ZAO Films Research Articles

Dependence of Film Thickness on Properties of Al Doped ZnO Thin Films

In this study high quality of Al doped ZnO (ZAO) thin films were prepared by RF magnetron sputtering on glass substrates at room temperature in order to study the thickness effect upon their structure, electrical and optical properties. XRD results show that the films are polycrystalline and with strongly preferred (002) orientation perpendicular to substrate surface whatever the thickness is. The crystallite size was calculated by Williamson-Hall method, while it increases as the film thickness increased. The lattice stress is mainly caused by the growth process. Hall measurements revealed electrical parameter very dependent upon thickness when the thickness of ZAO film is lower than 700 nm. The resistivity decreased and the carrier concentration and Hall mobility increases as the film thickness increased. When film thickness becomes larger, only a little change in the above properties was observed. All the films have high transmittance above 90% in visible range. Red shift of the absorption edge was observed as thickness increased. The optical energy bandgap decreased from 3.41eV to 3.30 eV with the increase of film thickness.

Low-cost ZnO:Al transparent contact by reactive rotatable magnetron sputtering for Cu(In,Ga)Se 2 solar modules

Sputtering ZnO as transparent front contact (TCO) is standard in today's industrial scale Cu(In,Ga)Se 2 (CIGS) module manufacturing. Although innovative concepts like rotatable magnetron sputtering from ceramic targets have been realised, costs are still high due to expensive ceramic targets. Significant cost reductions are expected by using reactive sputtering of metallic targets. Therefore, ZSW and industrial partners investigated the reactive sputtering of Al-doped zinc oxide (ZAO) as TCO on CIGS absorbers of high quality and industrial relevance. The reactive DC sputtering from rotatable magnetron targets is controlled in the transition mode by adjusting oxygen flow and discharge voltage. Optimisation leads to ZAO films with a TCO quality nearly comparable to standard films deposited by DC ceramic sputtering. Scanning electron microscopy, X-ray diffraction, and Hall analyses of the ZAO films are performed. Medium-size CIGS modules are coated with reactively sputtered ZAO, resulting in 12.8% module efficiency and surpassing the efficiency of the ceramic witness device. Cd-free buffered devices are also successfully coated with reactive TCO. Damp heat stability according to IEC61646 is met by all reactively sputtered devices.

Study on XRDK Optical and Electrical performance of Transparent Conducting ZnO:Al(ZAO) Thin Films

The ZAO (ZnO: Al) thin films were prepared by DC reactive magnetron sputtering technique. The XRD electrical and optical properties of films are particular investigated. The results show that ZAO films are polycrystalline hexagonal wurtzite structure, and we are not find Al2O3 crystal phase. At the same time, we gained the high quality ZAO films with the minimum resistivuty of 4.5×10-4 Ω · cm, the transmittance in visible region above 80% and the reflectivity in IR region above 70%.

Preparation and character of textured ZnO:Al thin films deposited on flexible substrates by RF magnetron sputtering

ZnO:Al thin films deposited on transparent TPT substrates by magnetron sputtering were etched in acetic acid solution. The effects of etching solution concentration and etching time on the structure and properties of ZnO:Al films were investigated. The obtained films had a hexagonal structure and a highly preferred orientation with the c-axis perpendicular to the substrate. The ZAO film etched in 1% acetic acid solution for 10 s had a pyramidal structure and an enhanced light scattering ability, the average transmittance and reflectance in the visible region were 72% and 26% respectively, the sheet resistance was 260 Ω/□. Both transmittance and reflectance of the films decreased as the etching solution concentration and etching time increasing. Etching had a negative effect on the conductive properties of ZAO films. The lowest sheet resistance was 120 Ω/□ for the ZAO film without etching.

Analysis on the process of ZAO films by DC magnetron reactive sputtering

The ZAO (ZnO:Al) thin films were prepared by DC reactive magnetron sputtering technique. The relationship between the process parameters and the organizational structure, optical and electrical properties was studied. Through optimizing the process parameters, an optimal preparation parameter can be obtained. Using the optimal parameters to prepare the ZAO thin films, the resistivity of the ZAO film is as low as 4.5×10−4 Ω·cm and the average transmissivity in the visible region is around 80%, the optical and electrical properties meet the application requirements.

