Properties Of Aluminum-doped Zinc Oxide Thin Films Research Articles

Influence of power ramps on the physical properties of AZO thin films deposited at room temperature by RF magnetron sputtering technique

Abstract Aluminum-doped zinc oxide (AZO) thin films were deposited on glass substrates at room temperature by RF sputtering technique. Power ramps between 125 and 105 W were applied with a step of 4 W by intervals of 15, 7.5 and 1.8 min, for 180 min at 1.60 Pa. In this study, we investigated the structural, morphological, electrical, and optical properties of AZO films. X-ray Diffraction analysis showed that the films have a wurtzite-type hexagonal crystalline structure with a preferential crystallographic orientation (002) normal to the c axis. The average transmittance is greater than 76% for the wavelength range in the visible spectrum. The bandgap values were found between 3.32 and 4.01 eV, and refractive index was 1.79–2.60. Atomic force microscope measurements show homogeneous films with a roughness between 17–22 nm. A minimum resistivity value of 2.0 × 10−3 Ω cm was obtained for the film by using a power ramp of 4 W/1.8 min.

Properties of AZO thin films prepared by stationary and rotating RF magnetized plasma sputtering source

The aluminum-doped zinc oxide (AZO) films were deposited with a star-shaped plasma using a high-density radio frequency (RF) magnetized sputtering source to develop well-consistent target utilization. The deposited AZO film characteristics were investigated using stationary and rotational modes with a velocity of 40 rpm, Ar pressure of 1.0 Pa, and RF power of 40 W with a deposition time of 1.0 h. The deposition rate profile of stationary mode with a roughness of ±30.18% was more fluctuating than that of rotational mode with a roughness of ±10.90%. The lowest electrical resistivities of the AZO films were obtained as 3.8 × 10−4 and 3.6 × 10−4 Ω cm at r = 0 mm for the stationary and rotational modes, respectively. According to the AFM and SEM results, the surface profile of the rotational mode grown AZO film was more uniform and smoother than that of the stationary mode. The intensity of x-ray diffraction peaks (002) of the grown AZO film was decreased from the center to the edge of the vessel. Most of the films showed two broad Raman peaks at about 274 and 575 cm−1, representing additional mode and longitudinal optical phonons of the wurtzite ZnO crystal. All the AZO films showed a high transmittance in the visible range, and the average transmittance of the AZO films in the visible range was ∼84%.

The physical and optical properties of AZO thin films on teflon substrate at low deposition temperature by spray pyrolysis

<span>This paper presents the physical and optical properties of AZO thin films on Teflon substrate at low deposition temperature by spray pyrolysis. In this study, the effect of different process parameters such as spray time and substrate to nozzle distance on the physical and optical characteristic of aluminium doped zinc oxide (AZO) deposited on Teflon substrates was investigated. The AZO thin films were successfully deposited onto Teflon substrate by spray pyrolysis technique at low deposition temperature. The physical analysis by X-ray diffraction (XRD) shows that the deposited Teflon substrate films have a preferred orientation along the direction (100) and (101). Optical measurements were conducted using Jasco/V-670 Ex Uv-Vis-NIR Spectrophotometer model to confirms that in visible ray it is possible to get good reflectance of AZO films with a reflection of 80%. The values of band gaps Eg were calculated from the spectra of UV-Visible reflectance that were vary between 3.06 and 3.14 eV. </span>

Effect of RF sputtering power and vacuum annealing on the properties of AZO thin films prepared from ceramic target in confocal configuration

Aluminum-doped zinc oxide (AZO) thin films are deposited on glass substrate by radio frequency (RF) magnetron sputtering method in confocal configuration at room temperature (RT). Several techniques are used to investigate the effects of sputtering power, from 50 to 300 W, on structural, optical and electrical properties. It is found, from Grazing Incidence X-Ray Diffraction (GIXRD) analysis, that the sputtering power has a great influence on the crystalline quality of AZO films. A preferential orientation along the c-axis is obtained at lower sputtering power of 50 W. XPS analysis confirms the existence of only Zn and Al in the oxidized state in accordance with the XRD results. SEM and AFM observations of AZO films reveal dense and homogenous distribution of small grains on the surface. Analysis by UV–Vis–NIR spectroscopy at RT reveals that the average optical transmittance in the visible range (400–800 nm) of the AZO thin films is higher than 75%. Hall-effect measurements put into evidence that the electrical resistivity of the films increases with the increase of the sputtering power. A low resistivity of 1.65 × 10−3 Ω cm is obtained for the lowest sputtering power (50W). Moreover, AZO thin film deposited at 50 W and annealed for 1h at 400 °C under vacuum shows a lower resistivity of 5.75 × 10−4 Ω cm, an average optical transmission above 86% and a high figure of merit (ФTC) value of 3.4 × 10−3 Ω−1sq which suggests that the fabricated AZO thin films are promising for optoelectronic devices in the UV region.

