Aluminum-doped zinc oxide films grown by atomic layer deposition for transparent electrode applications

We obtained zinc oxide films doped with aluminum using atomic layer deposition (ALD). Their morphology, growth mode, optical and electrical properties are studied. Al content dependence is analyzed. Carrier scattering mechanisms in ZnO:Al (AZO) films are investigated from conductivity versus temperature measurements. We also discuss how the film thickness affects its resistivity and optical transmission. The obtained film resistivities, i.e. 7 × 10^?4 ??cm, belong to the lowest reported so far for transparent ZnO:Al films grown by the ALD method.     

Transparent conducting ZnO : Al films on different organic substrates deposited by r.f. sputtering

1. IntroductionThansparellt conducting zinc oxide films have beenextensively studied in recede years, because of theirlow material cost, relatively low deposition temperature and stability in hydrogen plasma compared withITO and SnOZ films[1]. These adVatages are of considerable interest for electrrvoptical conversion device.Compared with undoped ZnO, Al-doped ZnO filmshave lobed resistivity and better stability. nansparellt conducting films deposited on organic substrateshave many lments…     

Characteristics of ZnO films prepared by atomic layer deposition for transparent electronic devices

Recently, nanostructured zinc oxide (ZnO) for many different applications in micro- and opto-electronic devices has been studied intensively. However, its structural and electrical properties still require improvements for ZnO-based transparent electronics. In this study, we fabricated ZnO films (thicknesses from 30 to 70 nm) on glass substrates using atomic layer deposition (ALD) and investigated the film properties in relation with substrate temperatures. The processing window (thermal ALD window) of self-limiting growth was observed at 110-190 degrees C. In our thermal ALD window, the average growth rate of ZnO films was 0.26 nm/cycle, and the (002) orientation became dominant with increasing substrate temperatures. For all growth temperatures, ZnO films have shown n-type conductivity. At 170 degrees C, ZnO with good electrical properties of carrier concentration (1.3 x 10(19) cm(-3)), mobility (18 cm2/Vs), and resistivity (2.7 x 10(-2) omegacm) was successfully obtained.     

Atomic layer deposition of Zn1−x Mg x O:Al transparent conducting films

Aluminum-doped zinc magnesium oxide (Zn_1?x Mg _x O:Al) films with the Mg content from x = 0 to 0.48 were obtained using atomic layer deposition (ALD). Together with the thorough studies of the properties of the deposited films, the ALD growth parameters conditioning possible applications of Zn_1?x Mg _x O:Al films as transparent electrodes are investigated. Very low film resistivities (≤~10^?3 Ω cm) and the metallic-type conductivity behavior at room temperature for Zn_1?x Mg _x O:Al films are observed for Mg content x < 0.19. The Mg content of x = 0.19 results in the optical absorption edge of Zn_1?x Mg _x O:Al films at 3.81 eV (325 nm). Other film parameters like work function or sheet resistance can be easily modified by variation of growth parameters.     

Preparation of ZnO:Al thin film on transparent TPT substrate at room temperature by RF magnetron sputtering technique

Aluminum doped ZnO thin films (ZnO:Al) deposited on flexible substrates are suitable to be used as transparent conductive oxide (TCO) thin films in solar cells because of the excellent optical and electrical properties. TPT films are a kind of composite materials and are usually used as encapsulation material of solar panels. In this paper, ZnO:Al film was firstly deposited on transparent TPT substrate by RF magnetron sputtering. The structural, optical, and electrical properties of the film were investigated by X-ray diffractometry (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 preferred orientation with the c-axis perpendicular to the substrate. Also, the film showed a high optical transmittance over 80% in the visible region and a resistivity of about 3.03 × 10^? 1 Ω·cm.     

Indium-doped ZnO thin films deposited by the sol–gel technique

Conducting and transparent indium-doped ZnO thin films were deposited on sodocalcic glass substrates by the sol–gel technique. Zinc acetate and indium chloride were used as precursor materials. The electrical resistivity, structure, morphology and optical transmittance of the films were analyzed as a function of the film thickness and the post-deposition annealing treatments in vacuum, oxygen or argon. The obtained films exhibited a (002) preferential growth in all the cases. Surface morphology studies showed that an increase in the films' thickness causes an increase in the grain size. Films with 0.18 μm thickness, prepared under optimal deposition conditions followed by an annealing treatment in vacuum showed electrical resistivity of 1.3 × 10^− 2 Ωcm and optical transmittance higher than 85%. These results make ZnO:In thin films an attractive material for transparent electrodes in thin film solar cells.     

