Gallium-doped Zinc Oxide Research Articles

Aerosol-assisted route to low-E transparent conductive gallium-doped zinc oxide coatings from pre-organized and halogen-free precursor.

Thermal control in low-emission windows is achieved by the application of glazings, which are simultaneously optically transparent in the visible and reflective in the near-infrared (IR). This phenomenon is characteristic of coatings with wide optical band gaps that have high enough charge carrier concentrations for the material to interact with electromagnetic radiation in the IR region. While conventional low-E coatings are composed of sandwiched structures of oxides and thin Ag films or of fluorinated SnO2 coatings, ZnO-based glazing offers an environmentally stable and economical alternative with competitive optoelectronic properties. In this work, gallium-doped zinc oxide (GZO) coatings with properties for low-E coatings that exceed industrial standards (Tvisible > 82%; R2500 nm > 90%; λ(plasma) = 1290 nm; ρ = 4.7 × 10−4 Ω cm; Rsh = 9.4 Ω·□−1) are deposited through a sustainable and environmentally friendly halogen-free deposition route from [Ga(acac)3] and a pre-organized zinc oxide precursor [EtZnOiPr]4 (1) via single-pot aerosol-assisted chemical vapor deposition. GZO films are highly (002)-textured, smooth and compact without need of epitaxial growth. The method herein describes the synthesis of coatings with opto-electronic properties commonly achievable only through high-vacuum methods, and provides an alternative to the use of pyrophoric ZnEt2 and halogenated SnO2 coatings currently used in low-emission glazing and photovoltaic technology.

Effect of Annealing on the Current-Voltage Characteristics of the Ag/GaZnO/FTO Structure

Using the method of electron beam evaporation, the conductive films of gallium doped (1.6 at%) zinc oxide (GZO) were obtained. As the upper and lower electrodes, silver and glass substrates coated with tin oxide doped with fluorine (FTO) were used, respectively. The films were annealed in air at 350°C for 1 hour. The current-voltage characteristics of the Ag/GZO/FTO structure reveal a linear behavior. Annealing of the entire structure of Ag/GZO/FTO under the same conditions results in a change in the behavior of the current-voltage characteristic from ohmic to the diode with the Schottky barrier. Using the theory of thermionic emission, the methods of Cheung and Norde, the current-voltage characteristics of forward bias are analyzed and the values of ideality factor, the Schottky barrier height, and series resistance are determined.

Preparation and thermochromic behaviors of polydiacetylene/indium or gallium doped zinc oxide nanocomposites

Polydiacetylene (PDA) is one of the well-known thermochromic materials having a high potential in applications such as displays and sensor technology. Many research groups have been working on controlling thermochromic reversibility of PDA-based materials. In this research, the colorimetric response of PDA assembled with indium or gallium doped zinc oxide was studied with various concentrations. Indium or gallium doped zinc oxide was prepared by hydrothermal method. The compositions of 5, 10, and 15% of indium and 5, 12, and 24% gallium, respectively. Undoped zinc oxide and gallium doped zinc oxide exhibited the nanoflowers composed of nanosheets while the indium doped zinc oxide showed the nanorod structure and combined to be nanoflowers. Monomer of PDA composing 10, 12-pentacosadiynoic acid in ethanol was mixed with indium and gallium doped zinc oxide precursor solution at 20% weight. Ultra-violet light source was used to photo-polymerize for five minutes after incubation at low temperature for a prolong cooling. For nanocomposites of poly(PCDA) and undoped and gallium doped zinc oxide, the color of nanocomposite changed from blue to light-purple at above 70°C and the color can be reversible when cooling down to room temperature. However, for nanocomposites of PCDA and indium doped zinc oxide, the color change from blue to light-purple at above 50°C then become red than those in gallium doped PDA nanocomposite. In addition, the color of PCDA nanocomposite with indium doped zinc oxide cannot be reversible back to the original color.

Optimization of Gallium concentration to improve the performance of ZnO nanopowders for nanophotonic applications

