Al Doping Concentration Research Articles

Thermal and rheological behavior of aluminium-doped zinc oxide nanofluids: Experimental study and application of artificial neural network model

In this study, the influence of Al-doping concentration on the thermal and rheological characteristics of pristine zinc oxide (ZnO) nanofluids was investigated across a range of temperatures and nanoparticle concentrations. A multilayer perceptron (MLP) artificial neural network (ANN) with an optimized topology was employed to model the thermal conductivity and viscosity of nanofluids. The addition of 0.13 M of Al-doped zinc oxide nanoparticles at 1 % rate led to a remarkable 64 % increase in the thermal conductivity of the base fluid (50:50 ratio water + ethylene glycol mixture). Furthermore, incorporating 1 % of these Al-doped nanoparticles outperformed pure zinc oxide, resulting in a 44 % boost in thermal conductivity. The enhanced heat transfer capabilities of Al-doped zinc oxide were evident across different doping and nanoparticle concentrations. The viscosity of nanofluids increases with an increase in nanoparticle concentration and decreases with an increase in temperature. ZnO and Al-doped ZnO nanoparticles have been prepared and studied their structural, morphological and elemental properties using XRD, SEM and EDS respectively. The predicted thermal and rheological behaviours are in close agreement with the experimental values.

Al concentration-dependent electrical modulation of Al-doped ZnO thin film using atomic layer deposition

A series of 150-nm-thick Al-doped ZnO (AZO) thin films with various Al doping concentrations were deposited by atomic layer deposition technique to determine their applicability in transparent electronic devices. For incorporation into transparent electrodes, the electrical properties of AZO films must be modulated to minimize the parasitic effect. The results show that AZO thin films with various Al dopant concentrations had different work-functions and electrical contact properties, while the other physical characteristics were not significantly changed. Hence, AZO thin films can be used as transparent conducting oxide materials and are potential alternatives for the currently used indium-tin-oxide (ITO) thin films.

Influence of Al doping on crystal structure, magnetic and optical properties of TiO2 compound

Recently, an attempt to search for the novel material which can be applicable for spintronics devices, has become a highly debated and intensively investigated field of study. Within the scope of this investigation, Ti1−xAlxO2 (0≤x≤0.12) polycrystalline samples were produced using the traditional solid-state reaction method, and their crystal structure, magnetic, and optical characteristics were investigated. Single rutile phase with tetragonal crystal structure of titanium oxide is seen from the X-ray diffraction patterns study. The variation in the lattice parameter elucidate that Al3+ ions successfully substitute the Ti4+ ions. The analyses of the optical characteristics reveals that the incorporation of Al into the TiO2 matrix leads to a reduction in the optical band gap. Investigation on magnetic characteristics showed that all Ti1−xAlxO2 compounds displayed room temperature ferromagnetic nature with 81Oe≤Hc≤930Oe. Hall effect measurements show that all doped samples display p-type conductivity while un-doped TiO2 exhibits n-type conductivity and with increasing Al-doping concentration, the hole carrier density rises.

Exploring threshold of Al-impurities towards high-performance Al-doped Regenerated LiCoO2

Direct regeneration, as the main recycling manner, displays the short-process and high economic value, which has been devoted to considerable attentions. Limited by the existed pre-treatments, there are still some Al-impurities of spent material, resulting in the unstable electrochemical properties of regenerated material, meanwhile the excessive removal of Al-impurities brings the risk of regeneration cost. Thus, exploring the threshold reference of Al-impurities is urgent for regeneration of spent materials. Herein, through the introduction of Al2O3 with different content, spent LiCoO2 were successfully regenerated, displaying the evolution of physical-chemical properties. With suitable Al adding (0.02 wt.%), the broadening layer distance and storage space are found. As a cathode, the as-optimized sample shows a capacity of 172.7 mAh g−1 at 0.2 C, and the capacity retention was 84 % after 500 cycles at 5.0 C, even better than Al-impurity-free regenerated sample. Supported by the detailed kinetic analysis, it could be deduced that, suitable Al-introduction is beneficial for the fast insertion/extraction of ions, meanwhile too excess adding could bring about the blocking of diffusion paths and by-production surface stacking. Given this, this work is expected to shed light on the physical-chemical effect of Al-impurities, meanwhile offering the threshold reference for Al-doping content in practical regenerated industry.