ZnO thin films prepared by atomic layer deposition and rf sputtering as an active layer for thin film transistor

Recently, the application of ZnO thin films as an active channel layer of transparent thin film transistor (TFT) has become of great interest. In this study, we deposited ZnO thin films by atomic layer deposition (ALD) from diethyl Zn (DEZ) as a metal precursor and water as a reactant at growth temperatures between 100 and 250 °C. At typical growth conditions, pure ZnO thin films were obtained without any detectable carbon contamination. For comparison of key film properties including microstructure and chemical and electrical properties, ZnO films were also prepared by rf sputtering at room temperature. The microstructure analyses by X-ray diffraction have shown that both of the ALD and sputtered ZnO thin films have (002) preferred orientation. At low growth temperature T_s ≤ 125 °C, ALD ZnO films have high resistivity (> 10 Ω cm) with small mobility (< 3 cm²/V s), while the ones prepared at higher temperature have lower resistivity (< 0.02 Ω cm) with higher mobility (> 15 cm²/V s). Meanwhile, sputtered ZnO films have much higher resistivity than ALD ZnO at most of the growth conditions studied. Based upon the experimental results, the electrical properties of ZnO thin films depending on the growth conditions for application as an active channel layer of TFT were discussed focusing on the comparisons between ALD and sputtering.     

Control of ZnO thin film surface by ZnS passivation to enhance photoluminescence

To enhance the optical property of zinc oxide (ZnO) thin film, zinc sulfide (ZnS) thin films were formed on the interfaces of ZnO thin film as a passivation and a substrate layer. ZnO and ZnS thin films were deposited by atomic layer deposition (ALD) using diethyl zinc, H₂O, and H₂S as precursors. Investigations by X-ray diffraction and transmission electron microscopy showed that ZnS/ZnO/ZnS multi-layer thin films with clear boundaries were achieved by ALD and that each film layer had its own polycrystalline phase. The intensity of the photoluminescence of the ZnO thin film was enhanced as the thickness of the ZnO thin film increased and as ZnS passivation was applied onto the ZnO thin film interfaces.     

室温下射频磁控溅射制备ZnO:Al透明导电薄膜及其性能研究

采用射频磁控溅射技术,在室温下,以ZnO:Al2O3(2%Al2O3(质量比))为靶材,在石英玻璃基底上,采用不同工艺条件制备了ZnO:Al(AZO)薄膜。使用扫描电子显微镜观察了薄膜的表面形貌,X射线衍射分析了薄膜的结构,四探针测量仪得到薄膜的表面电阻,轮廓仪测量了薄膜厚度,并计算了电阻率,最后采用分光光度计测量了薄膜的透过率;研究了溅射功率、溅射气压与薄膜厚度对薄膜电阻率及透过率的影响。结果表明:所制备的AZO薄膜具有(002)择优取向,并且发现薄膜厚度对薄膜的光电性能有明显影响,溅射气压和溅射功率对薄膜电学性能有较大影响,但是对薄膜透过率影响不大。当功率为1kW、溅射气压0.052Pa、AZO薄膜厚度为250nm时,其电阻率为8.38×10-4Ω·cm,波长在550nm处透过率为89%,接近基底的本底透过率92%。当薄膜厚度为1125 nm时薄膜的电阻率降至最低(6.16×10-4Ω·cm)。     

Atomic layer deposition ultra-barriers for electronic applications-strategies and implementation

We show that Al2O3 thin films, grown by atomic layer deposition (ALD) on polyester, are ultrabarriers with moisture permeation <10(-5) g-H2O/m2-day, as determined after aging for more than three years. We present evidence that the mechanism for gas permeation in ALD Al2O3 films is not due to pinholes, but that the onset of permeation occurs abruptly, analogous to electrical breakdown in oxide thin films. We show that the permeation onset time increases for thicker Al2O3 films and higher ALD process temperature, for which the hydrogen defect concentration in Al2O3 films is less. Further, we show that mild plasma treatment of the polyester, prior to ALD deposition of Al2O3, makes the surface more hydrophilic and reduces moisture permeation compared to an untreated surface. Similarly, ALD deposition on the bare or non-slip side of the polyester film is preferred for low permeation.     

