Search Results (50)

Al-doped zinc oxide (AZO) thin films were deposited by RF magnetron sputtering using a simple doping approach: aluminum tape was placed directly on the ZnO target. The work focused on understanding how Al incorporation, annealing temperature, and annealing atmosphere affect the structural and electrical behavior of the films, particularly their baseline resistance for gas sensing applications. EDX measurements confirmed that increasing the Al-covered area on the target progressively increased the Al concentration in the deposited layers. XRD analysis showed that higher Al contents and stronger thermal treatments reduced crystallinity and promoted the formation of smaller crystallites. The electrical response changed markedly with both Al incorporation and thermal treatment. Pure ZnO films initially exhibited very high resistance, while annealing reduced it by several orders of magnitude. Further increasing the Al concentration improved conductivity due to the donor effect of Al in the ZnO lattice. Overall, the results show that RF sputtering and post-treatment strategies can provide broad control over the electrical resistance of ZnO-based thin films. This tunability makes AZO coatings attractive for adapting chemoresistive gas sensors to different sensing environments and operating regimes, and deposition and thermal treatment parameters determine the resistance range. Full article

ZnO nanorods were synthesized on AZO substrates by chemical bath deposition, and were subsequently annealed under an air and vacuum ambient. Both annealing processes could improve the crystallinities of ZnO nanorods. The air-annealed ZnO nanorods showed higher crystallinity and partial reduction of oxygen-vacancy-related defects. The air-annealed ZnO nanorods exhibited a much higher photodegradation efficiency of 70% degradation for methyl red. In addition, as-grown ZnO nanorods were coated with undoped and Al-doped ZnO by mist chemical vapor deposition. Both coated thin layers modified the surface of ZnO nanorods, while the AZO-coated ZnO nanorods showed higher crystallinity and light absorption which resulted in the improvement in the photodegradation rate of methyl red. These findings demonstrate that appropriate annealing treatment and AZO surface engineering for ZnO nanorods are effective approaches for improving crystallinity, which leads to improvement of the photocatalytic efficiency of ZnO-based materials. Full article

This study investigates pristine and doped ZnO thin films fabricated via the sol-gel technique, aiming to address efficiency challenges when used as transparent conductive oxide (TCO) layers in thin-film solar cells. ZnO was first doped with aluminum (Al), and subsequently with both Al and reduced graphene oxide (rGO), to evaluate the individual and combined effects of these dopants. The optimal pH value for the ZnO structure was initially determined, with the film produced at pH 9 exhibiting the most favorable characteristics. Al doping was then optimized at a ratio of Al/(Al + Zn) = 0.2, followed by optimization of the graphene content at 1.5 wt%. In this context, the structural, optical, and electrical properties of pristine ZnO, Al-doped ZnO (AZO), and Al and graphene co-doped ZnO (Gr:AZO) thin films were systematically investigated. These films were integrated as TCO layers into Cu₂SnS₃ (CTS)-based thin-film solar cells fabricated via physical vapor deposition (PVD). The cell architecture employed an 80 nm pristine ZnO window layer, while the doped ZnO films (300 nm) served as TCO layers. To assess the influence of the chemically deposited top layers, device performance was compared against a reference cell in which all layers were fabricated entirely using PVD. As expected, the reference cell exhibited superior performance compared to the cell whose AZO layer deposited chemically; however, the incorporation of both Al and graphene significantly enhanced the efficiency of the chemically modified cell, outperforming devices using only pristine or singly doped ZnO films. These results demonstrate the promising potential of co-doped solution-processed ZnO films as an alternative TCO layer in improving the performance of thin-film solar cell technologies. Full article

We report the fabrication and characterization of Al-doped ZnO (AZO) optoelectronic synaptic devices based on sol–gel-derived thin films with varying Al concentrations (0~4.0 wt%). Structural and optical analyses reveal that moderate Al doping modulates the crystal orientation, optical bandgap, and defect levels of ZnO films. Notably, 2.0 wt% Al doping yields the widest bandgap (3.31 eV), stable PL emission, and uniform deep-level absorption without inducing significant lattice disorder. Synaptic performance, including learning–forgetting dynamics and persistent photoconductivity (PPC), is strongly dependent on Al concentration. The 2.0 wt% AZO device exhibits the lowest forgetting rate and longest memory retention due to optimized trap formation, particularly Al–oxygen vacancy complexes that enhance carrier lifetime. Visual memory simulations using a 3 × 3 pixel array under patterned UV illumination further confirm superior long-term memory (LTM) behavior at 2.0 wt%, with stronger excitatory postsynaptic current (EPSC) retention during repeated stimulation. These results demonstrate that precise doping control via the sol–gel method enables defect engineering in oxide-based neuromorphic devices. Our findings provide an effective strategy for designing low-cost, scalable optoelectronic synapses with tunable memory characteristics suitable for future in-sensor computing and neuromorphic vision systems. Full article