Orthogonal optimization for room temperature magnetron sputtering of ZnO:Al films for all-solid electrochromic devices

In order to obtain competent and quality (high transparency, conductivity and stability) aluminium-doped zinc oxide (ZnO:Al, ZAO) films for all solid electrochromic devices, ZAO films were prepared by direct current (D.C.) reactive magnetron sputtering at room temperature based on orthogonal design. Optical and electrical property dependences of the films on the four dominant sputtering parameters: sputtering time, target–substrate distance, sputtering power and O2 flow ratio were simultaneously investigated with measured results using mathematical and statistical method. Optimal Parameters to fabricate ZAO films with optimum comprehensive performances were obtained ultimately. Resistivity and carrier concentration of ZAO film deposited with optimized parameters were 3.89×10−4Ωcm and 1.09×1021cm−3, respectively. ZAO films with these superior properties were employed as transparent electrodes eventually in a WO3 based all-solid electrochromic device which displayed good electrochromic performance. The regulation range for transmittance in the visible region of the device was more than 50%, which was comparable to that of the device adopting indium tin oxide (ITO) films as electrodes.

Effects of Power on Properties of ZnO:Al Films Deposited on Flexible Substrates by RF Magnetron Sputtering

Aluminium doped ZnO thin films(ZnO:Al) films were deposited on transparent TPT substrate at room temperature by RF magnetron sputtering. The effects of sputtering power on structural, optical and electrical properties were investigated by X-ray diffractometery (XRD), scanning electron microscope (SEM), UV-visible spectrophotometer, as well as Hall Effect Measurement System. Results revealed that the obtained film had a hexagonal structure and a highly (0 0 2) preferred orientation with the c-axis perpendicular to the substrate. The grain size and preferred orientation of crystallites showed dependence on the sputtering power. The optical transmittance of the ZAO films depended strongly on the sputtering power and decreased with increasing power.The transmittance of the ZAO film at 80W was over 80% in the visible region. And the electrical properties of the ZAO films are improved with the increase of the sputtering power.The resistivity of obtained film at 200W was 3.15×10-2Ω•cm.

Effects of atomic oxygen treatment on structures, morphologies and electrical properties of ZnO:Al films

ZnO:Al (ZAO) film has a potential application in providing spacecrafts the protection against atomic oxygen (AO) erosion. To advance the understanding of the AO resisting mechanisms and the relationships between the structures, morphologies and conductive properties of ZAO film, direct current magnetron sputtered ZAO films with different thicknesses were treated with AO in a ground-based simulation facility. The microstructure, surface chemical state, morphologies and electrical properties of pristine films and irradiated ones were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and Hall measurement. It is found that AO exposure produces novel, oriented recrystallization of the surface particles. It also increases the content of oxygen ions in fully oxidized stoichiometric surroundings on the surface, resulting in the decrease of the conductivity. As the thickness of ZAO film increases, the crystallinity, conductivity and resistance to AO erosion are all improved.

Influence of the gas flow of Argon and the distance between substrate and plasma on properties of Al-doped zinc oxide films

Al-doped ZnO(ZAO) films were deposited by DC magnetron sputtering using facing zinc oxide targets at room temperature and in argon atmosphere. The effects of the gas flow of Argon and the distance between substrate and plasma on the properties of the ZAO thin films were characterized by several techniques. By optimizing the craft of preparation, the electrical resistivity as low as 3.3×10-4 Ω·cm and the optical transmittance over 80% in the visible range were obtained for these thin ZAO films. Therefore, the ZAO thin films were suitable for the window layers of n-i-p thin film solar cells or transparent conductive films.

Preparation of Mg and Al co-doped ZnO thin films with tunable band gap

Al （Al2O3，2wt%） doped ZnO thin films （ZAO） with tunable band gap，alloyed with different Mg contents （1wt%，3wt% and 5wt%），were prepared by radio frequency magnetron sputtering on glass substrates and annealed at 500℃ in air. The optical and electrical properties of the films were measured by X-ray diffractometer，four-point probe method，Hall-effect configuration，and UV-VIS spectrophotometer. The results show that the Mg co-doped ZAO thin films have a wurtzite structure with （002） preferred orientation. Compared with ZAO film，the optical transmission of Mg co-doped ZAO thin films in the ultraviolet region increases and the average optical transmissions in the visible region is greater than 85%，except the 5wt% Mg doped films. The band gaps of ZAO and Mg co-doped ZAO thin films can be modulated from 344 eV to 351 eV by increasing the Mg content from 1wt% to 5wt%. For 1wt%，3wt% and 5wt% Mg doping，the Mg co-doped ZAO thin films have the resistivity of 12×10-3，37×10-3 and 85×10-3 Ω·cm，respectively. Stokes shifts of 20，14 and 50 meV were observed for doping of 1wt%，3wt%，and 5wt% Mg contents. We find that a large Mg doping content will degrade the crystal quality of Mg co-doped ZAO thin films，decrease the optical transmissions in the visible region and decrease the carrier mobility in the films. Therefore，the resistivity of Mg co-doped ZAO thin films increases with the Mg doping content.

