Search Results (715)

Laser annealing of oxide functional thin films makes them compatible with substrates of various types, especially flexible materials. The effects of optical annealing on Ni-doped ZnO thin films were the subject of investigation and analysis in this study. Using pulsed laser deposition, we deposited polycrystalline ZnNiO films on sapphire and silicon substrates. The deposited film was annealed by laser heating. A continuous CO₂ laser was used for this purpose. The uniformly distributed long-wavelength radiation of the CO₂ laser can penetrate deeper from the surface of the thin film compared to short-wavelength lasers such as UV and IR lasers. After growth, optical post-annealing processes were applied to improve the conductive properties of the films. The crystallinity and surface morphology of the grown films and annealed films were analyzed using SEM, and their electrical parameters were evaluated using van der Pauw effect measurements. We used electrical conductivity measurements and investigated the photovoltaic properties of the ZnNiO film. After CO₂ laser annealing, changes in both the crystalline structure and surface appearance of ZnO were evident. Subsequent to laser annealing, the crystallinity of ZnO showed both change and degradation. High-power CO₂ laser annealing changed the structure to a mixed grain size. Surface nanostructuring occurred. This was confirmed by SEM morphological studies. After irradiation, the electrical conductivity of the films increased from 0.06 Sm/cm to 0.31 Sm/cm. The lifetime of non-equilibrium charge carriers decreased from 2.0·10⁻⁹ s to 1.2·10⁻⁹ s. Full article

Recently, with the development of automation technology in various fields, much research has been conducted on infrared photodetectors, which are the core technology of LiDAR sensors. However, most infrared photodetectors are expensive because they use compound semiconductors based on epitaxial processes, and they have low safety because they use the near-infrared (NIR) region that can damage the retina. Therefore, they are difficult to apply to automation technologies such as automobiles and factories where humans can be constantly exposed. In contrast, short-wavelength infrared photodetectors based on PbS QDs are actively being developed because they can absorb infrared rays in the eye-safe region by controlling the particle size of QDs and can be easily and inexpensively manufactured through a solution process. However, PbS QDs-based SWIR photodetectors have low chemical stability due to the electron/hole extraction layer processed by the solution process, making it difficult to manufacture them in the form of patterning and arrays. In this study, bulk NiO and ZnO were deposited by sputtering to achieve uniformity and patterning of thin films, and the performance of PbS QDs-based photodetectors was improved by optimizing the thickness and annealing conditions of the thin films. The fabricated photodetector achieved a high response characteristic of 114.3% through optimized band gap and improved transmittance characteristics. Full article

Gallium oxide (Ga₂O₃), as a wide-bandgap semiconductor material, is highly expected to find extensive applications in optoelectronic devices, high-power electronics, gas sensors, etc. However, the photoelectric properties of Ga₂O₃ still need to be improved before its devices become commercially viable. As is well known, doping is an effective method to modulate the various properties of semiconductor materials. In this study, Zn–N co-doped Ga₂O₃ films with various doping concentrations were grown in situ on sapphire substrates by atomic layer deposition (ALD) at 250 °C, followed by post-annealing at 900 °C. The post-annealed undoped Ga₂O₃ film showed a highly preferential orientation, whereas with the increase in Zn doping concentration, the preferential orientation of Ga₂O₃ films was deteriorated, turning it into an amorphous state. The surface roughness of the Ga₂O₃ thin films is largely affected by doping. As a result of post-annealing, the bandgaps of the Ga₂O₃ films can be modulated from 4.69 eV to 5.41 eV by controlling the Zn–N co-doping concentrations. When deposited under optimum conditions, high-quality Zn–N co-doped Ga₂O₃ films showed higher transmittance, a larger bandgap, and fewer defects compared with undoped ones. Full article

