Papers by Keyword: Al-Doped ZnO

Abstract: The effects of Al doping to the thermoelectric properties of ZnO thin films fabricated through ink-jet printing were studied in this paper. Ink-jet printing was used to deposit the Al doped ZnO thin films. A minimum of 50 print cycles was required to obtain continuous film with approximately 9 μm thick thin films. It was possible to obtain high thermoelectric properties of ZnO by controlling the ratios of dopant added and the temperature of the heat treatments.The XRD traces of Al doped ZnO exhibit a polycrystalline hexagonal structure for the wurtzite phase of ZnO. There were no additional phase detected for Al doped ZnO thin films with increasing amount of Al dopants and heat treatment temperature. The results show Al doping had improved the thermoelectric properties of ZnO with an increased in electrical conductivity. The electrical conductivity of pure ZnO thin film (5 S/cm) was enhanced with increasing the dopant to 4wt% Al doped ZnO (114 S/cm). Negative Seebeck values were observed for all the samples that indicated n-type semiconductor. Pure ZnO samples have a measured Seebeck coefficient-17.63 μV/K decreased to-14.35 μV/K with 4 wt% Al doped.

Abstract: Electrochemical deposition of Al-doped ZnO (AZO) on the ITO glass was investigated in baths containing various concentrations of aluminum nitrate. The electrochemical and chemical reactions can be deduced by means of investigating cathodic polarization curves and time/electroplating-current curves for further characterizing structures of ZnO and AZO, and establishing growth mechanism. High-quality AZO nanorods, depositing on ITO substrate that coated with ZnO seed-layer, were utilized the electrochemical method at-1.0 V (against a reference electrode of Ag/AgCl in 3.0M KCl) in the bath of 90 °C. After annealing at 350 °C, ZnO and AZO nanorods were analyzed by field-emission scanning electron microscope (FESEM) to explore the morphology of nanostructure. The SEM image displayed that the lower Al³⁺ concentrations (20 ~ 60 μM) in the bath, the average diameter of nanorods decreased; while the Al³⁺ concentrations excessed over 60 μM, the morphology of the AZO nanorods turned into partial-area nanosheets instead of the nanorods spread. The crystal structure of the AZO nanorods were identified by using grazing-incident X-ray diffraction (GIXRD). The patterns of the Al³⁺ ions in the range of 20 ~ 60 μM in the bath showed that the preferred orientations were along with the [002] direction which confirmed the result of AZO nanorods well aligned in c-axis orientation, and the characterized peak (002) slightly shifted to the right suggested that Al atoms had doped into the ZnO lattice. We also adopted the X-ray photoelectron spectroscopy to characterize the elemental and chemical compositions of the AZO nanorods. XPS spectrums confirmed that the Al atoms successfully doped. Finally, for identifying the optimal boundary condition of Al content in ZnO, the nanorods with various Al concentrations were utilized via dye-sensitized solar cells (DSSC) experiment with the standard solar Simulators (AM1.5G) and J-V Measurement. We found that the AZO nanorods as the photoanode contained 2.84 at.% Al (60 μM aluminum nitrate in the bath) which performed the highest fill-factor (0.53) and the maximum efficiency (0.41%).

Abstract: The effect of Al doping to the band structure of ZnO was studied in this paper. The electronic band structure of Al doped ZnO was determined by using first-principles based on density functional theory. ABINIT was used to perform the band structure calculation. The calculated band structure of ZnO and Al doped ZnO shows that ZnO is a direct band gap semiconductor. The band structure become narrow with Al doping compared pure ZnO. With Al doping, the band gap of ZnO (0.749 eV) become smaller as the concentration Al doping increased to 4wt% (0.551 eV). The electrical conductivity of Al doped ZnO was studied as a references value for the band gap. The electrical conductivity of ZnO (8.21 S/cm) was enhanced with Al doping increased to 4wt% (71.87 S/cm).

Abstract: The structural and field electeron emission properties of pure and Al doped ZnO nanorods synthesized on the Al substrates using sol-gel method has been studied. Al doping at different levels was achieved by adding Al₂NO₃ at 1, 3 and 5 Al at. % with respect to Zn in the synthesis solution. X-ray analysis shows that all the obtained ZnO nanorods can be indexed to the hexagonal ZnO wurtzite structure. Field electron emission measurement using the nanorods as cathode gave a trend of decreasing turn-on field values with increasing Al-doping levels, with values of 7.2 V/μm, 6.6 V/μm, 6.0 V/μm and 5.8V/μm for pure ZnO nanorods, 1, 3 and 5 at% Al-doped ZnO nanorods, respectively. The F-N plot has a linear relationship and the field enhancement factor for all samples has been obtained.

