A wet chemical preparation of transparent conducting thin films of Al-doped ZnO nanoparticles

A wet chemical deposition method for preparing transparent conductive thin films on the base of Al-doped ZnO (AZO) nanoparticles has been demonstrated. AZO nanoparticles with a size of 7 nm have been synthesised by a simple precipitation method in refluxed conditions in ethanol using zinc acetate and Al-isopropylate. The presence of Al in ZnO was revealed by the EDX elemental analysis (1.8 at.%) and UV–Vis spectroscopy (a blue shift due to Burstein–Moss effect). The obtained colloid solution with the AZO nanoparticles was used for preparing by spin-coating thin films on glass substrates. The film demonstrated excellent homogeneity and transparency (T > 90%) in the visible spectrum after heating at 400 °C. Its resistivity turned to be excessively high (ρ = 2.6 Ω cm) that we ascribe to a poor charge percolation due to a high film porosity revealed by SEM observations. To improve the percolation via reducing the porosity, a sol–gel solution was deposited “layer-by-layer” in alternation with layers derived from the AZO colloid followed by heating. As it was shown by optical spectroscopy measurements, the density of thus prepared film was increased more than twice leading to a significant decrease in resistivity to 1.3 × 10⁻² Ω cm.     

掺杂透明导电半导体薄膜的光电性能研究

掺杂氧化锌透明导电膜(AZO)是一种重要的光电子信息材料，其制备方法有真空蒸镀法、磁控溅射法，化学气相沉积和脉冲激光沉积法等。该文采用溶胶 凝胶（sol gel)工艺在普通玻璃基片上成功地制备出Al3+掺杂型ZnO透明导电薄膜。将这种薄膜在空气和真空中以不同的温度进行了退火处理，并对薄膜进行了XRD分析和光电性能研究。结果表明，所制备的薄膜为钎锌矿型结构，在c轴方向择优生长，真空退火有利于薄膜结晶状况的改善，并使薄膜的载流子浓度大幅度地增加而电阻率下降，并且真空退火对薄膜的透射率影响不大。     

Room-temperature deposition of transparent conducting Al-doped ZnO films by RF magnetron sputtering method

Transparent conductive Al-doped zinc oxide (AZO) films with highly (0 0 2)-preferred orientation were deposited on quartz substrates at room temperature by RF magnetron sputtering. Optimization of deposition parameters was based on RF power, Ar pressure in the vacuum chamber, and distance between the target and substrate. The structural, electrical, and optical properties of the AZO thin films were investigated by X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The 250 nm thickness AZO films with an electrical resistivity as low as 4.62 × 10⁻⁴ Ω cm and an average optical transmission of 93.7% in the visible range were obtained at RF power of 300 W, Ar flow rate of 30 sccm, and target distance of 7 cm. The optical bandgap depends on the deposition condition, and was in the range of 3.75-3.86 eV. These results make the possibility for light emitting diodes (LEDs) and solar cells with AZO films as transparent electrodes, especially using lift-off process to achieve the transparent electrode pattern transfer.     

The ultraviolet photoconductive detector based on Al-doped ZnO thin film with fast response

We report fabrication and characterization of metal-semiconductor-metal photoconductive detectors based on Al-doped ZnO thin films fabricated by radio frequency magnetron sputtering.Optical and structural properties of the thin films were characterized using various techniques.At 6 V bias,a responsivity higher than 4 A/W in the wavelength shorter than 350 nm was obtained,and this responsibility dropped quickly and reached the noise floor in the visible region.Transient response measurement revealed that the...     

Room-temperature deposition of transparent conductive Al-doped ZnO thin films using low energy ion bombardment

Al-doped zinc oxide (AZO) films are prepared on quartz substrates by dual-ion-beam sputtering deposition at room temperature (∼25°C). An assisting argon ion beam (ion energy E _i =0–300 eV) directly bombards the substrate surface to modify the properties of AZO films. The effects of assisted-ion beam energy on the characteristics of AZO films were investigated in terms of X-ray diffraction, atomic force microscopy, Raman spectra, Hall measurement and optical transmittance. With increasing assisting-ion beam bombardment, AZO films have a strong improved crystalline quality and increased radiation damage such as oxygen vacancies and zinc interstitials. The lowest resistivity of 4.9×10⁻³Ω cm and highest transmittance of above 85% in the visible region were obtained under the assisting-ion beam energy 200 eV. It was found that the bandgap of AZO films increased from 3.37 to 3.59 eV when the assisting-ion beam energy increased from 0 to 300 eV.     

