Al:ZnO Film Research Articles

Understanding of the Relationship between the Properties of Cu(In,Ga)Se2 Solar Cells and the Structure of Ag Network Electrodes

The relation between the structure of the silver network electrodes and the properties of Cu(In,Ga)Se2 (CIGS) solar cells is systemically investigated. The Ag network electrode is deposited onto an Al:ZnO (AZO) thin film, employing a self‐forming cracked template. Precise control over the cracked template's structure is achieved through careful adjustment of temperature and humidity. The Ag network electrodes with different coverage areas and network densities are systemically applied to the CIGS solar cells. It is revealed that predominant fill factor (FF) is influenced by the figure of merit of transparent conducting electrodes, rather than sheet resistance, particularly when the coverage area falls within the range of 1.3–5%. Furthermore, a higher network density corresponds to an enhanced FF when the coverage areas of the Ag networks are similar. When utilizing a thinner AZO film, CIGS solar cells with a surface area of 1.0609 cm2 exhibit a notable performance improvement, with efficiency increasing from 10.48% to 11.63%. This enhancement is primarily attributed to the increase in FF from 45% to 65%. These findings underscore the considerable potential for reducing the thickness of the transparent conductive oxide (TCO) in CIGS modules with implications for practical applications in photovoltaic technology.

Effect of Ar-flow variation on physical properties of Al-ZnO films prepared by RF sputtering used for solar cell application

Effect of Ar-flow variation on physical properties of Al-ZnO films prepared by RF sputtering used for solar cell application

Versatile r.f. magnetron sputtering doping method to produce aluminum‐doped zinc oxide films

AbstractAluminum‐doped zinc oxide Al:ZnO (AZO) is a non‐toxic material applied as a transparent conductive oxide film. In this study, we report on the structural, optical, and electrical properties of AZO films obtained by thermally oxidizing aluminum‐doped Zn films produced by a versatile and low‐cost method of doping using the magnetron sputtering technique deposition. We use aluminum wire above the zinc target to produce Al:Zn films. The influence of r.f. power and different Al wire lengths on the AZO film properties were studied. The resulting AZO films exhibited Al concentrations of up to 2.85% and an optical gap between 3.22 and 3.29 eV. The transmittance was greater than 80% for all samples, and the electrical resistivity decreased by two orders of magnitude with Al doping. As a result, the sample with an aluminum concentration of approximately 1% had the lowest resistivity. In this work, it was possible to relate the lower resistivity with larger grain size and smaller concentrations of defects or vacancies.

Effect of calcination temperature on phase composition and optical properties of Al-ZnO nanocrystalline films

Nanocrystalline Al-ZnO films were successfully synthesized by thermal decomposition method. The method includes two stages: synthesis from the melt of organic salts and the films production. The effect of the calcination temperature varying from 600 to 800 °C on the crystallite sizes, phase composition and optical properties of the synthesized films was also investigated. X-ray diffraction (XRD) showed the formation of a hexagonal wurtzite crystal structure with a distorted lattice upon the introduction of Al3+ ions. Based on calculations and scanning electron microscopy (SEM) images, the crystallites size increased from 18 to 28 nm with the calcination temperature increasing. Optical properties of Al-ZnO films were studied by optical transmission spectra. An increase in the calcination temperature leads to a decrease in the ZnO band gap. It was shown that the proposed method makes it possible to obtain optically transparent Al-ZnO films consisting of nanocrystallites. By varying the calcination temperature, the optical properties can be adjusted, which will significantly expand the application range of these materials.