This study reports the effects of gallium concentration on the properties of doped zinc oxide nanopowders. Both pure and gallium doped zinc oxide (GZO) nanoparticles were prepared via a simple and effective sol-gel method. The structural, morphological and optical properties of synthesized GZO nanopowders were investigated using different characterization methods such as X-ray diffraction, Raman, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometer, UV–Vis diffuse reflectance spectroscopy, Transmission electron microscopy, Photoluminescence spectroscopy, X-ray and ion-beam-induced luminescence (IBIL) measurements. Firstly, in the presence of Ga ions in the host the purity of synthesized sample was evaluated by X-ray diffraction analysis. X-ray photoelectron spectroscopy confirmed the presence of bonding states of Zn, O, and Ga on the surface of powders. Raman spectroscopy analysis showed that the increase of Ga content upper than 1 at.% leads to an increase in the number of defects in the ZnO lattice. Field emission scanning electron microscopy (FESEM) confirmed that the uniform integration of spherical and hexagonal rod shape particles can be found in the doped samples. According to FESEM images, the particle size of prepared nanopowders increased from 101 to 200 nm by increasing in the Ga doping concentration. The photoluminescence, X-ray and ion beam induced luminescence results of the pure and doped ZnO powders revealed novel blue-green emission band from 400 up to 550 nm at room temperature. Optical and structural studies confirmed the optimized Ga concentration is 1 at.%.

Enhancement of Electrical Conductivity of Transparent Ga -Doped Zinc Oxide Films via Quench Reduction in an Atmospheric Pressure Plasma Jet

Transparent conducting oxides such as gallium-doped zinc oxide (GZO) are of increasing importance for displays and photovoltaic applications. For manufacturing, an atmospheric-pressure plasma jet (with no vacuum chamber) is suitable for continuous inline processing; however, deposition becomes more susceptible to oxygen quenching, reducing the plasma's reactivity and the formation of oxide. Here the authors show that the electrical conductivity and deposition rate of GZO films are both enhanced by using a different nozzle feature, to lessen oxygen quenching. These findings may be extended to other areas where vacuum-based technologies are not applicable, such as biomedical applications.

Transparent conductive oxides for the epsilon-near-zero Tamm plasmon polaritons

We demonstrate the possibility of using transparent conducting oxides [aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), indium tin oxide (ITO)] to form Tamm plasmon polaritons in the near-infrared spectral range where the permittivity of oxides is near zero. The spectral properties of the structures are investigated in the framework of the temporal coupled-mode theory and confirmed by the transfer matrix method. It is found that in the critical coupling conditions, the maximal $ Q $Q-factor of a Tamm plasmon polariton is achieved when a photonic crystal is conjugated with the AZO film, while at the conjugation with the ITO films, the broadest spectral line is obtained. The sensitivity of the wavelength and spectral width of the Tamm plasmon polariton to changes in the oxide film thickness, bulk concentration of a dopant, and angle of incidence is demonstrated.

Elucidation of structural, morphological, optical and photoluminescence properties of single and (In, Ga) co-doped ZnO nanocrystalline thin films

Single and co-doped ZnO thin films are currently under intense investigation and development for optoelectronic applications. Here in this study, pristine, indium-doped (IZO), gallium-doped (GZO) and co-doped (IGZO) ZnO thin films were deposited on a glass substrate using radio frequency magnetron sputtering. A comparative study of all the films was carried out on the basis of their various properties. The effect of single and co-doping on the structural (X-ray diffraction (XRD) studies and Raman studies), morphological (field emission scanning electron microscopy and energy dispersive X-ray spectroscopy studies) and optical properties (ultraviolet–visible (UV–Vis) and photoluminescence (PL)) of the deposited films was investigated. X-ray photoelectron spectroscopy (XPS) characterization was employed to analyse the surface chemical composition and bonding of the deposited film. From the XRD patterns, it was found that the films were highly crystalline in nature and preferentially oriented along the (002) direction with a hexagonal wurtzite structure, consistent with Raman analysis. IGZO films displayed a dramatic improvement in the surface morphology as compared with the single dopant films due to the compensation effect of gallium and indium doping which reduced the lattice strain. The XPS analysis confirmed the presence of the oxidized dopants in each film. All thin films have shown excellent optical properties with more than 90% transmission in the visible range of light. The blue-shift of the absorption edge accompanied by the increase of the optical band gap confirmed the Burstein–Moss effect. The UV PL peak originated from the near band edge emission of crystalline ZnO, while the visible PL was associated with the radiative transition related to oxygen interstitial (Oi) defects in the ZnO structure.