This study presents the influence of pH control agents and pH value on the physical properties of ZnO thin films obtained by chemical bath deposition. ZnO thin films were synthesized on glass substrates using precursor solutions of different pHs prepared from two bases: sodium hydroxide (NaOH) and ammonia (NH₃). The effect of pH values on the morphological, structural, and optical properties of ZnO thin films was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and UV–Visible spectroscopy. XRD results showed that all the synthesized ZnO thin films are polycrystalline and crystallize in a hexagonal wurtzite structure. The crystallite size, calculated using the Debye–Scherrer formula, varied from 10.50 nm to 11.69 nm for ZnO thin films obtained with NH₃ and from 20.79 nm to 27.76 nm for those obtained with NaOH. FTIR analysis confirmed the presence of functional groups. SEM images indicated that not only the base but also the pH affects the morphology of the films, giving rise to different granular shapes. Overall, the ZnO thin films obtained with NaOH looked more mesoporous compared to those obtained with NH₃. Optical characterization results showed that whatever the base used, the pH of the precursor solution affected the ZnO thin film transmittance. Films synthesized with NH₃ exhibited the best transmittance (80%) at pH 8.5, while the best transmittance (81%) of films synthesized with NaOH was obtained at pH 8 in the visible region. Based on optical and morphological properties, ZnO films obtained from NH₃ at pH 8.5 are found to be more suitable as photoanodes in dye-sensitized solar cells. Full article

This research examines the effect of annealing temperature on the growth orientation of zinc oxide (ZnO) nanorods and its subsequent influence on NO₂ gas sensing efficiency. Zinc oxide (ZnO) nanorods were synthesized using the chemical bath deposition method, followed by annealing at 300, 400, and 500 °C. Diffraction analysis confirmed that both non-annealed and annealed ZnO nanorods crystallize in a hexagonal wurtzite structure. However, increasing the annealing temperature shifts the growth orientation from the c-axis (002) toward the (100) and (101) directions. Microscopy images (FE-SEM) revealed a reduction in nanorod diameter as the annealing temperature increases. Optical characterization using UV–visible and photoluminescence spectroscopy indicated shifts in the band gap energy and emission properties. Contact angle measurements demonstrated the hydrophobic nature of the films. Gas sensing tests at 200 °C revealed that the ZnO thin film annealed at 400 °C achieved the highest NO₂ response of 5.88%. The study highlights the critical role of annealing in modifying the crystallinity, growth orientation, and defect states of ZnO thin films, ultimately enhancing their NO₂ detection capability. 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

Artificial photoelectric synapses exhibit great potential for overcoming the Von Neumann bottleneck in computational systems. All-inorganic halide perovskites hold considerable promise in photoelectric synapses due to their superior photon-harvesting efficiency. In this study, a novel wavy-structured CsPbBr₃/ZnO hybrid film was realized by depositing zinc oxide (ZnO) onto island-like CsPbBr₃ film via atomic layer deposition (ALD) at 70 °C. Due to the capability of ALD to grow high-quality films over small surface areas, dense and thin ZnO film filled the gaps between the island-shaped CsPbBr₃ grains, thereby enabling reduced light-absorption losses and efficient charge transport between the CsPbBr₃ light absorber and the ZnO electron-transport layer. This ZnO/island-like CsPbBr₃ hybrid synaptic transistor could operate at a drain-source voltage of 1.0 V and a gate-source voltage of 0 V triggered by green light (500 nm) pulses with low light intensities of 0.035 mW/cm². The device exhibited a quiescent current of ~0.5 nA. Notably, after patterning, it achieved a significantly reduced off-state current of 10⁻¹¹ A and decreased the quiescent current to 0.02 nA. In addition, this transistor was able to mimic fundamental synaptic behaviors, including excitatory postsynaptic currents (EPSCs), paired-pulse facilitation (PPF), short-term to long-term plasticity (STP to LTP) transitions, and learning-experience behaviors. This straightforward strategy demonstrates the possibility of utilizing neuromorphic synaptic device applications under low voltage and weak light conditions. Full article