A structural, optical and electrical comparison between physical vapour deposition and slot-die deposition of Al:ZnO (AZO)

Aluminium-doped zinc oxide (AZO) is a potential low-cost alternative to indium tin oxide (ITO) for application in optoelectronic devices as a transparent conducting thin film. Typically, AZO thin films are deposited using expensive, high vacuum equipment with high energy cost and materials wastage. In this study, slot-die coating was used as an inexpensive alternative to vacuum deposition to form AZO nanoparticle thin films under ambient laboratory conditions. The films were characterised structurally, optically and electrically and compared with a commercially obtained AZO film fabricated using physical vapour deposition (PVD). Structural characterisation of the nanoparticle film shows uniform coverage across the substrate with increased crystal quality following annealing in Ar up to 500 ^{circ }C. The optical properties of the nanoparticle film exhibit a wider band gap than the PVD film, while the high density of grain boundary defects between the nanoparticles inhibits sheet conductivity.Graphical abstract

Machine learning analysis on critical structural factors of Al:ZnO (AZO) films

Machine learning (ML) has been recently approved to generalize materials design insights from many narrow-scoped individual experiments. In this study, decision tree algorithm (DT) was able to clarify critical structural factors enabling Al-doped ZnO (AZO) films with wider (or narrower) energy band gap and higher (or lower) electrical resistivity on published literature data as well as having ∼90 % average prediction accuracy. Cost-effective alternative of expensive physical models and simulations to reveal promising AZO films before physical experiments. Trained DTs were interpreted to uncover critical design insights. It was concluded that all microstructural features (crystalline size, crystallinity, dislocation density and interlamellar spacing) should be considered simultaneously through a holistic perspective in a design proposal. Al doping concentration and film thickness, as charge carrier contributors, were found as critical features for band gap and electrical resistivity, respectively. Effects on microstructural features should be considered as well as prerequisite in film design because of complex crystal growth mechanism.

Effects of Illumination and Ferroelectric Field on Nanoscale Al:ZnO Films: Implications for Nonvolatile Multistage Storage and Photosensor Devices

In this work, the nanoscale Al:ZnO (AZO) films with various densities of oxygen vacancies were grown on 0.7PbMg1/3Nb2/3O3–0.3PbTiO3 single crystal substrates. The Kelvin probe force microscopy and Hall effect were used to investigate the surface potential and carrier density modulated by the ferroelectric field and illumination effects. Tunable carrier densities and resistivity were obtained in the AZO films by changing the density of the oxygen vacancies. The carrier density can be largely modulated by the ferroelectric field effect in the AZO films with lower carrier density. The surface potential gradually increases under illumination, which can be attributed to the relaxation of the photoconductivity. As a result, the various semiconducting properties of the AZO films were achieved by the combination of ferroelectric field and illumination effect. Our results have potential applications for nonvolatile multistage storage and photosensor devices.

Comparative study of fabrication and characterization of Al-ZnO based Schottky barrier diodes using Pd and Au metal contacts

This work shows a comparative study of two types of surface barrier diodes (SBDs). RF magnetron sputtering was used to fabricate Al doped ZnO films (Al0.02Zn0.98O) at two different temperatures (100 and 300 °C) and then the structural and optical properties of these thin films were obtained and analyzed using SEM, AFM, XRD, EDX and UV–Vis spectroscopy. Then the heterojunction layers Pd/Al-ZnO/p-Si (SBD1) & Au/Al-ZnO/p-Si (SBD2) were prepared using these Al-ZnO films (developed at both the temperatures). Optical and electrical properties and the effect of temperature on ideality factor, barrier potential and carrier concentration of both the SBDs were also studied.

Gas sensing performance of Al doped ZnO thin film for H2S detection

In the present work, Al doped ZnO films have been deposited by using simple chemical Spray Pyrolysis Technique. The films were deposited at temperature 400 °C. The structural, optical, surface and electrical properties have been investigated after and before incorporation of Al. The crystalline structure of the samples was analyzed by X-ray diffraction technique (XRD). All the XRD patterns of the films showed a well-defined polycrystalline phase, fitting well with the wurtzite phase of ZnO crystal structure. The preferential growth is found to be along (002) plane i.e. c-axis. The optical properties of the ZnO and Al-ZnO films were studied using UV–Visible absorption spectroscopy. Increase in band gap is observed with the increase in doping concentration of Al. The flake like morphology for undoped and Al doped ZnO thin films were analyzed from scanning electron microscopy (SEM). The sensor response was estimated by the change in the electrical resistance of the film in the presence and absence of H2S gas. The sensor response is found to be increased with the increase in doping concentration of Al. The sensor response in relation to operating temperature and the gas concentration has been systematically studied.

