Al-doped ZnO Research Articles

High-performance transparent AZO UV photodetectors

In this work, the fabrication of undoped ZnO (ZO) and 3 at.% aluminum (Al) doped ZnO (AZO) thin films (TFs) based transparent photodetectors (PDs) was reported. Both films were spin-coated on fluorine-doped tin oxide (FTO) substrates to investigate the influence of Al doping on the ultraviolet (UV) detection performance of the devices. The systematic characterizations reveal that Al doping positively affects the characteristics of ZO-TFs. The Al doping leads to slight shift in crystalline peaks and induces an enhancement in grain size. In addition, the surface roughness of ZO-TFs gets lower on Al doping. Further, the Al doping improved the transparency and widening of band gap of TFs. The PDs having metal–semiconductor-metal (MSM) configuration were achieved by screen-printing of Ag paste onto ZO and AZO-TFs. The current–voltage (I-V) profiles of the fabricated PDs were measured in the dark and under UV excitation of 365 nm. The AZO-TFs based MSM PD exhibits a spectral responsivity of 326.82 mA/W and an external quantum efficiency of 111.03%. The reproducibility of the fabricated PDs was tested by performing time-dependent photo-response measurements.

<span>Effect of limited oxygen gas flux on properties of Al-doped ZnO films</span>

In this study, Al-doped ZnO thin films were sputter deposited on glass substrate as a function of limited oxygen gas inlet. The crystal structure, optical, and electrical properties of the films were characterized using X-ray diffraction, scanning electron microscopy, UV-Vis spectroscopy, and Hall measurement. High crystallinity was found in all AZO samples. Surface morphology presented small grain size of ~ 50 – 100 nm, and thickness of AZO thin films were maintained approximately at 280 nm. Average optical transmittance of AZO films was about 90% in the 450 – 600 nm region, and optical band-gap values varied from 3.327 to 3.380 eV. The electrical resistivity of AZO films decreased with an increasing amount of oxygen flux. These AZO films are quite appropriate for the perspective development of UV photodetectors as a central role absorbing components or n-type semiconducting layers.

Effect of sputtering power and oxygen partial pressure on structural and opto-electronic properties of Al-doped ZnO transparent conducting oxides

This paper presents the results of electrical, optical and structural properties, along with studies of the surface morphology and cross sections of aluminium-zinc oxide (AZO) thin films. The thin films were fabricated by reactive magnetron sputtering using the two-element Zn-Al disk. The properties of the thin films prepared using different sputtering power densities and different oxygen partial pressures in the working chamber were discussed. To control the partial pressure of oxygen, a characteristic parameter of the magnetron power supply, called the circulating power, was used. The best properties of prepared AZO thin film as a transparent oxide conducting thin film were found for the film prepared using the ratio of circulating to effective power equal to 0.5. For that thin film, the electron concentration of about 6·1020 and the band gap properties (bandgap width equal to 3.14 eV, work function equal to 3.75 eV) were determined.

Strong and Robust Core-Shell Ceramic Fibers Composed of Highly Compacted Nanoparticles for Multifunctional Electronic Skin.

Functional fibers composed of textiles are considered a promising platform for constructing electronic skin (e-skin). However, developing robust electronic fibers with integrated multiple functions remains a formidable task especially when a complex service environment is concerned. In this work, a continuous and controllable strategy is demonstrated to prepare e-skin-oriented ceramic fibers via coaxial wet spinning followed by cold isostatic pressing. The resulting core-shell structured fiber with tightly compacted Al-doped ZnO nanoparticles in the core and highly ordered aramid nanofibers in the shell exhibit excellent tensile strength (316MPa) with ultra-high elongation (33%). Benefiting from the susceptible contacts between conducting ceramic nanoparticles, the ceramic fiber shows both ultrahigh sensitivity (gauge factor = 2141) as a strain sensor and a broad working range up to 70 °C as a temperature sensor. Furthermore, the tunable core-shell structure of the fiber enables the optimization of impedance matching and attenuation of electromagnetic waves for the corresponding textile, resulting in a minimum reflection loss of -39.1dB and an effective absorption bandwidth covering the whole X-band. Therefore, the versatile core-shell ceramic fiber-derived textile can serve as a stealth e-skin for monitoring the motion and temperature of robots under harsh conditions.