Abstract: Al-doped ZnO thin films were prepared by ink-jet printing and their electrical and thermal properties with different amounts of Al doping and sintering atmosphere were investigated. The XRD traces of films show the doped materials did not form additional crystalline phases with increasing amounts of Al doping. Electrical conductivity of film increased from 4.86 S/cm to 120.94 S/cm as the amounts of Al doping increased from 0 wt% to 4 wt%. However, the thermal conductivity decreased from 24 W/mK to 13 W/mK with increasing the Al doping from 0 wt% to 4 wt%. The electrical conductivity of film shows higher values sintered in vacuum (120.94 S/cm) compared to film sintered in air (114.1 S/cm).

Abstract: Al-doped ZnO (AZO) powers with a novel rice-like morphology have been successfully synthesized through a simple and efficient hydrothermal approach, the products have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with an energy-dispersive X-ray analyzer and transmission electron microscopy (TEM). It showed that all the samples presented an hexagonal wurtzite structure of high crystallinity, and the microstructure was composed of numerous dumbbells. Furthermore, the heater gas sensors were fabricated and an investigation of gas sensing properties has been conducted. The sensors showed good selectivity to ethanol comparing with NH₃, SO₂, CO and HCHO and possible mechanism was discussed. The Sensors based AZO powers exhibited high response values, reproducible response-recovery to ethanol 50-1800 ppm at 332°C.

Abstract: Different doping concentration Al-doped ZnO nanofibers were synthesized by Atom Layer Deposition (ALD) using PVP fibers as template. The influence of Al doping concentration on the structure and optical properties of nanofibers was investigated. The samples were characterized by means of X-ray diffraction spectra, field emission scanning electron microscopy (FESEM). After doping, the morphologies were not changed, only the diameters of Al-doped ZnO nanofibers became larger. Compared with undoped ZnO, the intensity of diffractive peaks of Al-doped ZnO nanofibers became weak with the increasing of the doping concentration due to stress generation in the crystallization process. In raman spectra, Al₂O₃ peak related peaks were also observed. In addition, the intensity of UV emission decreased with increasing Al doping concentration and had a red shift.

Abstract: In this research, we prepared aluminium (Al)-doped ZnO nanorod arrays on the glass substrate using sonicated sol-gel method. These nanorod arrays were annealed at 500 °C in air and oxygen environment using thermal furnace. Field emission scanning electron microscopy (FESEM) image reveals that nanorod arrays were deposited vertically aligned on the substrate. The stress characteristics of air-annealed and oxygen-annealed Al-doped ZnO nanorod arrays were investigated using Raman spectroscopy and X-ray diffraction (XRD) measurement. The electrical properties of the samples were investigated using two-probe current-voltage (I-V) measurement system. The results show that annealing atmospheres greatly influenced the stress and electrical properties of the nanorod arrays.

Abstract: In this research, we fabricated UV photoconductive sensor using aluminium (Al)-doped ZnO nanorod-nanoflake network thin film. These nanostructures were deposited on the seed-layer-coated glass substrate using sonicated sol-gel immersion method. By using Al contacts, it was found that the performance of the UV photoconductive sensor is very good. The responsivity of the device was 46.4 mA/W with sensitivity of 17.5 under 365-nm UV light (5 mW/cm²) at bias voltage of 10 V. Our study revealed that these nanostructures are very promising material for the UV photoconductive sensor applications.

Abstract: Transparent conducting aluminum-doped zinc oxide (AZO) films with different film thickness had been prepared on soda-lime glass substrates by radio frequency magnetron sputtering using a high density ceramic target. The structural, morphology, electrical, and optical properties of the AZO thin films were investigated by X-ray diffraction, scanning electron microscope, Hall-effect measurement and optical transmission spectroscopy, which were strongly influenced by film thickness. With the film thickness increasing from 140 nm to 710 nm, the resistivity decreases from 9.78 × 10³ to 3.23 × 10³ Ω.cm and an average optical transmission decreases from 88% to 80% in the visible range and the optical bandgap decreases from 3.47 to 3.24 eV.