Impact of Al Alloying/Doping on the Performance Optimization of HfO2-Based RRAM

Al alloying/doping in HfO2-based resistive random-access memory (RRAM) has been proven to be an effective method for improving the low-resistance state (LRS) retention. However, a detailed understanding of Al concentration on oxygen vacancy migration and resistive switching (RS) behaviors still needs to be included. Herein, the impact of Al concentration on the RS properties of the TiN/Ti/HfAlO/TiN RRAM devices is addressed. Firstly, it is found that the forming voltage, SET voltage, and RESET voltage can be regulated by varying the Al doping concentration. Moreover, we have demonstrated that the device with 15% Al shows the minimum cycle-to-cycle variability (CCV) and superior endurance (over 106). According to density-functional theory (DFT) calculations, it is found that the increased operation voltage, improved uniformity, and improved endurance are attributed to the elevated migration barrier of oxygen vacancy through Al doping. In addition, LRS retention characteristics of the TiN/Ti/HfAlO/TiN devices with different Al concentrations are compared. It is observed that the LRS retention is greatly enhanced due to the suppressed lateral diffusion process of oxygen vacancy through Al doping. This study demonstrates that Al alloying/doping greatly affects the RS behaviors of HfO2-based RRAM and provides a feasible way to improve the RS properties through changing the Al concentration.

Effect of Al and Si content on properties of Ti(1-x-y)AlxSiyN coating materials: First-principles calculation

This paper investigates the effect of Al and Si atomic doping on the Ti(1-x-y)AlxSiyN alloy using density functional theory (DFT). The results indicate that the phase structure stability of the alloy decreases with increasing Al and Si doping content. Particularly, excessive doping leads to the transformation of crystal structure from rocksalt to wurtzite structure with lower mechanical properties. The bulk modulus of the alloy decreases with the increase of doping content. Specifically, Al atom doping initially reduces and then increases the shear modulus and Young's modulus of Ti1-xAlxN, while Si atom doping causes the shear modulus and Young's modulus of Ti0.375-yAl0.625SiyN to increase first and then decrease. In terms of hardness, the hardness of Ti1-xAlxN increases with the increase of Al doping, but the toughness decreases. Si atom doping further enhances the alloy's hardness, reaching a maximum of 29.8 GPa, consistent with the trends observed in experimental results. Electronic structure analysis reveals that Al and Si doping induces orbital hybridization, enhancing the bonding ability and chemical bond strength between atoms. The results confirm that the ionic bonds, metal bonds and covalent bonds in multi-component nitride jointly determine the mechanical properties of the alloy.

Synthesis and characterization of Al-doped ZnO thin-films for photovoltaic applications

The investigation reports on the effect of aluminum-doped zin oxide (Al:ZnO), using sol–gel dip coating method for deposing thin films at different Al doping concentration values ​​(i.e., 0, 2, 3, 4, 5, and 10 atomic %).The as-grown films have been examined through structural and optical investigations. The X-ray pattern reveals the highly desired hexagonal wurtzite crystal structure that is orientated in a direction of (002). When the Al doping concentration rises from 0 % to 10 %, the average size of the crystallites decreases (from 22 nm to 19 nm). The optical properties measured using UV–visible spectroscopy indicated significant enhancement with Al doping concentration due to light scattering. Dopants have a slight effect on the band gap energy; fluctuations are seen between 3.21 and 3.25 eV. Measurements of ZnO and ZnO:Al thin films’ extinction coefficient and refractive index revealed that the doping concentration of Al had a small effect on both. When the Al content reaches 10 % at. %, the optical properties gradually approach their highest value, encouraging further exploration of its viability in solar cell applications.