Flexible epitaxial LiNbO3 thin film with ferroelectricity and nonlinear optical response

Flexible or wearable devices are of great interests in the modern technologies, and oxide thin films are critical components for such applications. In this work, epitaxial LiNbO3 (LNO) thin film integrated on flexible mica substrate has been achieved. Al-doped ZnO (AZO) layer has been first deposited as buffer layer to obtain the epitaxial LNO film, furthermore AZO serves as bottom electrode for electrical measurement. The as-deposited LNO film exhibits high epitaxial quality with c-direction growth. The transmittance measurement indicates the high transparency of the film, ～85 % in visible range and ～90 % in near infrared region up to 1500 nm. The second harmonic generation (SHG) measurement confirms the nonlinearity of the flexible LNO film. The LNO/AZO/mica film also presents apparent ferroelectric response. Overall, the high-quality LNO integrated on flexible mica could be potentially applied in wearable optical and electrical devices.

Fabrication of alcohol sensor using undoped and Al doped ZnO nanostructure film with polymer electrolyte gating

We report the fabrication of two terminal and three terminal gas sensor using Al-doped ZnO nanostructured-films and polymer electrolyte gate dielectric on glass substrate using vacuum free chemical method. The Al doped ZnO films are characterized by UV–vis Spectrometer, SEM, EDX and XRD. The characterization results have revealed the polycrystalline structure of both undoped and doped ZnO; with loosely packed, porous, and spherical granny nanostructure with mean grain size 20–10 nm and bandgap of the films is within the range of 3.12–3.16 eV. The conductivity of the ZnO film is tuned by Al concentration and the maximum value of conductivity was observed in 3 % Al doped ZnO films. Similarly, the best performance index of TFT such as current ON/OFF ratio, high transconductance and low threshold voltage was observed in 3 % Al doping concentration. The ordinary (two-terminal) sensor and three-terminal (FET) sensors' responses towards three different concentrations 50, 250, 500 ppm of ethanol and methanol vapors have been studied. The sensitivity of the film is modulated by Al concentration and higher value of sensitivity was achieved at 3 % Al doped ZnO films. The use of polymer electrolyte enhanced the sensitivity of the device which is more effective in methanol vapor. The Response-Recovery time of the sensor is significantly improved in three terminal devices than the two terminal devices.

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.

Experimental and DFT investigations of Al-doped ZnO nanostructured thin films

Al doped ZnO thin films at different concentrations have been successfully synthesized, characterized experimentally, and investigated theoretically by density functional theory (DFT). The crystal structure analysis was carried out using X-ray diffraction (XRD) data. Wurtzite structures of a single phase with a preferred orientation along the (002) plane are obtained. The surface morphology has been investigated by atomic force microscopy (AFM) which showed homogeneous and compact surfaces with spherical shape grains that change to a wave like nematic structure with increasing Al doping rate. For a complete characterization, experimental and theoretical analysis of optical and electrical properties have been done using UV–Vis spectrophotometry, the four-probe method, electronic band structure and density of states calculations, and the Boltz-Trap code based on the semi classical theory of Boltzmann. Both, experimental and theoretical, studies indicate an increase in gap energy with high transparency in the visible region and electrical conductivity improvement due to a non-localized state around the Fermi level. The experimental and theoretical studies agree well and show a similar tendency of the results. Therefore, these properties of Al-doped ZnO open a new avenue for optoelectronic and photonic device applications.