The rising demand for sustainable energy solutions has spurred the development of advanced materials for photovoltaic devices. Among these, transparent conductive oxides (TCOs) play a pivotal role in enhancing device efficiency, particularly in silicon-based solar cells. However, the reliance on indium-based TCOs like ITO raises concerns over cost and material scarcity, prompting the search for more abundant and scalable alternatives. This study focuses on the fabrication and characterization of aluminum-doped zinc oxide (ZnO:Al, AZO) thin films deposited via Atomic Layer Deposition (ALD), targeting their application as transparent conductive oxides in silicon solar cells. The ZnO:Al thin films were synthesized by alternating supercycles of ZnO and Al₂O₃ depositions at 225 °C, allowing precise control of composition and thickness. Structural, optical, and electrical properties were assessed using Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), Transmission Electron Microscopy (TEM), Raman spectroscopy, spectroscopic ellipsometry, and four-point probe measurements. The results confirmed the formation of uniform, crack-free ZnO:Al thin films with a spinel-type ZnAl₂O₄ crystalline structure. Optical analyses revealed high transparency (more than 80%) and tunable refractive indices (1.64 ÷ 1.74); the energy band gap was 2.6 ÷ 3.07 eV, while electrical measurements demonstrated low sheet resistance values, reaching 85 Ω/□ for thicker films. This combination of optical and electrical properties underscores the potential of ALD-grown AZO thin films to meet the stringent demands of next-generation photovoltaics. Integration of Zn:Al thin films into silicon solar cells led to an optimized photovoltaic performance, with the best cell achieving a short-circuit current density of 36.0 mA/cm² and a power conversion efficiency of 15.3%. Overall, this work highlights the technological relevance of ZnO:Al thin films as a sustainable and cost-effective alternative to conventional TCOs, offering pathways toward more accessible and efficient solar energy solutions. Full article

The first part of this work evaluates Al-doped ZnO (AZO) as an optically transparent top-gate material for studies on semiconductor quantum dots. In comparison with conventional Ti gates, samples with AZO gates demonstrate a more than three times higher intensity in the quantum dot emission under comparable excitation conditions. On the other hand, charges inside a process-induced oxide layer at the interface to the semiconductor cause artifacts at gate voltages above $U\approx$ 1 V. The second part describes an optical and simulation study of a vertical electric-field (F)-induced switching from a strong to an asymmetric strong–weak confinement in GaAs cone-shell quantum dots (CSQDs), where the charge carrier probability densities are localized on the surface of a cone. These experiments are performed at low U and show no indications of an influence of interface charges. For a large F, the measured radiative lifetimes are substantially shorter compared with simulation results. We attribute this discrepancy to an F-induced transformation of the shape of the hole probability density. In detail, an increasing F pushes the hole into the wing part of a CSQD, where it forms a quantum ring. Accordingly, the confinement of the hole is changed from strong, which is assumed in the simulations, to weak, where the local radius is larger than the bulk exciton Bohr radius. In contrast to the hole, an increasing F pushes the electron into the CSQD tip, where it remains in a strong confinement. This means the radiative lifetime for large F is given by an asymmetric confinement with a strongly confined electron and a hole in a weak confinement. To our knowledge, this asymmetric strong–weak confinement represents a novel kind of quantum mechanical confinement and has not been observed so far. Furthermore, the observed weak confinement for the hole represents a confirmation of the theoretically predicted transformation of the hole probability density from a quantum dot into a quantum ring. For such quantum rings, application as storage for photo-excited charge carriers is predicted, which can be interesting for future quantum photonic integrated circuits. Full article

This research, which involved a comprehensive methodology, including depositing electroplated copper on a copper seed layer and Al-doped ZnO (AZO) thin films on textured silicon substrates using DC magnetron sputtering with varying substrate heating, has yielded significant findings. The study thoroughly investigated the effects of substrate temperature (Ts) on copper adhesion strength and morphology using the peel force test and electron microscopy. The peel force test was conducted at angles of 90°, 135°, and 180°. The average adhesion strength was about 0.2 N/mm for the samples without substrate heating. For the samples with substrate heating at 100 °C, the average peeling force of the electroplated copper film was about 1 N/mm. The average peeling force increased to 1.5 N/mm as the substrate heating temperature increased to 200 °C. The surface roughness increases as the annealing temperature of the Cu/AZO/Si sample increases. These findings not only provide a reliable and robust method for applying AZO transparent conductive films onto silicon solar cells but also underscore its potential to significantly enhance the efficiency and durability of solar cells significantly, thereby instilling confidence in the field of solar cell technology. Full article