Microstructure and optical properties of ZnAlO films prepared by Magnetron sputtering

ZnAlO thin films with different Al concentrations were prepared on glass and silicon substrates by Magnetron sputtering in this paper. Scanning electron microscopy (SEM), X-ray diffraction (XRD), spectrometer and other instruments were used to analyze the surface morphology, microstructure, transmittance and Raman spectrum of the films. The results showed that trace Al doping significantly increased the surface morphology and size of ZnAlO thin films; The low doped ZnAlO thin film exhibits a good preferred orientation. As the Al doping concentration increases, the main growth direction of the crystal gradually shifts from (101) to (103), and the grain size decreases with the increase of doping concentration during low doping; When the wavelength of ZnAlO film is less than 330 nm, the transmittance of the film is almost zero; When the wavelength is greater than 350 nm, the transmittance of the thin film decreases with the increase of Al doping concentration, and there is a blue shift trend with the increase of Al concentration. When the wavelength is between 420-900nm, the average transmittance of ZnAlO thin film can reach over 90%, and the transmission performance is good; The ZnAlO thin films all have structural characteristic peaks of wurtzite with a frequency of about 437 cm−1, and the Raman peak position does not move with the increase of Al concentration.

Towards wake-up free ferroelectrics and scaling: Al-doped HZO and its crystallographic texture

Ferroelectric (FE) hafnium zirconium oxide (HZO) is an excellent candidate for data storage applications. However, it has some reliability limitations such as imprint and retention. Herein, we explore Al doping of HZO to overcome these limitations. FE behavior is tuned by the aluminum (Al) concentrations in the films and by annealing temperature. A correlation is done between electrical behavior, crystallographic texture, and FE phases determined by grazing-incidence X-ray diffraction (GIXRD) measurements. Reduced coercive field (2Ec) values and wake-up free HZO-based ferroelectrics are explored. We show the tunability of remanent polarization (2Pr) and 2Ec with respect to Al-doping concentration and anneal temperature, hence crystallographic texture.

Photoelectrical characterization of heavily doped p-SiC Schottky contacts

The availability of photoelectrical characterizations of heavily Al-doped p-SiC Schottky contacts was clarified. We conducted a systematic study of four samples with different Al doping concentrations from 1 × 1018 to 5 × 1019 cm−3. Although the current–voltage (I–V) characteristics had lost rectification, reasonable Schottky barrier height (qϕ B) values were obtained up to 1 × 1019 cm−3 by capacitance voltage, photo response, and scanning internal photoemission microscopy (SIPM) measurements. In the two-dimensional characterization by SIPM, large photocurrent spots corresponding with low qϕ B were observed in an average density of 103 to 104 cm−2. However, except for these spots, a high uniformity of about 2 meV standard deviation was obtained for qϕ B over the entire observed electrodes. These results indicate that SIPM is able to characterize the inhomogeneity of heavily doped p-SiC contacts with very leaky I–V characteristics.

Dependence of Positive Bias Stress Instability on Threshold Voltage and Its Origin in Solution-Processed Aluminum-Doped Indium Oxide Thin-Film Transistors.

The initial electrical characteristics and bias stabilities of thin-film transistors (TFTs) are vital factors regarding the practical use of electronic devices. In this study, the dependence of positive bias stress (PBS) instability on an initial threshold voltage (VTH) and its origin were analyzed by understanding the roles of slow and fast traps in solution-processed oxide TFTs. To control the initial VTH of oxide TFTs, the indium oxide (InOx) semiconductor was doped with aluminum (Al), which functioned as a carrier suppressor. The concentration of oxygen vacancies decreased as the Al doping concentration increased, causing a positive VTH shift in the InOx TFTs. The VTH shift (∆VTH) caused by PBS increased exponentially when VTH was increased, and a distinct tendency was observed as the gate bias stress increased due to a high vertical electric field in the oxide dielectric. In addition, the recovery behavior was analyzed to reveal the influence of fast and slow traps on ∆VTH by PBS. Results revealed that the effect of the slow trap increased as the VTH moved in the positive direction; this occured because the main electron trap location moved away from the interface as the Fermi level approached the conduction band minimum. Understanding the correlation between VTH and PBS instability can contribute to optimizing the fabrication of oxide TFT-based circuits for electronic applications.