Multimode AFM analysis of aluminum-doped zinc oxide thin films sputtered under various substrate temperatures for optoelectronic applications

Here we present an in-depth atomic force microscopy study of aluminum-doped zinc oxide (AZO) thin films utilizing various modes (topology, phase and error signal) together with image processing techniques including skew, kurtosis, entropy, autocorrelation and fractal analysis. Fractal dimension has been calculated via cube counting, triangulation, power spectrum and partitioning methods. A correlation has been found between the micromorphological properties and the functional properties of the AZO transparent conducting oxide when annealed at different temperatures. Structural, electrical, morphological and optical properties of AZO thin films were investigated by XRD, 4-Point-probe, AFM and UV-VIS spectroscopy. The results indicate that the AZO thin film properties are affected by substrate temperature. An optimum figure of merit of 1.518×10−3Ω−1 is obtained for a substrate temperature of 150°C. It is expected that this work can provide a novel approach towards optimization of transparent conducting oxides, in particular with regards to plasmonics.

Pressure effect on structural and electrical properties of AZO thin films annealed in N2/H2 atmosphere

Transparent and conductive aluminum-doped zinc oxide (AZO) thin films were developed using a sol-gel method and annealed in 95 N2/5 H2 forming gas. The pressure effects of forming gas on the structural and electrical properties, and the underlying mechanisms were investigated. XPS analysis reveals that the fraction of the chemisorbed oxygen in the annealed film in 0.01 MPa 95 N2/5 H2 did not exhibit any apparent change compared to the non-annealed films, while the oxygen vacancy content exhibited a remarkable increase. When pressure goes up to 0.03 MPa, significant changes of both the oxygen vacancy concentration and the chemisorbed oxygen content were observed in the annealed films. At 0.03 MPa, the films displayed a perfect orientation along the c-axis and exhibited the lowest resistivity of 1.6 × 10−3 Ω·cm. Our study shows that it is possible to optimize the oxygen distribution and improve the electrical property of AZO film by adjustment of the forming gas pressure.

Effect of substrate rotation speed and off-center deposition on the structural, optical, and electrical properties of AZO thin films fabricated by DC magnetron sputtering

In this study, aluminum-doped zinc oxide (AZO) thin films were deposited by DC magnetron sputtering at room temperature. The distance between the substrate and target axis, and substrate rotation speed were varied to get high quality AZO thin films. The influences of these deposition parameters on the structural, optical, and electrical properties of the fabricated films were investigated by X-ray diffraction (XRD), Raman spectroscopy, spectrophotometry, and four-point probe techniques. The overall analysis revealed that both sample position and substrate rotation speed are effective in changing the optical, structural, and electrical properties of the AZO thin films. We further observed that stress in the films can be significantly reduced by off-center deposition and rotating the sample holder during the deposition. An average transmittance above 85% in the visible range and a resistivity of 2.02 × 10−3 Ω cm were obtained for the AZO films.

Evaluation of the structural, optical and electrical properties of AZO thin films prepared by chemical bath deposition for optoelectronics

Aluminum doped zinc oxide (AZO) thin films for electrode applications were deposited on glass substrates using chemical bath deposition (CBD) method. The influence of deposition time on the structural, morphological, and opto-electrical properties of AZO films were investigated. Structural studies confirmed that all the deposited films were hexagonal wurtzite structure with polycrystalline nature and exhibited (002) preferential orientation. There is no other impurity phases were detected for different deposition time. Surface morphological images shows the spherically shaped grains are uniformly arranged on to the entire film surface. The EDS spectrum confirms the presence of Zn, O and Al elements in deposited AZO film. The observed optical transmittance is high (87%) in the visible region, and the calculated band gap value is 3.27 eV. In this study, the transmittance value is decreased with increasing deposition time. The room temperature PL spectrum exposed that AZO thin film deposited at (60 min) has good optical quality with less defect density. The minimum electrical resistivity and maximum carrier concentration values were observed as 8.53 × 10−3(Ω cm) and 3.53 × 1018 cm−3 for 60 min deposited film, respectively. The obtained figure of merit (ϕ) value 3.05 × 10−3(Ω/sq)- 1 is suggested for an optoelectronic device.