Compared with purely electrical neuromorphic devices, those stimulated by optical signals have gained increasing attention due to their realistic sensory simulation. In this work, an optoelectronic neuromorphic device based on a photoelectric memristor with a Bi₂FeCrO₆/Al-doped ZnO (BFCO/AZO) heterostructure is fabricated that can respond to both electrical and optical signals and successfully simulate a variety of synaptic behaviors, such as STP, LTP, and PPF. In addition, the photomemory mechanism was identified by analyzing the energy band structures of AZO and BFCO. A convolutional neural network (CNN) architecture for pattern classification at the Mixed National Institute of Standards and Technology (MNIST) was used and improved the recognition accuracy of the MNIST and Fashion-MNIST datasets to 95.21% and 74.19%, respectively, by implementing an improved stochastic adaptive algorithm. These results provide a feasible approach for future implementation of optoelectronic synapses. Full article

This paper presents a detailed analysis of aluminium-doped zinc oxide (AZO) thin films and considers them a promising alternative to indium tin oxide in transparent electrodes. The study focusses on critical properties of AZO, including optical, electrical, and mechanical properties, with potential applications in displays, photovoltaic cells, and protective coatings. The deposited AZO thin films are characterised by excellent optical and electrical parameters, with transparency in the visible light range exceeding 80% and resistivity of 10⁻³ Ω·cm, which gives a high value of figure of merit of 63. Structural analysis confirms the nanocrystalline nature of as-deposited AZO thin films, featuring hexagonal ZnO, orthorhombic Al₂O₃, and cubic Al₂ZnO₄ phases. The study includes nanoindentation measurements, which reveal exceptional hardness (11.4 GPa) and reduced elastic modulus (98 GPa), exceeding typical values reported in the literature, highlighting their protective potential. Abrasion tests have shown extraordinary scratch resistance due to the lack of impact on topography and surface roughness up to 10,000 cycles. This comprehensive study demonstrated that as-deposited AZO thin films are multifunctional materials with exceptional optical, electrical, and mechanical properties. The findings open up possibilities for a variety of applications, especially in protective coatings, where the combination of hardness, scratch resistance, and transparency is both rare and valuable. Full article

In this study, pure ZnO and Al-doped ZnO(AZO) thin films were coated onto a SiO₂ wafer using the electrostatic spray deposition (ESD) process for acetone gas detection under laboratory conditions. Voltage levels were varied to determine the optimal conditions for producing thin films with the highest uniformity. The results indicate that the optimal coating voltage for achieving the highest uniformity of the coated films is 2.9 kV for ZnO and 2.6 kV for AZO. The thin films were produced under these optimal ESD conditions by adjusting the coating time, and gas sensors were fabricated by printing electrodes using a reverse offset process on top of the thin films. Analysis of the sensing response revealed that the AZO-coated gas sensor with a 200 s deposition exhibited the best acetone-sensing ability at 300 °C, with a maximum response of 13.41 at 10 ppm. Furthermore, the fabricated gas sensors effectively detected acetone gas even at a low concentration of 2 ppm, demonstrating high selectivity in comparison to other gases. Full article

This work analyzed and compared the optical and photoenergetic properties of low-emissivity coatings made from various dielectric materials deposited through magnetron sputtering following a systematic, comparable method. Different multilayer structures of silver-based low-emissivity coatings were studied using SnO₂, ZnO, SiAlN_x, and aluminum-doped zinc oxide (AZO, which is inherently a semiconductor, but it fulfils an optical dielectric function in this type of structure). The properties of the coatings were determined by spectrophotometric and sheet resistance measurements. Coatings with AZO as the dielectric layers obtain the best photoenergetic performance because silver growth is more efficient on AZO. We also studied the effect of ion bombardment on AZO and SiAlN_x in an attempt to obtain a better low-emissivity coating, achieving better results when etching the dielectric layer with an ion gun. Regarding the structures’ visible transmission, the oxides produced better transmission results. Based on the above, we concluded that AZO had the best optical and photoenergetic properties in our deposition system, observing, in the best-case scenario, improvements in emissivity from 0.083 with SnO₂ to 0.058 with AZO and to 0.052 using an ion beam on AZO and improvements in visible transmission from 81.9% with SnO₂ to 86.8% with AZO. Full article