The transparence comparison of Ga- and Al-doped ZnO thin films

The Ga-doped ZnO (GZO) and Al-doped ZnO (AZO) thin films were grown on quartz glass substrates by pulsed laser deposition under different oxygen partial pressures (PO₂). The transparent performances of films versus properties of structure and conductivity were discussed. With the increase of PO₂, the transmittance of both GZO films and AZO films increased to maximum and then decreased which were in according with the change of crystallization quality. The transmittance of GZO films was higher than that of AZO films, which were not dominated by the impurity ions induced by doping. AFM images and surface roughness mean square coefficients showed that the surfaces of GZO films were smoother than that of AZO films, which were due to the dopant Ga acting as the surfactant and smoothed the GZO films surface.     

Growth of transparent conducting nano-structured In doped ZnO thin films by pulsed DC magnetron sputtering

Transparent conducting nano-structured In doped zinc oxide (IZO) thin films are deposited on corning 7059 glass substrates by bipolar pulsed DC magnetron sputtering with variation of pulsed frequency and substrate temperature. Highly c-axis oriented IZO thin films were grown in perpendicular to the substrate on the 30 kHz and 500 °C. The IZO films exhibited surface roughness of 3.6 nm similar to the commercial ITO and n-type semiconducting properties with electrical resistivity (carrier mobility) of about 5 × 10⁻³ Ω cm (14 cm²/V s). The optical characterization showed high transmittance of over 85% in the UV-vis region and exhibited the absorption edge of near 350 nm. In micro-Raman spectra, the origin of two additional modes is attributed to the host lattice defect due to the addition of In dopant. These results suggest that the IZO film can possibly be applied to make transparent conducting electrodes for flat panel displays.     

Preparation and characterization of La0.5Sr0.5CoO3 /Al-doped ZnO thin film heterojunctions

In this study, p–n heterojunctions with La_0.5Sr_0.5CoO₃ (LSCO) and Al-doped ZnO (AZO) thin films were fabricated by the radio frequency (r.f.) magnetron sputtering technique. The LSCO/AZO heterojunction was obtained by stacking the p-type LSCO thin film on the annealed n-type AZO thin film under different Ar: O₂ sputter gas ratio atmosphere. The thickness of LSCO and AZO thin films are about 400 nm and 500 nm, respectively. Good crystalline match between LSCO and AZO films was observed from the SEM and XRD analysis. The heterojunction diode clearly demonstrated rectifying behavior in the range of ?8 to +8 V in reverse shape. The turn-on voltage of the diodes is obtained around 1.5 V and is in agreement with the value obtained from the difference in the work functions of LSCO and AZO. The band structure of the heterojunction was proposed based on the results of analysis.     

Optical properties of Al-doped ZnO thin films by ellipsometry

Al-doped ZnO thin films (AZO) were prepared on Si (1 0 0) substrates by using sub-molecule doping technique. The Al content was controlled by varying Al sputtering time. The as-prepared samples were annealed in vacuum chamber at 800 °C for 30 min. From the XRD observations, it is found that all films exhibit only the (0 0 2) peak, suggesting that they have c-axis preferred orientation. The average transmittance of the visible light is above 80%. Spectroscopic ellipsometry was used to extract the optical constants of the films. The absorption coefficient and the energy gap were then calculated. The results show that the absorption edge initially blue-shifts and then red-shifts with increase of Al content.     

AlGaN/GaN high-electron-mobility transistors with transparent gates by Al-doped ZnO

AlGaN/GaN high-electron-mobility transistors （HEMTs） with Al-doped ZnO （AZO） transparent gate electrodes are fabricated, and Ni/Au/Ni-gated HEMTs are produced in comparison. The AZO-gated HEMTs show good DC characteristics and Schottky rectifying characteristics, and the gate electrodes achieve excellent transparencies. Compared with Ni/Au/Ni-gated HEMTs, AZO-gated HEMTs show a low saturation current, high threshold voltage, high Schottky barrier height, and low gate reverse leakage current. Due to the higher gate resistivity, AZO-gated HEMTs exhibit a current-gain cutoff frequency （fT） of 10 GHz and a power gain cutoff frequency （fmax） of 5 GHz, and lower maximum oscillation frequency than Ni/Au/Ni-gated HEMTs. Moreover, the C-V characteristics are measured and the gate interface characteristics of the AZO-gated devices are investigated by a C-V dual sweep.     