Efficient Alpha Radiation Detector using Low Temperature Hydrothermally Grown ZnO:Ga Nanorod Scintillator

We report efficient detection of alpha radiation on highly textured and vertically aligned along (002) Gallium-doped Zinc Oxide (ZnO:Ga) nanorods on a glass substrate with an average diameter ~150 ± 10 nm. Photoluminescence measurement showed near band emission 393 nm, in agreement with the bandgap value ~3.22 eV, measured by UV-Vis spectroscopy. The developed ZnO:Ga nanorod scintillator is coupled with a commercially available photomultiplier tube and 1K Multichannel Analyser to fabricate an alpha radiation detector. The performance of the alpha radiation detector is evaluated using various activities alpha radiation sources. A large pulse height spectrum is recorded by the detector for different alpha sources against the background spectrum. The calculated detection efficiency and Minimum Detectable Activity (MDA) showed that the detector is highly sensitive to alpha radiation. The repeatability and reproducibility of the performance are studied by evaluating the response of a single scintillator for numerous exposures and by studying inter-batch response variations, respectively. The response is repeatable within ±1% whereas reproducibility varies from ±20% for extremely low activity alpha sources to ±5% for high activity alpha sources. The performance of ZnO:Ga nanorod scintillator grown on glass substrate demonstrates that it can be a promising material system for the detection of alpha radiation.

Influences of Ga Doping on Crystal Structure and Polarimetric Pattern of SHG in ZnO Nanofilms.

The second-harmonic generation (SHG) in gallium doped ZnO (GZO) nanofilms was studied. The Ga doping in GZO nanofilms influenced the crystal structure of the films, which affected SHG characteristics of the nanofilms. In our experiments, a strong SHG response was obtained in GZO nanofilms, which was excited by 790 nm femtosecond laser. It was observed that the Ga doping concentrations affected, not only the intensity, but also the polarimetric pattern of SHG in GZO nanofilms. For 5.0% doped GZO films, the SHG intensity increased about 70%. The intensity ratio of SHG between the incident light polarization angle of 90° and 0°changed with the Ga doping concentrations. It showed the most significant increase for 7.3% doped GZO films, with an increased ratio of c/a crystal constants. This result was attributed to the differences of the ratios of d33/d31 (the second-order nonlinear susceptibility components) induced by the crystal distortion. The results are helpful to investigate nanofilms doping levels and crystal distortion by SHG microscopy, which is a non-destructive and sensitive method.

Preparation and characterization of gallium-doped zinc oxide/polystyrene nanocomposite scintillator for alpha particles detection

In this study, zinc oxide (ZnO) and gallium-doped zinc oxide (GZO)/polystyrene nanocomposite films were successfully prepared. Highly luminescent powders were synthesized by a simple sol–gel method. XRD, EDX, FTIR analysis techniques, and Raman spectroscopy confirmed that ZnO and GZO nanopowders were successfully prepared. Photoluminescence and ionoluminescence studies of the synthesized powders showed that they have a brilliant blue emission at room temperature. Incorporation of GZO nanoparticles in a polystyrene (PS) matrix resulted in the formation of nanocomposite with stable and strong blue emission. According to the TEM images, the mean size of particles was estimated about 35 and 42 nm for ZnO and GZO nanopowders, respectively. The radiation response of samples was measured using 241Am alpha source. The counting rate in doped sample was improved significantly compared with ZnO composite. GZO composite showed acceptable counting efficiency which is comparable with the other expensive alpha counters. Investigations revealed that GZO/polystyrene nanocomposite can be a valuable scintillation material for the radiation detection applications.

Optically Transparent Antennas and Filters: A Smart City Concept to Alleviate Infrastructure and Network Capacity Challenges

This article discusses challenges in designing optically transparent antennas and filters for smart city applications. The smart city concept seeks to alleviate urban challenges that include infrastructure and network capacity. The proposed frequencies for the next generation of wireless networks (5G) would result in shorter broadcast distances and network dead zones. Additional access points and signal repeaters embedded into the existing infrastructure, by inserting transparent antennas into windows via either meshed conductors or transparent conductive oxides (TCOs), would help to mitigate these issues. Glass-embedded frequency-selective surfaces (FSSs) can be used anywhere that requires microwave filtering and optical transparency. The cyberphysical system security in this forthcoming network also poses challenges to entities that require strict network security. This article focuses mainly on TCOs, particularly doped zinc oxide (ZnO), as promising material for transparent antennas and filters. To demonstrate the potential of ZnOs as highly transparent conductive materials for antenna and filter applications, we designed, fabricated, and tested a gallium-doped ZnO- (GZO) based optically transparent 2.4-GHz Wi-Fi antenna and two FSSs (bandpass and bandstop filters) operating in the 23-29-GHz frequency range. These results confirm the potential for ZnO-based TCOs as suitable alternatives to indium tin oxide (ITO) for microwave applications.