Structural, optical and electrical properties of planar mixed perovskite halides/Al-doped Zinc oxide solar cells

Mixed halide perovskites CH3NH3Pb(I1−xBrx)3 thin films were successfully fabricated by spin coating using a precursor solution obtained by reacting a (1:1) molar ratio of methyl-ammonium iodide (CH3NH3I) and lead bromide (PbBr2). The films obtained by this one step process were used to fabricate a solar cell using an aluminum-doped Zinc oxide (Al–ZnO) thin film as an electron selective layer. The Al–ZnO films were fabricated by RF sputtering on indium-tin-oxide (ITO) covered glass substrates. The structural and optical properties of the films were analyzed by X-ray diffraction and ultraviolet–visible spectroscopy. The mixed halide pervoskite films were polycrystalline with an optical band gap of 1.85eV. Al–ZnO/perovskite solar cells were fabricated without a hole-selective layer by directly deposition silver (Ag) contacts on the perovskite films. The electrical properties of the cells were investigated by current–voltage (I–V) measurements. The devices showed an open circuit voltage of 0.12V, a fill factor of 0.29 and conversion efficiency of 1.6% under an illumination of 480mWcm−2. The film and cells are stable under ambient atmosphere as revealed by the absence of any changes in their color.

Structural and optical characterization of ZnO and AZO thin films: the influence of post-annealing

In the present study, ZnO and Al:ZnO (AZO) thin films were prepared by reactive RF sputtering on quartz substrates at a constant oxygen partial pressure and a typical sputtering power. Films were annealed at different temperatures in argon ambient in the oven to study their various structural and optical properties. It was understood that introducing Al into ZnO structure would affect the ZnO crystalline structure noticeably. It was observed that annealing had great influence on various properties of thin films while ZnO film showed low crystallinity, Al doping into ZnO structure pronounced significant improvement in both crystallinity and particle sizes. It was found that crystal structures, average crystalline sizes, and topology of all thin films were modified enormously by post-annealing. It was shown that films transparency fluctuated by annealing, in which the transparency of AZO thin film annealed at 500 � C was much greater than others. Annealing led to decrease optical band gap of all annealed films from 3.31 to 3.26 eV for ZnO and 4 to 3.4 eV for AZO films. Photoluminescence manifested that blue emission in as-deposited film led to two different blue and violet emissions in all AZO and ZnO films. It was identified that the emission intensity of AZO film annealed at 500 � C was 12 times more than other ZnO and AZO films.

Biodegradable Junctionless Transistors With Extremely Simple Structure

Biodegradable junctionless transistors with extremely simple structure are fabricated at room temperature. The free-standing sodium alginate membrane is used as both a substrate and a dielectric layer for the transistors. The source/drain electrodes and the channel region are made of one single patterned Al:ZnO (AZO) thin film. The proposed transistors can be operated at a low voltage of 1 V. Dissolution tests of those transistors in deionized water demonstrate their completely physical transience within 60 min. The operation mode of such transistors can effectively be tuned from the depletion mode to the enhancement mode by varying the thickness of the AZO film. Moreover, a resistor-loaded invertor was demonstrated by connecting those transistors in series with a 3 $\text{M}\Omega $ resistor.