Preparation and characterization of high-transmittance AZO films using RF magnetron sputtering at room temperature

Aluminum-doped zinc oxide (AZO) thin films with 250nm thickness had been prepared on soda-lime glass substrate without heated by RF magnetron sputtering using a ceramic target. The microstructure, surface morphology, electrical and optical properties of AZO thin films had been investigated by X-ray diffraction, scanning electron microscope, four-point probe method and optical transmission spectroscopy. The results indicated that all of the films obtained were polycrystalline with a hexagonal structure and oriented with the c-axis perpendicular to the substrate. The resistivity decreased and transmittance improved with the sputtering power increase. The minimum resistivity of 2.55×10−3Ωcm combined with highest transmittance of 91% was obtained at a sputtering power of 400W. The optical bandgap at different sputtering power varied among 3.81–4.04eV.

Effect of annealing temperature on properties of spin coated AZO films

Transparent conductive aluminium doped zinc oxide (AZO) thin films were prepared on quartz substrates by spin coating method with different annealing temperatures. The structural, electrical and optical properties of AZO thin films were investigated. The AZO thin films had a hexagonal wurtzite structure and the orientation of the sample was along the c-axis, regardless of annealing temperature. Also the modified transmittance of AZO thin films in the visible range (400–800 nm) was over 85%. The experimental results showed that the electrical resistivity of AZO films decreased with increasing annealing temperature from 400 to 500°C but increased with annealing temperature from 500 to 700°C. The lowest electrical resistivity obtained in this study was 1·01 Ω cm for the film annealed at 500°C in oxygen.

Optical and electrical studies of transparent conductive AZO and ITO sputtered thin films for CIGS photovoltaics

AbstractDue to the many advantages of aluminum doped zinc oxide (AZO) as an alternative to indium tin oxide (ITO), the optical and electrical properties of AZO thin films deposited on large substrates by D.C. pulsed magnetron sputtering have been investigated in view of future industrial applications. In order to evaluate the effectiveness of AZO thin films as transparent conductive oxide (TCO), their properties have been compared with those of standard ITO grown with the same technique. The effect of the thickness on the optical properties revealed higher transmittance values for AZO (T>86%) than for ITO (T>83%) films. The best resistivity values obtained for AZO were about 9.7×10–4 Ωcm versus 5.09×10–4 Ωcm measured for ITO films. Moreover, it was observed that the film resistivity is significantly influenced by the working pressure in the case of AZO films while the ITO resistivity appears almost unaffected. Finally, since both the optical and electrical properties are influenced by the film thickness, it was crucial to determine the proper AZO thickness in order to obtain the optimum of electrical and optical properties for the photovoltaic applications. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of the pre-annealing temperature on structural and optical properties of sol–gel deposited aluminium doped zinc oxide

Highly transparent aluminium doped zinc oxide (AZO) thin films were deposited by the sol–gel deposition technique. The effects of various pre-sintering temperatures on the film׳s structural, optical and electrical properties were investigated using scanning electron microscopy, X-ray diffraction spectroscopy, photoluminescence emission measurements, UV–vis spectroscopy and electrical characterization. It was found that the pre-sintering temperature greatly affected the film׳s structural properties and resulted in an almost 100% increase in grain size within the investigated experimental window. Photoluminescence emission and photovoltaic measurements confirmed that the best optoelectronic properties of AZO thin films can be achieved with a pre-sintering temperature of 400°C.

The effects of the aluminium concentration on optical and electrical properties of AZO thin films as a transparent conductive layer

In this paper, we studied the effects of the aluminium dopant concentration on the optical and electrical properties of aluminium doped zinc oxide (AZO) thin films grown on soda-glass substrates by a simple chemical method. The amount of aluminium in the compound was varied from 0 to 5 atomic percent (at.%), and the typical thickness of the films produced was about 300 nm. The thin films were characterized by scanning electron microscopy and X-ray diffraction to investigate the morphology and crystallinity of the samples. The optical properties of the thin films were studied by UV–Vis spectroscopy to determinate absorption, transmittance, and the diffuse reflectance. In addition, the photoluminescence properties of the thin films, excited with a 320 nm UV laser beam, were investigated. The effects of the aluminium concentration on these optical properties are discussed. The films with 2 and 5 % doping had excellent optical transmittance (~85–90 %) in the 400–1100 nm wavelength range. The photoluminescence spectra of the AZO films revealed UV near band edge emission peaks in the 378–401 nm range and an oxygen-vacancy related peak around 471 nm. The addition of aluminium changed the band gap of zinc oxide from 3.29 to 3.41 eV, and the appearance of a new level was observed in the band gap at the higher aluminium doping concentrations. The AZO thin films showed good conductivity (in the order of 10−2 Ω cm) which allows their use as transparent electrodes. Moreover, the AZO thin films were stable in open air for 30 days.

