/α-Fe₂O₃ nanomaterials. By using intensity of constituent peaks in the XRD pattern, the compositions of nanocomposites were determined. From the BET analysis, the prepared materials show mesoporous behavior, type IV curves along with H4 hysteresis. The ZnO/ZnS/α-Fe₂O₃ composite shows the largest surface area among three materials. From the UV–visible spectra, the band gap energy of the materials was determined. Photoluminescence spectra (PL) were used to determine the emission behavior and surface defects in the materials. In PL spectra, the intensity of UV peak of ZnO/ZnS is lowered than that of ZnO while in case of ZnO/ZnS/α-Fe₂O₃, the intensity further decreased. The visible emission spectra of ZnO/ZnS increased compared with ZnO while in ZnO/ZnS/α-Fe₂O₃ it is further increased compared with ZnO/ZnS. The as-synthesized materials were used as photocatalysts for the degradation of dye MeO. The photo-degradation data revealed that the ZnO/ZnS/α-Fe₂O₃ is the best photocatalyst among three specimens for the degradation of dye MeO. The decrease of intensity of UV emission peak and the increase of intensity of visible emission cause the decrease of recombination of electrons and holes which are ultimately responsible for the highest photocatalytic activity of ZnO/ZnS/α-Fe₂O₃.