Molecular orbital studies of the initial process of gallium oxide chemical vapor deposition: micro-hydrolysis of triethylgallium

Gallium-doped zinc oxide films prepared by atomic layer deposition have received much attention. When triethylgallium is hydrolyzed on the surface of zinc hydroxide, a multi-layered metal oxide film containing a specific amount of gallium at a controlled position is formed. In this study, to elucidate the micro-hydrolysis mechanism of triethylgallium, reaction mechanisms involving one or two water molecules were investigated by molecular orbital calculations. The complete hydrolysis of triethylgallium occurs in three steps with the first partial hydrolysis being the rate limiting step. The activation energy of hydrolysis by two molecules of water is ∼10 kcal mol−1 lower than that with one molecule of water for all steps. The addition of further water molecules significantly decreases the activation energy because the transition state is stabilized by hydrogen bonding between the water molecules. These results suggest the hydrolysis reaction proceeds spontaneously under mild conditions by controlling the concentration of water molecules.

Silica-Coated Ga(III)-Doped ZnO: Yb3+, Tm3+ Upconversion Nanoparticles for High-Resolution in Vivo Bioimaging using Near-Infrared to Near-Infrared Upconversion Emission.

Photon avalanche has attracted much attention due to the unique nonlinear luminescence dynamics and high-efficiency upconversion luminescence properties. In this paper, we present a simple but effective method to prepare Yb/Tm/GZO@SiO2 (GZO = gallium-doped zinc oxide). Low-threshold photon-avalanche luminescence was obtained below the milliwatts (2.5 mW) in Yb/Tm/GZO@SiO2 core/shell nanoparticles. Compared with Yb/Tm/GZO nanoparitlces, near-infrared (NIR) upconversion luminescence intensity of Yb/Tm/GZO@SiO2 was enhanced ∼12 times. Furthermore, Yb/Tm/GZO@SiO2 acted as luminescence probe, which realized the red fluorescence imaging of myocardial tissue. With injection of 6 mg/kg Yb/Tm/GZO@SiO2, the red NIR fluorescence imaging of heart tissue became brighter. The experimental results of histological assessments of representative organs indicated that there was low toxicity of Yb/Tm/GZO@SiO2 in vivo. This study proved that Yb/Tm/GZO@SiO2 posed a promising potential for bioimaging applications.

Determination of the structural, morphological and optical properties of graphene doped SnO thin films deposited by using thermionic vacuum arc technique

Tin Oxide (SnO) compounds, both SnO and SnO2 are wide band gap semiconductors, which are highly optically transparent in the visible range (400–700 nm). Graphene is also highly optically transparent and durable material. Doped SnO thin films can be defined as transparent conductive oxide (TCO) thin films, similarly to indium tin oxide (ITO), aluminum doped zinc oxide (AZO) and gallium doped zinc oxide (GZO) thin films. In this study, the graphene doped thin films are deposited onto glass and Silicon (Si) wafer substrates by using thermionic vacuum arc (TVA) technique. The structural, morphological and optical properties of graphene doped SnO thin films were investigated by various methods such as X-ray diffraction spectroscopy, atomic force microscopy, field emission scanning electron microscopy, Fourier Transform infrared spectroscopy, Raman spectroscopy, Interferometer, Fluorescence spectrometer and UV–Vis spectrophotometer. According to results, the deposited thin films have high transparency (90%), polycrystalline structure, low roughness and high homogeneity. The thicknesses of the thin films were measured as 10 nm and 8 nm deposited onto glass and Si substrate, respectively. Graphene flakes combining with other graphene flakes and SnO compounds formed diamond poly type structures along with graphene oxide (GO) structures. The band gap values of the thin films were measured as 3.11 eV and 3.33 eV deposited onto glass and Si substrate, respectively. These results show that by doping graphene the band gap value shifted towards to violet region from ultraviolet region.

Transparent conducting coatings using colloidal sols made of aluminium and gallium doped zinc oxide nanoparticles

Thin films of Transparent Conducting Oxide (TCO) using Aluminum and Galium doped Zinc Oxide (AZO and GZO) nanoparticulate suspension were doposited via simple wet chemichal deposition technique on borosilicate glass substrate. The electrical properties of the obtained films are competitive with similar layers made of tin doped indium oxide (ITO) suspension. GZO nanoparticles have smaller grain size and higher BET surface area than the AZO one. The GZO layers show better electrical conductivity than the AZO one, where a denser layer was obtained with higher charge carrier concentration and mobility. The obtained results are competitive to the reported result of tin doped indium oxide based on the similar method. Although the number of charge carriers of the metal doped zinc oxide layers are still not in a level to be replaced by ITO coatings, however it has larger charge carrier mobility, which is an emerging step to be developed to enhance the electrical conductivity of such cost effective materials. Both GZO and AZO layers exhibit a high transparency in the visible region for greater than 87%.