Green synthesis of silver-graphene nanocomposite-based transparent conducting film

In the present work, silver nanoparticles (Ag NPs)/graphene nanocomposite has been synthesized successfully by simple solvothermal method via green route. Citric acid is used as green reducing agent for the reduction of graphene oxide (GO) and Ag ions. Silver nitrate is used as a precursor material for Ag NPs. As synthesized Ag NPs/graphene nanocomposite has been characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infra-red spectroscopy, UV–vis spectroscopy, thermal gravimetric analysis, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. Experimental results confirm the reduction of GO and the successful formation of Ag NPs decorated graphene nanosheets. In addition, spray coating technique is employed for the fabrication of transparent conducting films. Enhancement in the optoelectrical signatures has been achieved using thermal graphitization of fabricated films. Thermal graphitization at 800 °C for 1 h marks the best performance of fabricated film with sheet resistance of ~3.4 kΩ/□ and transmittance (550 nm) of ~66.40%, respectively.     

纳米晶SnO2透明导电薄膜的研制

阐述了金属氧化物透明导电薄膜研究的发展情况及其应用前景。介绍了采用磁控溅射技术 ,使用混合气体Ar和O2 ,在衬底温度为 15 0～ 40 0℃的耐热玻璃基片上制备纳米晶SnO2 :Sb透明导电薄膜 ,通过测定X射线衍射谱 ,表明薄膜择优取向为 [110 ]和 [2 11]方向。测量了SnO2 :Sb薄膜的导电特性随衬底温度及氧分压的变化。光学特性测量结果表明薄膜具有较高的透过率。     

掺钼ZnO透明导电薄膜的太赫兹电磁波传输性质

采用直流磁控反应溅射方法,通过调节氧分压在玻璃基底上制备了不同载流子浓度的掺Mo的ZnO（ZMO）透明导电薄膜.应用太赫兹电磁波时域光谱技术研究了ZMO导电膜的太赫兹电磁波透射性质及介电响应,得到了与频率相关的电导率、能量吸收和薄膜折射率,实验结果与经典Drude模型相符很好.ZMO导电膜的太赫兹电磁波脉冲透射性质表明,通过调节ZMO薄膜的载流子浓度,该导电膜可作为应用于衬底和光学器件等太赫兹电磁波频率范围的宽带抗反射涂层. 关键词： 太赫兹电磁波光谱 薄膜电导率 宽带抗反射 透明导电薄膜     

A study on the wet etching behavior of AZO (ZnO:Al) transparent conducting film

This paper studies the wet etching behavior of AZO (ZnO:Al) transparent conducting film with tetramethylammonium hydroxide (TMAH). The optimum optoelectronic film is prepared first using designated RF power, film thickness and controlled annealing heat treatment parameters. The AZO film is then etched using TMAH etchant and AZ4620 photoresist with controlled etchant concentration and temperature to examine the etching process effect on the AZO film optoelectronic properties. The experimental results show TMAH:H₂O = 2.38:97.62 under 45 °C at the average etch rate of 22 nm/min as the preferred parameters. The activation energy drops as the TMAH concentration rises, while the etch rate increases along with the increase in TMAH concentration and temperature. After lithography, etching and photoresist removal, the conductivity of AZO film dramatically drops from 2.4 × 10⁻³ Ω cm to 3.0 × 10⁻³ Ω cm, while its transmittance decreases from 89% to 83%. This is due to the poor chemical stability of AZO film against AZ4620 photoresist, leading to an increase in surface roughness. In the photoresist postbaking process, carbon atoms diffused within the AZO film produce poor crystallinity. The slight decreases in zinc and aluminum in the thin film causes a carrier concentration change, which affect the AZO film optoelectronic properties.     