The Optical and Electrical Properties of Al and (Al, Cu) Doped ZnO Film

The optical and electric transport properties of the Al:ZnO(AZO) and (Cu, Al):ZnO (CAZO) films deposited by pulsed laser deposition (PLD) were investigated in this paper. The experiment found the optical band gap (OBG) of AZO films at room temperature increased from 3.378eV of ZnO to 3.446eV of ZnO:Al (2min) sample, but decreased as continue add Al to ZnO:Al (4min), which were attributes to the Burstein-Moss (B-M) effect. For CAZO films, there is obvious change about hall mobility,ν, and resistivity,ρ, after doped Cu. It can be found that theνdecreased from to and theρincreased from to for AZO and CAZO, respectively, which is due to the scattering increasing between donor carriers and grain boundary as Cu2+ions increase, meanwhile, it was also found the decrease of OBG, which are very help to further understand the electric transport properties and the OBG effect of AZO-based films as well as its devices potential application.

Influence of dosing sequence and film thickness on structure and resistivity of Al-ZnO films grown by atomic layer deposition

Aluminum-doped zinc oxide (AZO) films were deposited onto amorphous silica substrates using an atomic layer deposition process with diethyl zinc (DEZ), trimethyl aluminum (TMA), and deionized water at 200 °C. Three different Al doping sequences were used at a ZnO:Al ratio of 11:1 within the films. A minimum film resistivity of 1.6 × 10−3 Ω cm was produced using sequential dosing of DEZ, TMA, DEZ, followed by H2O for the Al doping step. This “ZAZW” sequence yielded an AZO film resistivity that is independent of film thickness, crystallographic texture, and grain size, as determined by high resolution x-ray diffraction (XRD). A pseudo-Voigt analysis method yields values for grain sizes that are smaller than those calculated using other XRD methods. Anisotropic grain sizes or variations in crystallographic texture have minimal influence on film resistivity, which suggests that factors other than film texture, such as intragrain scattering, may be important in influencing film resistivity.

Nanopatterning of atomic layer deposited Al:ZnO films using electron beam lithography for waveguide applications in the NIR region

We have demonstrated the nanopatterning of atomic layer deposited (ALD) Al:ZnO (AZO) films using electron beam lithography (EBL) for plasmonic waveguide applications. The influence of grains on repeatable planar nanostructures by nanolithography process was studied for annealed films in order to avoid effects of granularity. Our results demonstrate that the nanopatterning of AZO by the EBL technique is limited due to granularity of ALD grown AZO films. This finding suggests the limitations of ALD grown samples for optical applications where nanopatterns are fabricated by the EBL technique. Furthermore, the ALD grown films lose conductivity orders of magnitude on annealing.

Transparent and conductive electrodes combining AZO and ATO thin films for enhanced light scattering and electrical performance

Al:ZnO (AZO) and Sb:SnO2 (ATO) thin films have been deposited by DC sputtering on soda lime glass (SLG) substrates. The preparation conditions were adjusted to obtain transparent films with high conductivity for AZO and high texture for ATO. Then, the combination of AZO and ATO thin films has been tested to enhance the optical scattering and the electrical performance. The structure, morphology, optical, and electrical properties have been analyzed for SLG/AZO, SLG/ATO and SLG/ATO/AZO samples. The surface texture has been characterized optically by the haze parameters for transmittance and reflectance (HT and HR), which have been related to the root mean square roughness for each sample. Some increase of the electrical resistance is obtained for the AZO films deposited on rough ATO underlayers as compared with analogous AZO grown directly on the smooth SLG substrate. Nevertheless, ATO/AZO bilayers have allowed to achieve better electrical conductivity than ATO and greater optical scattering than isolated ATO or AZO films. In this way, average haze values of HT=30% and HR=72%, together with sheet resistance of 20Ω/sq. have been obtained by combining 150nm-thick ATO and 800nm-thick AZO films.