Kesterite (CZTS/CZTSSe) thin-film solar cells are considered an eco-friendly, earth-abundant, and low-cost photovoltaic technology that can fulfill our future energy needs. Due to its outstanding properties including tunable bandgap and high absorption coefficient, the power conversion efficiency (PCE) has reached over 14%. However, toxic cadmium sulfide (CdS) is commonly used as an n-type buffer layer in kesterite thin-film solar cells (KTFSCs) to form a better p–n junction with the p-type CZTS/CZTSSe absorber. In addition to its toxicity, the CdS buffer layer shows parasitic absorption at low wavelengths (400–500 nm) owing to its low bandgap (2.4 eV). For the last few years, several efforts have been made to substitute CdS with an eco-friendly, Cd-free, cost-effective buffer layer with alternative large-bandgap materials such as ZnSnO, Zn (O, S), In₂Se₃, ZnS, ZnMgO, and TiO₂, which showed significant advances. Herein, we summarize the key findings of the research community using a Cd-free buffer layer in KTFSCs to provide a current scenario for future work motivating researchers to design new materials and strategies to achieve higher performance. Full article

Wearable tactile sensors with high sensitivity can be potentially used to continuously monitoring physiological signals that are closely related to disease diagnosis and health condition tracking. However, the development of such tactile sensors involves a number of challenges, including a series of expensive patterning processes for microstructure manufacturing and addressing the large thickness of the microstructured composite film. Herein, a mold-free approach is presented to develop an ultra-thin ZnO/PEDOT:PSS composite film with flower-like microstructures via a feasible solution process for highly sensitive tactile sensors. The fabricated tactile sensors exhibit a high sensitivity of 4 × 10³ kPa⁻¹ in the pressure range 0–10 kPa, a fast response to various pressures in merits of the hierarchical microstructures on top of the ultra-thin composite films. Thanks to the fascinating performance of the devices, the tactile sensors are demonstrated with the ability to monitor physiological signals, subtle human body motions, and spatial pressure distribution. Full article

This paper presents a cost-effective and versatile pico-dispensing technique as an efficient and straightforward approach for depositing zinc oxide nanoparticle (ZnO—NP) thin films on micromechanical devices (MEMS). Due to its piezoelectric properties, bulk ZnO is commonly used as a material for micro-/nanocantilever actuation. The pico-dispensing process provides precise control over the deposition, allowing uniform and localized application of ZnO—NP on microcantilevers. Compared to traditional ZnO deposition techniques (e.g., sputtering or sol–gel), pico-dispensing of ZnO—NP offers advantages in simplicity, reduced material waste, and significantly lower costs. Furthermore, it is easy to tailor the composition and properties by incorporating nanoparticles of other materials. Experimental results demonstrate that ZnO—NP thin films deposited via pico-dispensing enable actuation with amplitudes of several nanometers and bandwidths up to 250 kHz, making them potentially suitable for actuation of micromechanical devices such as in dynamic AFM modes. Full article

This study developed a transparent NO₂ gas sensor with enhanced sensing performance and high optical transmittance. Al-doped ZnO thin films were deposited by atomic layer deposition, which was chosen for its capability to precisely control surface chemistry at the atomic scale. Oxygen vacancies were effectively introduced by utilizing trimethylaluminum, a strongly reducing Al₂O₃ precursor, thereby increasing carrier concentration and enhancing gas-sensing performance. By adjusting the Al doping level, the optimized device achieved a 50 °C reduction in operating temperature, a 66.2-fold increase in sensitivity at 150 °C, and shortened response and recovery times. The morphology, crystallinity, and elemental distribution were analyzed using transmission electron microscopy, selected area electron diffraction, and energy-dispersive X-ray spectroscopy, while chemical bonding states were investigated via X-ray photoelectron spectroscopy. Optical properties were characterized using UV–visible spectroscopy, confirming an average transmittance of approximately 80% in the visible range. These results demonstrate the promise of transparent oxide gas sensors for integration into next-generation electronics and Internet of Things-based environmental monitoring 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 optical, electrical, and material properties of In–Zn–O (IZO) films were optimized by adjusting the deposition power and annealing temperature. Films deposited at 125 W and annealed at 300 °C exhibited the best performance, with the lowest resistivity (1.43 × 10⁻³ Ω·cm), highest mobility (11.12 cm²/V·s), and highest carrier concentration (4.61 × 10²⁰ cm⁻³). The average transmittance and optical energy gap were 82.57% and 3.372 eV, respectively. The electrical characteristics of amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) using IZO source-drain (S–D) electrodes with various sputtering powers and annealing temperatures were investigated. The optimal sputtering power of 125 W and annealing temperature of 300 °C for the IZO S–D electrodes resulted in the highest field-effect mobility (~12.31 cm²/V·s) and on current (~2.09 × 10⁻⁶ A). This improvement is attributed to enhanced carrier concentration and mobility, which result from the high In/Zn ratio, the larger grain size, and low RMS roughness in the IZO films. The parasitic contact resistance (R_SD) and channel resistance (R_CH) were analyzed using the total resistance method. R_SD decreased with increasing IZO S–D sputtering power, while R_CH reached a minimum at 125 W. Both resistances decreased significantly as the annealing temperature increased from 200 °C to 300 °C. Full article