One of the major limitations causing deadlock in solar cells with higher sulfur content in the photovoltaic absorber material is the unintended formation of an uncontrollable MoS₂ layer between the absorber material and Mo back contact, which can affect negatively the efficiency of solar cells. Researchers reported that it is very difficult to control the MoS₂ properties such as the conductivity type, thickness, band gap, and carrier concentration in experiments. Considering these challenges, an initial step involved a thorough examination utilizing the one-dimensional solar cell capacitance simulator (SCAPS-1D) to assess the impact of n-MoS₂ interlayer thickness and donor concentration on the performance of CMTS solar cells. Our investigation revealed the formation of a “cliff-like CBO” at the CMTS/n-MoS₂ interface, facilitating the transport of electrons from the p-CMTS absorber to the Mo back contact, resulting in a significantly higher recombination rate. Subsequently, herein a novel approach is proposed, using Cu₂O as a back surface field (BSF) layer due to its low cost, intrinsic p-type properties, and non-toxic nature. Simulation results of a novel heterostructure (Mo/Cu₂O/CMTS/CdS/i-ZnO/AZO/Al) of the CMTS-based solar cell are discussed in terms of recombination rate and conduction band alignment at the absorber/BSF interface. A desired “spike-like CBO” is formed between CMTS/Cu₂O, which hinders the transport of electrons to the back contact. By optimizing the physical parameters such as thickness and the doping density of the Cu₂O layer, an efficiency η of 21.78% is achieved, with an open circuit voltage (Voc) of 1.26 V, short-circuit current density (Jsc) of 24.45 mA/cm², and fill factor (FF) of 70.85%. Our simulation results offer a promising research direction to further develop highly efficient and low-cost CMTS solar cells. Full article

Transparent conductors (TC) have been widely applied in a wide range of optoelectronic devices. Nevertheless, different transparent spectral bands are always needed for particular applications. In this work, indium tin oxide (ITO)-free TCs with tunable transparent bands based on the film structure of TiO₂/Ag/AZO (Al-doped ZnO) were designed by the transfer matrix method and deposited by magnetron sputtering. The transparent spectra and figure-of-merit (FOM) were effectively adjusted by precisely controlling the Ag layer’s thickness. The fabricated as-deposited samples exhibited an average optical transmittance larger than 88.3% (400–700 nm), a sheet resistance lower than 7.7 Ω.sq⁻¹, a low surface roughness of about 1.4 nm, and mechanical stability upon 1000 bending cycles. Moreover, the samples were able to hold optical and electrical properties after annealing at 300 °C for 60 min, but failed at 400 °C even for 30 min. Full article

ZnO and Al-doped ZnO (AZO) thin films were prepared using the sol–gel method and deposited on a Silicon (Si(100)) substrate using the dipping technique. The structure, morphology, thickness, optical constants in the spectral range 300–1700 nm, bandgap (E_g) and photoluminescence (PL) properties of the films were analyzed using X-ray diffractometry (XRD), X-ray fluorescence (XRF), atomic force microscopy (AFM), scanning electron microscopy (SEM), spectroscopic ellipsometry (SE), Raman analysis and PL spectroscopy. The results of the structure and morphology analyses showed that the thin films are polycrystalline with a hexagonal wurtzite structure, as well as continuous and homogeneous. The PL background and broader peaks observable in the Raman spectra of the AZO film and the slight increase in the optical band gap of the AZO thin film, compared to undoped ZnO, highlight the effect of defects introduced into the ZnO lattice and an increase in the charge carrier density in the AZO film. The PL emission spectra of the AZO thin film showed a strong UV line corresponding to near-band-edge ZnO emission along with weak green and red emission bands due to deep-level defects, attributed to the oxygen-occupied zinc vacancies (O_Zn lattice defects). Full article

As transparent heated films (THFs) based on transparent conductive oxides (TCOs) are restricted by expensive raw materials and inappropriate fabricating film on curved surfaces because of its brittleness, silver nanowires transparent conductive film (AgWS-TCF) is an ideal alternative material for THF. However, there are still many problems to be solved in the electrical and thermal stability of AgNWs-TCF. In this paper, an Al-doped ZnO (AZO) nanoparticles produced by magnetron sputtering was used to modify and coat the AgNWs network, and the ceramic /AgNWs@AZO-TCF was obtained. Compared with ceramic/AgNWs-TCF, the sheet resistance of ceramic/AgNWs@AZO-TCF decreased from 53.2 to 19.3 Ω/sq, resistance non-uniformity decreased from 18.0% to 7.0%, and the inoxidizability, current-impact resistance, and failure voltage increased significantly. In addition, the electrothermal efficiency of ceramic/AgNWs@AZO-TCF is significantly improved after sputtering a SiO₂ layer on the surface of ceramic substrate. Compared with ceramic/AgNWs@AZO-TCF, the temperature of ceramic-SiO₂/AgNWs@AZO-TCF increases from 78.7 to 113.2 °C under applied voltage of 6 V, which possess the application scenarios for electrothermal-ceramics teacup (or tableware) to realize the function of heat preservation and disinfection. Full article