Resistive switching and synaptic properties modifications in gallium-doped zinc oxide memristive devices

The massively parallel computing capabilities of the human brain can be mimicked with the help of neuromorphic computing approach and this can be achieved by developing the electronic synaptic device. In the present work, we have synthesized gallium-doped ZnO thin films using a cost-effective hydrothermal method and characterized the thin films using field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. Furthermore, gallium-doped ZnO memristive devices were developed using standard procedure and electrically characterized for the neuromorphic application. In particular, resistive switching and synaptic properties of gallium-doped ZnO thin films were investigated. The bipolar resistive switching with an analog memory like behavior was observed in the developed memristive devices. In the present case, good synaptic properties, endurance, and retention characteristics were observed for 0.5% Ga doped memristive device. Our results suggested that the synaptic weight, potentiation-depression, and symmetric Hebbian learning can be tuned with properly engineering the ZnO memristive device with appropriate gallium doping. The detailed analysis of I-V results suggested that resistive switching is occurred due to Ohmic and Schottky conduction mechanisms.

Concave-shaped transparent electrode to simultaneously monitor electrical activity from multiple sites within the optical sampling area of the intact rat cerebral cortex.

We have developed a concave-shaped transparent electrode unit that enables the placement of several electrodes within the optical sampling area on the spherical surface of the rat brain. This concave-shaped transparent electrode unit consists of an insulator base (a plano-concave lens) and a gallium-doped zinc oxide film that is a transparent conductor coating the base. Most of the unit is wrapped in an insulator film made of silicon dioxide, and the few areas left unwrapped act as electrodes. In the study reported here this newly developed transparent electrode unit worked well within the optical detection area without affecting optical recording. We applied this unit to our multiple-site optical recording system for membrane potential in order to eliminate pulsation artifacts and succeeded in optically recording spontaneous neural activity, including small changes in membrane potential, in the cerebral cortex in a single-sweep recording.

Solar absorption properties of embellished GZO/Cu Janus nanoparticles

Abstract Nanofluids utilized to solar thermal utilization have been paid more attention to. In this paper, the absorption properties of the embellished gallium-doped zinc oxide (GZO)/ Copper (Cu) Janus nanoparticles have been discussed. Cu materials have localized surface plasmon resonance (LSPR) effect in visible region, and GZO materials have great absorption in near-infrared region. Therefore, GZO/Cu composite nanoparticles can achieve wide spectrum absorption. This article shows that extinction properties of embellished GZO/Cu Janus nanoparticles are improved under embellishing Cu nanoparticles on GZO surface. The radius of shell particles or core particles can tunable the extinction peaks. The photo-thermal conversion efficiency of embellished GZO/Cu Janus nanofluid increases with volume fractions, and is higher than that of GZO nanofluid. Perfect GZO/Cu Janus nanofluids have certain advantages over embellished Janus nanofluids on photo-thermal conversion efficiency, but the preparation of embellished Janus nanoparticles is simpler than that of perfect Janus nanoparticles. This work is helpful for the study of the absorption properties of embellished Janus nanoparticles under practical preparation.

Natively textured surface of Ga-doped ZnO films electron transporting layer for perovskite solar cells: further performance analysis from device simulation

In this work, the natively textured surface of gallium-doped zinc oxide (GZO) films were obtained onto quartz substrates by radio frequency magnetron sputtering. The optimal optoelectronic properties of GZO thin film exhibited the lowest resistivity 6.8 × 10−4 Ω cm, where the carrier concentration and carrier mobility were 5.3 × 1020 cm−3 and 17.3 cm2 V−1 s−1, respectively, and the transmittance above 87% in the range of 0.4–1.2 µm. Meanwhile, this GZO thin film had a low surface work function of 3.9 eV. We used a two-steps spin-coating method to deposit the perovskite films. The optical band gap of this perovskite films is 1.561 eV. The planar perovskite solar cells device modeling based on GZO electron transporting layer was performed by the Solar Cell Capacitance Simulator program. We inputted the electrical and optical parameters of GZO thin film in our perovskite solar cells simulation model. With the increasing of carrier concentration, a high-power conversion efficiency of 20.167% was obtained. Modifying GZO surface, obtaining a suitable surface work function (3.9 eV), it could reduce the interlayer contact barrier and optimize the energy level matching. At the perovskite/electron transporting layer interface, no electron barrier was formed, which facilitated electron extraction and reduced interface recombination. The higher power conversion efficiency of 21.132% was obtained.

Development of Gallium-Doped Zinc Oxide Transparent Conductive Film and Vertical Roll-to-Roll Film-Forming Equipment

Development of Gallium-Doped Zinc Oxide Transparent Conductive Film and Vertical Roll-to-Roll Film-Forming Equipment