Migration properties of Li<sup>+ </sup>in Li<sub>1+<i>x</i> </sub>Al<sub><i>x</i></sub>Ti<sub>2–<i>x</i></sub>(PO<sub>4</sub>)<sub>3</sub>

NASICON-type materials are specific skeleton structures in which ions move in three dimensions. Li<sub>1+<i>x</i></sub>Al<sub><i>x</i></sub>Ti<sub>2–<i>x</i></sub>(PO<sub>4</sub>)<sub>3</sub> (LATP) is a promising NASICON-type solid-state electrolyte for Li-ion batteries, due to its relatively high Li<sup>+</sup> conductivity, chemical stability to air and moisture, and mechanical strength. Motivated by this, we study the doping and electronic properties of Li<sub>1+<i>x</i></sub>Al<sub><i>x</i></sub>Ti<sub>2–<i>x</i></sub>(PO<sub>4</sub>)<sub>3</sub> (<i>x</i> = 0.00, 0.16, 0.33, 0.50) and the transport properties of Li<sup>+</sup> in them by using first-principles calculations based on density functional theory as implemented in Vienna <i>ab initio</i> Simulation Package (VASP). The results indicate that Al can substitute Ti to form a stable structure. When the Al doping concentration is <i>x</i> = 0.16, the average bond length of Li—O bond is longest and the bonding strength is weakest, this may lead to the expansion of channels for Li<sup>+</sup> migration, which facilitates the diffusion of Li<sup>+</sup>. With the increase of Al doping concentration, the strength of Ti—O bond remains almost unchanged. The electronic structure calculations exhibit that with the increase of Al doping concentration, the bandgap of LATP does not change much, and LATP shows semiconductor characteristic. The differential charge results indicate that more electrons are localized on O-atoms surrounding the Al-dopant, causing the AlO<sub>6</sub> groups to form polarization centers. The study on the migration properties of Li<sup>+</sup> indicates that Li<sup>+</sup> exhibits different migration characteristics in three different migration modes (vacancy migration, interstitial migration, and cooperative migration). With the increase of Al doping concentration, the migration barrier of Li<sup>+</sup> increases via vacancies involving only lattice site migration, and the migration barrier for LATP-0.16 is lowest (0.369 eV). While in interstitial migration involving only interstitial sites, the migration barrier of Li<sup>+</sup> decreases accordingly. When the Al doping concentration is <i>x</i> = 0.50, the migration barrier is lowest (0.342 eV). In terms of cooperative migration, this migration mode involves both vacancy and interstitial sites, so the migration barrier first decreases and then increases with the increase of Al doping concentration. Thus, our study suggests that by varying the concentration of Al doping, the interstitial Li<sup>+</sup> content, migration channel structure, and the migration performance of Li<sup>+</sup> can be changed favorably. Our results provide a theoretical basis for improving the ion conductivity of Li in LATP by varying the Al doping concentration in experiment.

Effects of Al doping concentration and top electrode on the ferroelectricity of Al-doped HfO2 thin films

Al-doped HfO2 (HAO) is regarded as one of the potential HfO2 ferroelectric materials owing to its compatibility with the front end of the line process in integration circuits. In this work, atomic layer deposited (ALD) HAO thin films with different Al-doping concentrations and the corresponding devices with Ti or W top electrodes have been explored. It is found that the HAO film properties and corresponding ferroelectric device performances depend greatly on the doping concentration. In the concentration range of 3.0%–5.0%, 4.5% is the most proper doping concentration to induce the ferroelectricity of the thin film. It is revealed by x-ray diffraction and photoelectron spectroscopy that the oxygen vacancies can be modulated by doping, thereby contributing to the formation of the ferroelectric orthorhombic phase. A high remnant polarization (2Pr) of 36.8 ± 0.7 μC/cm2 under 5 mV/cm sweeping is observed through electrical measurement in the device with a 4.5% HAO and W top electrode. In addition, it was found that the choice of W or Ti top electrodes would affect the leakage and breakdown characteristics of the device. This work reveals the mechanism of Al doping and electrode modulation of HfO2 device performance and promotes the development of HAO ferroelectric thin film devices.