Investigation of correlation between the microstructure and electrical properties of sol-gel derived ZnO based thin films

Pure ZnO and aluminum doped ZnO films (ZAO) were prepared by sol-gel method and the effect of Al doping on the microstructure and electrical properties of the films was investigated. The results showed that the transformation from granular to columnar structure could be observed in pure ZnO films with the increase in heating time while in aluminum doped films little structural changes occurred even after a prolonged heating time. Additionally, measurements of electrical properties showed that both microstructural evolution and doping could significantly improve the conductivity of the films, which could be assigned to an increase both in Hall mobility and carrier concentration. The relationship between microstructure and the electrical properties of the films was discussed, and various scattering mechanisms were proposed for sol-gel derived ZnO and ZAO films as a function of the carrier concentration.

Structural, electrical and optical properties of Al–Ti codoped ZnO (ZATO) thin films prepared by RF magnetron sputtering

Al–Ti codoped ZnO (ZATO) thin films were grown on glass substrates at room temperature by radio frequency (RF) magnetron sputtering technique and annealed under vacuum (∼10 −1 Pa) at 400 °C for 3 h. The X-ray diffraction (XRD) patterns show that Al-doped ZnO (ZAO) and ZATO thin films are highly textured along the c-axis and perpendicular to the surface of the substrate. After annealing in a vacuum condition at 400 °C for 3 h, the lowest resistivity of 7.96 and 8.7 × 10 −4 Ω cm are observed for ZATO and ZAO films, respectively. But after annealing in air, the resistivity of ZATO and ZAO is higher than 10 5 Ω cm. In the visible region, the ZAO films show the average transmittance of the order of 90%, while ZATO films were of the order of 75%, which illustrates that the additional Ti doping reduces the optical properties. The optical band gap was found to be 3.46 eV for ZAO film and it increases to 3.53 eV for ZATO films.

Effects of Atomic Oxygen Irradiation on Transparent Conductive Oxide Thin Films

Transparent conductive oxide (TCO) thin film is a kind of functional material which has potential applications in solar cells and atomic oxygen (AO) resisting systems in spacecrafts. Of TCO, ZnO:Al (ZAO) and In2O3:Sn (ITO) thin films have been widely used and investigated. In this study, ZAO and ITO thin films were irradiated by AO with different amounts of fluence. The as-deposited samples and irradiated ones were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Hall-effect measurement to investigate the dependence of the structure, morphology and electrical properties of ZAO or ITO on the amount of fluence of AO irradiation. It is noticed that AO has erosion effects on the surface of ZAO without evident influences upon its structure and conductive properties. Moreover, as the amount of AO fluence rises, the carrier concentration of ITO decreases causing the resistivity to increase by at most 21.7%.

Role of oxygen desorption during vacuum annealing in the improvement of electrical properties of aluminum doped zinc oxide films synthesized by sol gel method

Aluminum doped zinc oxide (ZAO) films were prepared by sol gel dip-coating process. Several annealing treatments were carried out to improve the conductivity of ZAO films. The results show that the annealing temperature and the cooling rate have significant effects on the resistivity of ZAO films. A minimum resistivity of 5.97×10−3Ωcm with the transmission in visible light region above 85% can be obtained after vacuum annealing. The desorption of oxygen that is chemisorbed on the surface and at the grain boundary is thought to be responsible for the observed improvement.

Highly efficient p-i-n-type organic light emitting diodes on ZnO:Al substrates

Aluminum doped zinc oxide (ZAO) is presented in this letter as an alternative transparent electrode: optimized ZAO films offer excellent parameters for organic light emitting diodes (OLEDs). The ZAO films are applied to various p-i-n-type OLEDs. By using green phosphorescent molecules in a double emitter structure, very high efficiencies were obtained, namely, 54.6cd∕A and 61.5lm∕W for 100cd∕m2 at 2.78V. Additionally, white OLEDs on ZAO demonstrated pure white emission independent of the luminance and high efficiencies of 12.6cd∕A and 14.5lm∕W for 100cd∕m2 at 2.6V, which is comparable to indium-tin-oxide based white OLEDs.