A study on the Al doping behavior with sol aging time and its effect on structural and optical properties of sol–gel prepared ZnO thin films

A series of aluminum doped zinc oxide (AZO) thin films were prepared by sol–gel method on glass substrates to investigate the behavior of Al doping with sol aging time (as-prepared to 2weeks). X-ray diffraction analysis revealed a considerable shift in (002) diffraction peak towards higher diffraction angles with increasing sol aging time from as-prepared to 24h which was found to be reverse with further aging. X-ray photoelectron spectroscopy and UV–vis spectroscopy were performed to investigate the change in chemical states of Al/Zn/O atoms and band gap fluctuations respectively. It was found that more Al atoms were doped into ZnO lattice with the increment of sol aging time and saturated level was achieved for ~20–24h. Field emission scanning electron microscope and atomic force microscope characterization showed dense and homogeneous film morphology with decreasing relative surface roughness with sol aging time. Photoluminescence analysis and UV–vis spectroscopy revealed defect free films by exhibiting high optical transmission in the visible regime and found to improve with sol aging time. It could be concluded that solution aging time clearly influence the doping behavior and a suitable aging provides more stability which results into more Al atoms substitution for Zn in ZnO crystal lattice that affect the structural, morphological and optical properties of AZO thin films.

Effects of Oxygen Flux on the Aluminum Doped Zinc Oxide Thin Films By Direct Current Magnetron Sputtering

Abstract Aluminum doped zinc oxide (AZO) thin films were prepared by direct current (DC) magnetron sputtering with pure argon gas on glass substrates, usually showed relatively low transmission in our experiments. It was unfavorable for AZO as front electrode for silicon thin film solar cells. In order to increase the transmission of AZO thin films, we tried to add oxygen gas into vacuum chamber during sputtering processes. The microstructures, optical and electrical properties of AZO films were investigated. During the process of sputtering, the O2 flow rate indicated a greater negative impact on the electrical properties of AZO thin films than the improvement of optical properties. Raman peak related to zinc interstitial atoms (560cm-1) was observed in the AZO thin films grown with different O2 flow rates. With the increasing of O2 flow rate, intensity of Raman peak at 560cm-1 decreased. When the O2 flow rate increased, more O atoms involved in the process of reactive sputtering, and O and Zn interstitial atoms combined to Zn-O bond, which reduced the Zn interstitial atoms. The transmission between 400 nm and 1100 nm was enhanced by the increase of O2 flow rate. The average transmissions of AZO thin films were more than 90% in the visible and near-infrared range and the resistivity of these films increased acutely.

Influence of various thickness metallic interlayers on opto-electric and mechanical properties of AZO thin films on PET substrates

Various thickness metallic interlayers to improve the opto-electric and mechanical properties of aluminum-doped zinc oxide (AZO) thin films deposited on flexible polyethylene terephtalate (PET) substrates are studied. The effects of the interlayers on the resistance and transmittance of the AZO thin films are discussed. The result shows that the metallic interlayers effectively improve the electric resistance but reduce the optical transmittance of the AZO thin films. These phenomena become more obvious as the interlayer thickness increases. However, the AZO with an aluminum interlayer still behaves an acceptable transmittance. Moreover, mechanical tests indicate that the aluminum interlayer increases the hardness and modulus, and reduce the residual stress of the AZO thin films. In contrast, the silver and copper interlayers decrease the AZO's mechanical properties. Comparing to those without any interlayer, the results show that the best interlayer is the 6nm thick aluminum film.

AZO Anode 전극을 적용한 OLED 소자의 제작과 전기적.광학적 특성 분석

AZO(Aluminum-doped Zinc Oxide) films are attractive materials as transparent conductive electrode because they are inexpensive, nontoxic and abundant element compared with ITO(Indium Tin Oxide). AZO films have been deposited on glass (corning 1737) substrates by RF magnetron sputtering. The AZO film was post-annealed at <TEX>$600^{\circ}C$</TEX> for 2 hr with <TEX>$N_2$</TEX> atmosphere. The AZO films were used as an anode contact to fabricate OLEDs(Organic Light Emitting Diodes). OLEDs with <TEX>$AZO/TPD/Alq_3/Al$</TEX> configuration were fabricated by thermal evaporation. We investigated that the electric, structural and optical properties of AZO thin films, which measured using the methods of XRD, SEM, Hall measurement and Spectrophotometer. The current density-voltage and luminescence-voltage properties of devices were studied and compared with ITO devices fabricated under the same conditions.