Preparation and characterization of Al doped ZnO thin films by sol–gel process

Transparent conductive ZnO films doped with 0–5mol% of Al3+ (or AZO films) were deposited on the soda–lime glass substrates by sol–gel multilayer dip-coating. The effects of the processing conditions, especially annealing in vacuum, on the structure, optical and electrical properties of the AZO films were investigated by XRD, Raman spectroscopy, TEM and SEM, spectrophotometer, four-point prober and Hall-effect measurements. Al3+-doping led to destruction and reorganization of ZnO structure, but AZO films still had a hexagonal wurtzite structure with a preferential orientation along (002) crystal plane. After annealed in vacuum, the AZO films had better optical transmittance (>90%) and conductivity (smaller by two orders of magnitude), since annealing in vacuum promoted the growth of grains and release of residual stress, and also decreased the defects and disorder in the films. But extending the vacuum annealing time, the grains grew along other orientations except (002) crystal plane, so that the film’s square resistance became bigger. Carrier concentration (∼2.3×1019/cm3) of annealed AZO films increased with increasing Al3+ amount, but Hall mobility in the 1% Al–ZnO film was the biggest, ∼19.1cm2/Vs.

Deposition of Al doped ZnO layers with various electrical types by atomic layer deposition

AlZnO thin films with various Al/Zn composition ratios were deposited by atomic layer deposition (ALD) at 200 °C. The effect of the composition of the AlZnO films on their electrical and optical characteristics was investigated. The AlZnO films with an Al content of up to 10 at.% showed high conductivity, while further increasing in the Al content resulted in the abrupt formation of an insulating oxide film. The lowest electrical resistivity of the ALD-deposited AlZnO film was 6.5 × 10 − 4 [Ω cm] at 5 at.% Al. The AlZnO films with up to 5 at.% Al exhibited crystalline phases and a near-band-edge emission. With increasing Al content, the optical band edge showed a blue shift, and a sudden shift associated with an insulating bandgap was observed in the AlZnO films containing 20 at.% Al.

Properties of Zinc Oxide Films Cosputtered with Aluminum at Room Temperature

The electrical, structural, and optical properties of ZnO films cosputtered with Al at room temperature using a radio frequency magnetron cosputtering system were systematically investigated. The increase in carrier concentration was initially drastic with increasing cosputtered Al content and gradually alleviative for the cosputtered films behaving as an n-type degenerated semiconductor. The Hall mobility of these degenerated samples was deeply affected by both the crystal grain size and the degree of the growth orientation, becoming a dominant factor for obtaining the film with the lowest resistivity. The shifts of the ZnO(002) diffraction peak of these cosputtered films were affected by the Al3+ substitute for the lattice Zn2+ sites as well as the excess Al content existing in the interstitials. In terms of the associated optical properties, all these cosputtered films exhibited excellent transmittance around visible wavelengths. In the ultraviolet wavelengths, an apparent blue-shift at the absorption edge due to the increase in carrier concentration correlated to the Burstein–Moss shift was also observed from these degenerated cosputtered Al–ZnO films. The depth distribution of the Al impurities was more uniform than a conventional sputtered Al-doped ZnO film at a similar Al doping level. The carrier concentration and Hall mobility of the cosputtered Al–ZnO film were found to be apparently increased due to the more effective activation of the Al–O chemical bonds and less metallic Al and Zn atoms existed in the interstitials analyzed from X-ray photoelectron spectroscopy (XPS) investigations.

The structure and photoluminescence properties of Al:ZnO/porous silicon

Al:ZnO (AZO) films were deposited on porous silicon (PS) by using the rf-magnetron sputtering technique with different rf powers. The photoluminescence spectra of the samples before and after deposition of AZO were obtained, to investigate the effect of PS on the luminescence properties of AZO/PS composites. The AZO film emits blue light, due to the oxygen-related vacancies existing in the films. On the other hand, as-deposited PS emits green light. The green peak of PS shifts to the blue region after AZO deposition. Also, oxidation of Si atoms will lead to a blue shift of the emission from PS, due to the additional potential modulation with the Si nanocrystallites by a long-range Coulombic interaction of oxygen ions.