Defectivity of Al:ZnO thin films with different crystalline order probed by Positron Annihilation Spectroscopy

Three Positron Annihilation Spectroscopy (PAS) techniques have been employed to investigate the point defects of Al-doped Zinc Oxide (AZO) thin films grown by Radio Frequency (RF) magnetron sputtering with different substrates and deposition parameters. The films were grown with thickness varying from 100 to 300 nm, and their crystalline quality ranged from single crystalline epitaxial to partially amorphous. We found that the main defect in the crystalline samples is the 3VZn−VO four vacancy complex, with a concentration around 1018−1019 cm−3. In polycrystalline films larger vacancy clusters, within 10%−20% of the total concentration, were detected. These vacancy clusters are inferred to be most likely located at the grain boundaries. In partially amorphous films the concentration of these larger vacancy clusters, located either at grain boundaries or in the amorphous regions of the film, approached even the 40%, and also some sub-nano voids have been observed.

Fabrication and analysis of ZnO and Al-doped ZnO films using the SILAR technique

In this study, undoped ZnO and Al-doped ZnO thin films were successfully deposited on ITO substrates at various concentrations using the SILAR method. The deposited thin films underwent characterization via SEM/EDS, XRD, and UV-Vis spectroscopy. XRD analysis revealed that the thin films crystallized at the nanoscale, with crystallization quality varying based on the concentration of Al dopant. SEM/EDS analysis indicated a notable influence of Al doping concentration on the morphology of ZnO thin films. UV-Vis analysis highlighted significant differences in both the optical band gap values and transmittance of the thin films depending on the dopant used.

Record-High Thermoelectric Performance in Al-Doped ZnO via Anderson Localization of Band Edge States.

Oxides are of interest for thermoelectrics due to their high thermal stability, chemical inertness, low cost, and eco-friendly constituting elements. Here, adopting a unique synthesis route via chemical co-precipitation at strongly alkaline conditions, one of the highest thermoelectric performances for ZnO ceramics ( 21.5µW cm-1 K-2 and 0.5 at 1100K in ) is achieved. These results are linked to a distinct modification of the electronic structure: charge carriers become trapped at the edge of the conduction band due to Anderson localization, evidenced by an anomalously low carrier mobility, and characteristic temperature and doping dependencies of charge transport. The bi-dimensional optimization of doping and carrier localization enable a simultaneous improvement of the Seebeck coefficient and electrical conductivity, opening a novel pathway to advance ZnOthermoelectrics.

Improved Specific Contact Resistivity in Amorphous IGZO Transistors Using an ALD-Derived Al-Doped ZnO Interlayer

Improved Specific Contact Resistivity in Amorphous IGZO Transistors Using an ALD-Derived Al-Doped ZnO Interlayer

Enhancement capacitance of FTO electrodes via the electrospun ZnO thin film coating for supercapacitor applications; the role of dopants

The present study aimed to investigate the electrochemical performance of nanostructured ZnO thin films (TFs) on the fluorine-doped tin oxide (FTO) substrate. The pure ZnO TFs, Al-doped ZnO TFs, and Cu-doped ZnO TFs were fabricated using electrospinning and post calcination at 400 °C. The electron microscopy studies revealed that electrospun nanofiber masks changed to dense TFs with an average thickness of 250–290 nm constructed by 10–20 nm connected nanoparticles (NPs). The doping of Al and Cu into ZnO TFs increased the hydrophilicity. Cyclic voltammetry (CV), electrochemical impedance (EIS), charge-discharge profiles, and Mott-Schottky (M − S) analysis were performed on the samples to evaluate the capacitance performance of pure and doped ZnO TFs. The semiconductor of TFs was n-type. The results confirm that all films can be used as a supercapacitor. Also, our results suggest that Cu-doped ZnO (CZO) TFs are the best choice for a supercapacitor electrode due to their 1.14 F cm−2 areal capacitance at 1 mA cm−2 applied current.

Dual-Criteria Decision Analysis by Multiphotonic Effects in Nanostructured ZnO.