Deposition of quasi-crystal Al-doped ZnO thin films for photovoltaic device applications

Quasi-crystal aluminum-doped zinc oxide (AZO) films were prepared by in situ radio frequency (RF) magnetron sputtering (sputtering without annealing) on glass substrates. The influence of deposition parameters on the optoelectronic and structural properties of the in situ deposited quasi-crystal AZO films was investigated in order to compare resulting samples. X-ray diffraction (XRD) patterns show that the quasi-crystal AZO thin films have excellent crystallization improved with increase of the RF power and substrate temperature, with an extremely preferential c-axis orientation exhibit sharp and narrow XRD pattern similar to that of single-crystal. Field emission scanning electron microscopy (FESEM) images show that quasi-crystal AZO thin films have uniform grains and the grain size increase with the increase of RF power and substrate temperature. Craters of irregular size with the columnar structure are observed in the quasi-crystal AZO thin films at a lower substrate temperature while many spherical shaped grains appeared at a higher substrate temperature. The average optical transmittance of all the quasi-crystal AZO films was over 85% in the 400-800 nm wavelength range. The resistivity of 4.176 × 10⁻⁴ Ω cm with the grain size of 76.4891 nm was obtained in the quasi-crystal AZO thin film deposited at 300 °C, under sputtering power of 140 W.     

Laser-induced lateral voltage in epitaxial Al-doped ZnO thin films on tilted sapphire

Laser-induced voltage effects in epitaxial Al-doped ZnO thin films on tilted sapphire have been experimentally studied at room temperature. An open-circuit lateral voltage signal with nanosecond response time was observed when the film surface was irradiated by laser pulses of 308 nm and 1064 nm, and the voltage responsivity of the signal for 308-nm irradiation is much higher than that for 1064-nm irradiation. A mechanism based on the thermoelectric effect is proposed to explain the origin of the laser-induced lateral voltage in this system. The result suggests that the Al-doped ZnO thin films have a potential application in wide-band photodetectors from ultraviolet to near infrared.     

Reversible wettability of nanostructured ZnO thin films by sol-gel method

Nanostructured ZnO thin films were deposited on Si(1 1 1) and quartz substrate by sol-gel method. The thin films were annealed at 673 K, 873 K, and 1073 K for 60 min. Microstructure, surface topography, and water contact angle of the thin films have been measured by X-ray diffractometer, atomic force microscopy, and water contact angle apparatus. XRD results showed that the ZnO thin films are polycrystalline with hexagonal wurtzite structure. AFM studies revealed that rms roughness changes from 2.3 nm to 7.4 nm and the grain size grow up continuously with increasing annealing temperature. Wettability results indicated that hydrophobicity of the un-irradiated ZnO thin films enhances with annealing temperature increase. The hydrophobic ZnO surfaces could be reversibly switched to hydrophilic by alternation of UV illumination and dark storage (thermal treatment). By studying the magnitude and the contact angle reduction rate of the light-induced process, the contribution of surface roughness is discussed.     

The properties of transparent conducting molybdenum-doped ZnO films grown by radio frequency magnetron sputtering

Transparent conducting molybdenum-doped zinc oxide films are prepared by radio frequency(RF) magnetron sputtering at ambient temperature.The MoO3 content in the target varies from 0 to 5 wt%,and each film is polycrystalline with a hexagonal structure and a preferred orientation along the c axis.The resistivity first decreases and then increases with the increase in MoO3 content.The lowest resistivity achieved is 9.2 × 10-4.cm,with a high Hall mobility of 30 cm2.V-1.s-1 and a carrier concentration of 2.3×1020 cm-3 at an MoO3 content of 2 wt%.The average transmittance in the visible range is reduced from 91% to 80% with the increase in the MoO3 content in the target.     

Electrical and optical properties of Al-doped ZnO thin films by sol-gel process

Al-doped ZnO (AZO) thin films oriented along the (0 0 2) plane have been prepared by the sol-gel process and their electrical and optical properties with post-deposition heating temperature were investigated. The preferred c-axis orientation along the (0 0 2) plane was enhanced with increasing post-deposition heating temperature and the surface of the films showed a uniform and nano-sized microstructure. The electrical resistivity of the films decreased from 73 to 22 Ω cm as the post-deposition heating temperature increased from 500 to 650 °C; however, the film postheated at 700 °C increased greatly to 580 Ω cm. The optical transmittance of the films postheated below 650 °C was over 86%, but it decreased at 700 °C. The electrical and optical properties of the AZO films with post-deposition heating temperature are discussed.