SYNTHESIS AND CHARACTERIZATION OF Al-DOPED ZnO THIN FILMS AS ANTI-REFLECTION COATINGS FOR SOLAR CELL APPLICATIONS

In this work, we have synthesized ZnO:Al thin films by pulsed laser deposition technique and investigated their microstructural and optical properties. The XRD study confirmed a polycrystalline structure of wurtzite ZnO in all films. Further, Al doping has improved the crystallinity and decreased the crystal size and volume of the unit cell. The surface morphology was homogeneous with nanoscopic crystals clustered to form granular nanoparticles. The optical properties significantly improved by increasing the Al doping concentration. The produced thin films are excellent candidates for use as an anti-reflection layer in solar cells due to their outstanding properties.

Neuromorphic synaptic applications of HfAlOx-based ferroelectric tunnel junction annealed at high temperatures to achieve high polarization

HfO2-based ferroelectric tunnel junctions (FTJs) are promising nonvolatile memory types for neural network applications because of their speed, low power, and excellent complementary metal-oxide semiconductor compatibility. Specifically, HfAlOx (HAO) has led to extensive research efforts owing to its outstanding ferroelectric performance. This is a result of the fact that the atomic radius of Al is smaller than that of Hf. In this study, we investigate the metal–ferroelectric–semiconductor device with an Al doping concentration of 2% that was annealed at 900 °C. A high-remnant polarization (Pr) value of 39.85 µC/cm2 and endurance were achieved by using the polarization switching positive-up-negative-down measurement method at this annealing condition. Our device shows long-term potentiation and depression properties, including high linearity and multiple conductance states for neuromorphic applications. Moreover, paired-pulse facilitation was implemented to mimic human synaptic functions. The construction of 16 states comprising four bits was achieved by employing reservoir computing with the FTJ device functioning as a physical reservoir. Finally, the results obtained from the experiment show promising outcomes for the ferroelectric memory characteristics and synaptic properties of the manufactured HAO device.

Improved photoelectrochemical sensitivity of Al-doped ZnO nanostructure prepared by co-precipitation and spin-coating techniques

In this paper we report on co-precipitation and spin-coating process to synthesize pure and aluminum (Al) doped nanostructured zinc oxide thin layers. X-ray diffraction (XRD) technique was involved to investigate the crystalline properties of prepared layers. XRD analysis indicated that the films were indexed as the hexagonal phase of wurtzite-type structure. Al doping revealed a significant effect on the optical measurements, where the band gap has been shifted from 3.22 eV for pure ZnO film to 3.27 eV after Al doping. Additionally, among all photo-anodes with different Al dopant concentrations, the sample with 1 at.% Al:ZnO film exhibited the fastest response and highest photoconduction sensitivity.

Microstructure evolution and mechanical properties of Al doped ta-C films prepared by filtered cathodic vacuum arc

Al-doped tetrahedral amorphous carbon (ta-C) films were prepared by filtered cathodic vacuum arc technique. Effect of Al content on the structure and properties of the ta-C film were systematically investigated. Results showed that Al content in films increased from 0 to 39.5 at. % as the Al target current altered from 0 to 2 A. Without Al doping, ta-C film mainly presented amorphous characteristic with disordered arrangement and compact structure. With a small amount of Al doping, the film maintained the amorphous phase structure, and Al atoms mainly existed in the carbon tetrahedral interstitial space in the form of solid solution. At high Al doping content, the formed Al nanoparticles embedded in the carbon matrix network. Meanwhile, the addition of Al could promote the graphitization of films. The residual stress of ta-C films decreased gradually with increase of Al content. Furthermore, the hardness and elastic modulus of films also decreased with increasing Al content. That's ascribed to the reduction of residual stress and graphitization of the carbon structure. In addition, the ta-C film with Al addition could effectively improve the friction and wear properties of films at both room and high temperature. The friction coefficient decreased with the increase of Al content at room temperature (RT). At 400 °C, the film containing 7.6 at. % Al obtained the lowest friction coefficient and wear rate, corresponding to the values of 0.29 and 12.3 × 10−8 mm3/N⋅m, respectively.