Simultaneous interrogation of pump and probe beams interacting in ZnO nanostructures of a two-wave mixing is proposed for dual-path data processing of optical signals by nonlinear optical effects. An enhancement in third-order nonlinear optical properties was exhibited by Al-doped ZnO thin films. Multiphoton absorption and nonlinear refraction were explored by the z-scan technique at 532 nm with nanosecond pulses. The evolution of the optical Kerr effect in the ZnO thin films was analyzed as a function of the incorporation of Al in the sample by a vectorial two-wave mixing method. Electrical and photoconductive effects were evaluated to further characterize the influence of Al in the ZnO solid samples. Potential applications of nonlinear optical parameters for encoding and encrypting information in light can be envisioned.

Orientation-dependent Electrical and Optical Characteristics of non-epitaxial Al-doped ZnO thin films

Based on the theory of crystal anisotropy, it is proposed to improve electrical and optical performance by adjusting the orientation growth of Al-doped ZnO thin films. AZO thin films with preferred (002) and (103) orientation were deposited by stress regulation in the magnetic control sputtering system. The electrical and optical performance for (002) and (103) preferred thin films with identical texture strength and film thickness were analysed in detail. Compared to the conventional (002) preferred AZO thin films, (103) preferentially oriented AZO films exhibit lowering 34.2 % resistivity at the cost of reducing 2.1 % visible light transmittance. XPS fitting analysis of the O1s peak reveals that differences in oxygen vacancy concentration between the two orientations are primarily responsible for variations in electrical properties. It's a promising method by adjusting the orientation growth to improve electrical and optical performance of AZO thin films.

Underlying mechanism of Al incorporation in sol-gel-based dip-coated ZnO:Al thin films

Al-doped ZnO films were applied to glass substrates using a sol-gel-based dip-coating method. The chemical composition, surface morphology, crystal structure, and optical and electrical properties were examined to elucidate the mechanism underlying doping efficiency. The optimum Al-doping was 1.00 at%. Al doping induced an increase in the crystallite size, light transmission, optical band gap energy, and carrier concentration but decreased the resistivity of the films. Excessive doping level beyond 1.00 at% degraded all the characteristics of the films. The underlying mechanism of the Al dopant atoms in the ZnO lattice is related to the growth units. The addition of aluminum nitrate promoted the formation of Zn(OH)2 growth units in the solution, whereas its further addition resulted in the formation of additional Zn(OH)2, along with the Zn(OH)42−. The deterioration in the characteristics of the films was attributed to the Zn(OH)42− formation. Understanding the relation between the film characteristics and growth-unit formation is a base tool to increase the optimum Al-doping level, improving film application towards high performance of optoelectronic devices.

A bifunctional strategy enabling 4.55 V LiCoO2 with improved electrochemical performance

LiCoO2 (LCO) has been functionally modified with electronic conductor of Al doped ZnO (AZO) and ionic conductor of Li3PO4 (LPO). The physicochemical characterization results demonstrated that the hexagonal structured AZO small crystal particles epitaxial growth formed island-like structures on the surface of LCO particles and LPO filled on the surface of remaining exposed LCO particles. Due to the unique composite coating layer with excellent electronic conductivity and Li ion conductivity, the AZO and LPO coated LCO exhibits outstanding rate capability and cycle stability in the voltage range of 2.75–4.55 V. The modified LCO delivered a specific capacity 206 mA h g−1 at 0.5C rate (100 mA g−1), and the capacity retention was 91.7 % after 50 cycles, which was a remarkable improvement comparing with uncoated LCO (34.8 %). Moreover, it exhibited an outstanding rate property, maintaining a discharge capacity of 161.4 mA h g−1 at 4C. This bifunctional strategy with AZO and Li3PO4 is an efficient approach to improve the electrochemical performance of LCO at high cut-off voltage (>4.5 V).