This study presents the fabrication and characterization of ZnO–CNT composite-based optoelectronic synaptic devices via a sol–gel process. By incorporating various concentrations of CNTs (0–2.0 wt%) into ZnO thin films, we investigated their effects on synaptic behaviors under ultraviolet (UV) stimulation. The CNT addition enhanced the electrical and optical performance by forming a p–n heterojunction with ZnO, which promoted charge separation and suppressed recombination. As a result, the 1.5 wt% CNT device exhibited the highest excitatory postsynaptic current (EPSC), improved paired-pulse facilitation, and prolonged memory retention. Learning–forgetting cycles revealed that repeated stimulation reduced the number of pulses required for relearning while extending the forgetting time, mimicking biological memory reinforcement. Energy consumption per pulse was estimated at 16.34 nJ, suggesting potential for low-power neuromorphic applications. A 3 × 3 device array was also employed for visual memory simulation, showing spatially controllable and stable memory states depending on CNT content. To support these findings, structural and optical analyses were conducted using scanning electron microscopy (SEM), UV-visible absorption spectroscopy, photoluminescence (PL) spectroscopy, and Raman spectroscopy. These findings demonstrate that the synaptic characteristics of ZnO-based devices can be finely tuned through CNT incorporation, providing a promising pathway for the development of energy-efficient and adaptive optoelectronic neuromorphic systems. Full article

Synthesis and characterization of undoped and samarium-doped CuO–SnO₂:F thin films using the spray pyrolysis technique are presented. The effect of the samarium doping level on the physical properties of these films was thoroughly analyzed. X-ray diffraction patterns proved the successful synthesis of pure CuO–SnO₂:F thin films, free from detectable impurities. The smallest crystallite size was observed in 6% Sm-doped CuO–SnO₂:F thin films. The 6% Sm-doped CuO–SnO₂films demonstrated an increasedsurface area of 40.6 m²/g, highlighting improved textural properties, which was further validated by XPS analysis.The bandgap energy was found to increase from 1.90 eV for undoped CuO–SnO₂:F to 2.52 eV for 4% Sm-doped CuO–SnO₂:F, before decreasing to 2.03 eV for 6% Sm-doped CuO–SnO2:F thin films. Photoluminescence spectra revealed various emission peaks, suggesting a quenching effect. A numerical simulation of a new solar cell based on FTO/ZnO/Sm–CuO–SnO₂:F/X/Mo was carried out using Silvaco Atlas software, where X represented the absorber layer CIGS, CdTe, and CZTS. The results showed that the solar cell with CIGS as the absorber layer achieved the highest efficiency of 15.98. Additionally, the thin films demonstrated strong photocatalytic performance, with 6% Sm-doped CuO–SnO₂:F showing 86% degradation of ampicillin after two hours. This comprehensive investigation provided valuable insights into the synthesis, properties, and potential applications of Sm-doped CuO–SnO₂ thin films, particularly for solar energy and pharmaceutical applications. Full article