Magneto-optical absorption in an asymmetric finite quantum well

We examine the influence of internal (confinement frequency, Al-doped concentration, β parameter) and extrinsic (magnetic field, temperature) parameters on the energy differences and magneto-optical absorption properties of a finite semi-parabolic plus semi-inverse squared (FSPSISP) quantum well. Our results demonstrated that the energy difference between the ground and excited states is substantially dependent on the amount of Al-doped in the system, the confinement frequency, and the magnetic field, and slightly dependent on parameter characterizing the inverse squared part of the confinement potential, but not temperature. The magneto-optical absorption coefficient (MOAC) increases with confinement frequency, Al-doped concentration, magnetic field, and temperature, but decreases with β. The full width at half maximum (FWHM) increases with all parameters. By optimizing these parameters, we can enhance the MOAC. Our results provide deeper insight into the optical properties of low-dimensional systems with finite confinement potential.

Enabling high-quality transparent conductive oxide on 3D printed ZrO2 architectures through atomic layer deposition

The conformal atomic layer deposition of a transparent conductive oxide composed of Al-doped ZnO (AZO) over three-dimensional (3D) shaped ZrO2 microarchitectures produced using two-photon lithography (TPL) is reported here for the first time. The effect of ZrO2 morphology, surface roughness, and crystallographic phase (tetragonal and monoclinic) on the quality and properties of the deposited ZnO and AZO thin films is investigated. No discontinuities, domains, or areas differing from the desired chemical composition have been found in films grown over the 3D structures. Three different Al dopant concentrations (4.0 %, 4–5 %, and 5.0 % Al doping cycles) are examined and compared to undoped ZnO. AZO and ZnO optical and electrical properties are studied using cathodoluminescence (CL) and Hall effect measurements. The CL study confirms that the observed emissions from the ZnO and AZO films are associated with the near band emission of ZnO and defects, i.e., zinc and oxygen vacancies and interstitial oxygen. The AZO films exhibit n-type semiconductor behavior, and a minimum resistivity of 1.2 × 10-3 Ω cm is achieved. From a broad perspective, AZO deposition on 3D microarchitectures opens a new route towards dimensionally refined optoelectronic devices in which the ZrO2/AZO can serve as an enabling role for the production of electrodes.

Effect of Al Concentration on Structural, Optical and Electrical Properties of (Gd, Al) Co-Doped ZnO and Its n-ZnO/p-Si (1 0 0) Heterojunction Structures Prepared via Co-Sputtering Method

Heterojunction structures of n-ZnO/p-Si were prepared through the growth of undoped ZnO and (Gd, Al) co-doped ZnO films onto p-type Si (1 0 0) substrates, using a co-sputtering method. The structural and optical properties of the Gd-doped ZnO films were studied as a function of different Al doping concentrations. The X-ray diffraction profiles indicated that the films had a nanocrystalline structure of ZnO with a (0 0 2) preferential orientation. An increase in the Al doping concentration deteriorated the (0 0 2) diffraction peak intensity. The transmittance measurements in the UV-Vis wavelength range indicated that the film's optical gap increased with increase in Al doping concentration. The heterojunction parameters were evaluated using the current-voltage (I-V) characterization carried out of the fabricated n-ZnO/p-Si heterostructure, in dark conditions at room temperature. From these measurements, the n-ZnO-based DMS/p-Si heterojunction diode with the use of (Gd, Al) co-doped ZnO film showed the lowest leakage current of 1.28 × 10-8 A and an ideality factor η of 1.11, close to the ideal diode behavior of η = 1, compared to the n-Gd-doped ZnO/p-Si and n-undoped ZnO/p-Si heterojunction diodes.