Structural, electrical and optical properties of Gd doped and undoped ZnO:Al (ZAO) thin films prepared by RF magnetron sputtering

The influence of the gadolinium doping on the structural features and opto-electrical properties of ZnO:Al (ZAO) films deposited by radio frequency (RF) magnetron sputtering method onto glass substrates was investigated. X-ray analysis showed that the films were polycrystalline fitting well with a hexagonal wurtzite structure and have preferred orientation in [0 0 2] direction. The Gd doped ZAO film with a thickness of 140 nm showed a high visible region transmittance of 90%. The optical band gap was found to be 3.38 eV for pure ZnO film and 3.58 eV for ZAO films while a drop in optical band gap of ZAO film was observed by Gd doping. The lowest resistivities of 8.4 × 10 −3 and 10.6 × 10 −3 Ω cm were observed for Gd doped and undoped ZAO films, respectively, which were deposited at room temperature and annealed at 150 °C.

Shave‐off depth profiling of transparent conductive films and data analysis of the profile

AbstractAluminum doped zinc oxide (ZAO) is a promising material for transparent conductive films, but higher conductivity is needed for its use in flat‐panel displays. Its conductivity depends on the deposition conditions, and the segregation of aluminum is suspected as one of causes for its low conductivity. But it has not been confirmed yet because of the low aluminum content in ZAO films.‘Shave‐off depth profiling’ is one of the methods that can be used to analyze such samples. By applying this method, multiple elements can be detected simultaneously and with high sensitivity. Furthermore, even samples with surface roughness can be analyzed accurately.We have acquired the shave‐off depth profile of a ZAO thin film and attempted to obtain depth information. However, when the film thickness is insufficient, it is difficult to obtain the depth information directly from the profile. To solve this problem, we now propose a new data analysis method for the shave‐off depth profile, and apply the method to the depth profiling of the ZAO thin film. Copyright © 2006 John Wiley & Sons, Ltd.

Characteristics of Al doped zinc oxide (ZAO) thin films deposited by RF magnetron sputtering

ZAO and ITO thin films were prepared by RF magnetron sputtering. In this study, three of the sputtering parameters, that is, substrate temperature, oxygen flow rate and RF discharge power were varied separately to fabricate samples. The range of variation of substrate temperature was from room temperature to 623K. The relative concentration of O2 in the ambient gas in the chamber was 0% or 25%. The sputtering rate was changed by controlling the discharge power. The minimum surface resistivity of ZAO was 2.53×102Ω/cm2 for samples sputtered at a substrate temperature of 373K and that of ITO was 2.37×101Ω/cm2 sputtered under standard conditions. Visible light transmittances of these samples were 89.9% and 90.2%, respectively. From these results, it is suggested that when sputtered with optimum sputtering parameters, ZAO is a potential material for practical use for transparent conducting electrodes (TCO) for PDPs.

Enhanced Cathodoluminescent Properties of Nanoencapsulated Zinc Sulfide Phosphors

In this paper we show that nanoencapsulated oxygen deficient aluminum doped zinc oxide (ZAO) coatings can significantly reduce the electron beam degradation of sulfide-based phosphors. The nanoencapsulated coatings on particles were synthesized using a modified pulsed laser ablation deposition technique. Microstructural studies indicate that an oxygen deficient ZAO film acts as both a diffusion barrier and an oxygen getter during the electron beam irradiation process. Under optimized deposition conditions, the degradation lifetime of nanoencapsulated zinc sulfide phosphors increased by more than an order of magnitude, compared to noncoated material.

Properties of transparent conducting ZnO : Al oxide thin films and their application for molecular organic light-emitting diodes

ZnO:AI (ZAO) films were deposited on glass substrates by a reactive mid-frequency sputtering system. The microstructural, electrical, and optical properties of ZAO films were investigated. It was observed that the polycrystalline film was (0 0 2 n)textured with columnar structure. The minimum resistivity was 1.39 x 10(-4) Omegacm with a carrier concentration of 1.58 x 10(21) cm(-3) and a Hall mobility of 28.2 cm(2) V-1 s(-1), correspondingly with the c-axis nearly equal to the value of ZnO powder and the minimum mechanical stress therein. The average transmittance of 80.8% in the visible range and infrared reflectance of over 86% in the 1600-4400 cm(-1) interval were obtained. The ZAO films were used as the transparent anodes to fabricate light-emitting diodes, and a luminance efficiency of 2.09 cd A(-1) was measured at a current density of 5.38 A m(-2). (C) 2004 Kluwer Academic Publishers.