Structural, electrostatic force microscopy, work function, and optical characterization of pure and Al-doped ZnO nanoparticles

The electrical and optical characteristics of pure and Al-doped zinc oxide (ZnO) nanoparticles were analyzed. The work function of these nanoparticles was investigated using Kelvin Probe Force Microscopy (KPFM). The work function of the Al-doped ZnO nanoparticles was found to be lower than that of undoped ZnO nanoparticles. Electrostatic Force Microscopy (EFM) was employed to map the distribution of charges and conductivity in both ZnO and Al -doped ZnO, revealing enhanced charge trapping and increased conductivity in the Al-doped ZnO nanoparticles compared to the undoped ones. XRD analysis verified that both pure ZnO and Al-doped ZnO nanoparticles exhibited a hexagonal wurtzite crystal structure. Additionally, Raman spectroscopy revealed new vibrational modes at 572 cm−1, which were attributed to E1 (LO) in Al-doped ZnO. UV–visible spectroscopy indicated that the band gap of Al -doped ZnO nanoparticles is wider than that of pure ZnO nanoparticles, Additionally, photoluminescence spectroscopy demonstrated a blue shift in the emission spectrum of the Al-doped ZnO nanoparticles, accompanied by a reduction in green emission defects.

Improved performance in quantum-dot light-emitting diodes through current annealing

The impact of metallic diffusion, stemming from the thermal evaporation process of electrodes, exerts a substantial influence on solution-processed quantum-dot light-emitting diodes (QD-LEDs). This study highlights a significant enhancement in the performance of QD-LEDs achieved through post-metal-evaporation current annealing. The choice of different metal electrodes emerges as a critical factor affecting QD-LED performance during current annealing. In the case of red QD-LEDs with an Al cathode, the maximum external quantum efficiency (EQE) surged from 7.0% to an impressive 14.1%. Conversely, QD-LEDs with an Ag cathode exhibited a more modest improvement, progressing from 10.8% to 12.4%. Notably, an Al/Ag composite electrodes demonstrated the potential for further enhancement, achieving a remarkable maximum EQE of 18.3%. The observed performance improvements can be attributed to the formation of metal diffusion-induced Al-doped ZnO, facilitating electron injection, and Al-oxidized passivated quantum dots (QDs), effectively mitigating metal-induced quenching following current annealing. This study conclusively demonstrates that the application of current annealing can effectively counteract the adverse effects of metal diffusion in QD-LEDs, presenting itself as a promising method for elevating the overall performance of quantum-dot light-emitting diodes.

Study the characterization of ZnO and AZO films prepared by spray pyrolysis and the effect of annealing temperature

Spray-pyrolysis was used to successfully create ZnO and AZO (Al-doped ZnO) thin films on glass substrates at various annealing temperatures. Structure, morphology, and optical characteristics were investigated in relation to doping and annealing temperature using analytical techniques such as FTIR, UV–Vis spectroscopy, XRD, and FE-SEM. The films' singular-phase polycrystalline hexagonal Würtzite structure was revealed by XRD data, and the crystallographic plane for both AZO and ZnO was (0 0 2). Crystallite sizes are increased by raising the annealing temperature and adding Al-doping, which enhances surface morphology. where the diameters of the AZO crystallites expanded from 23.3 to 33.3 nm, whereas the ZnO crystallites grew from 27.8 to 28.5 nm. Scanning electron microscopy's morphology reveals that the surface particles' tiny, round shapes have changed to spherical clusters that resemble cauliflowers with increasing annealing temperatures. Notably, the ZnO film has a high transmittance, whereas the AZO film has a relatively low transmittance. Furthermore, at an annealing temperature of 400 °C, all films show notable absorbance, with the highest absorption seen at 400 and 413 nm for ZnO and AZO, respectively. The bandgap values at various annealing temperatures vary from 3.22 to 3.23 eV and 3.08–3.12 eV for ZnO and AZO, respectively. As the annealing temperature rose, the phenomena showed a drop in value.