Characterization of ZnO：Al Films Deposited on Organic Substrate by r.f. Magnetron Sputtering

Transparent conducting Al-doped zinc oxide (ZnO:AI) films with good adhesion have been deposited on polyimide thin film substrates by r.f. magnetron sputtering technique at low substrate temperature (25-180℃). The structural, optical and electrical properties of the deposited films were investigated. High quality films with electrical resistivity as low as 8.5×10-4 Ω·cm and the average transmittance over 74% in the wavelength range of the visible spectrum have been obtained. The electron carrier concentrations are in the range from 2.9×1020 to 7.1×1020 cm-3 with mobilities from 4 to 8.8 cm2 V-1s-1. The densities of the films are in the range from 4.58 to 5.16 g/cm-3.     

Plasma emission monitoring (PEM) controlled DC reactive sputtered ZnO:Al thin films

High deposition rate ZnO:Al films have been produced at room temperature by reactive DC sputtering using a plasma emission monitoring (PEM) control system. We have investigated the relationship between structural, optical and electrical properties of the ZnO:Al films. Crystal structures of the films have been studied by X-ray diffraction. Optimum ZnO:Al films, with 17-40 Ω/□ sheet resistance range and transmittance approaching 88% in the visible region, exhibited a hexagonal ZnO structure with preferential (002) orientation and crystallite sizes of about 27 nm. Resistive transparent films displayed a more random orientation showing peaks at (100) and (102) orientations. Dark “metallic” films were shown to consist of mainly zinc. The optimal ZnO:Al film has been determined from a figure of merit based on power losses due to absorption and series resistance in the ZnO:Al films. It is highly transparent, with low resistance, pronounced (002) peak and large crystallite size.     

Laser damage properties of TiO2/Al2O3 thin films grown by atomic layer deposition

Research on thin film deposited by atomic layer deposition (ALD) for laser damage resistance is rare. In this paper, it has been used to deposit TiO(2)/Al(2)O(3) films at 110 °C and 280 °C on fused silica and BK7 substrates. Microstructure of the thin films was investigated by x-ray diffraction. The laser-induced damage threshold (LIDT) of samples was measured by a damage test system. Damage morphology was studied under a Nomarski differential interference contrast microscope and further checked under an atomic force microscope. Multilayers deposited at different temperatures were compared. The results show that the films deposited by ALD had better uniformity and transmission; in this paper, the uniformity is better than 99% over 100 mm Φ samples, and the transmission is more than 99.8% at 1064 nm. Deposition temperature affects the deposition rate and the thin film microstructure and further influences the LIDT of the thin films. As to the TiO(2)/Al(2)O(3) films, the LIDTs were 6.73±0.47 J/cm(2) and 6.5±0.46 J/cm(2) at 110 °C on fused silica and BK7 substrates, respectively. The LIDTs at 11 °C are notably better than 280 °C.     

The effects of using ALD-grown ZnO buffer layers on the properties of indium tin oxide grown by chemical solution deposition

In comparison to ITO films prepared by chemical solution deposition on bare substrates, the use of a ZnO buffer layer and Al2O3 barrier layer has been shown to have a significant effect on morphology, measured sheet resistance and therefore resistivity. In the case of quartz substrates, ITO resistivity decreased from 9.6 x 10(-3) ohms cm to 4.3 x 10(-3) ohms cm on incorporation of a ZnO buffer layer and Al2O3 barrier layer, both grown by ALD. A change in surface morphology was observed, due to the presence of the buffer layer, however, the ZnO buffer layer was not found to influence the XRD pattern of the ITO films.     

Filtered vacuum arc deposition of transparent conducting Al-doped ZnO films

Transparent conducting ZnO:Al and ZnO films of 380-800 nm thickness were deposited on glass substrates by filtered vacuum arc deposition (FVAD), using a cylindrical Zn cathode doped with 5-6 at.% Al or a pure Zn cathode in oxygen background gas with pressure P = 0.4-0.93 Pa. The crystalline structure, composition and electrical and optical properties of the films were studied as functions of P. The films were stored under ambient air conditions and the variation of their resistance as function of storage time was monitored over a period of several months.The Al concentration in the film was found to be 0.006-0.008 at.%, i.e., a few orders of magnitude lower than that in the cathode material. However, this low Al content influenced the film resistivity, ρ, and its stability. The resistivity of as-deposited ZnO:Al films, ρ = (6-8) × 10^− 3 Ω cm, was independent of P and lower by a factor of 2 in comparison to that of the ZnO films deposited by the same FVAD system. The ρ of ZnO films 60 days after deposition increased by a factor of ∼ 7 with respect to as-deposited films. The ZnO:Al films deposited with P = 0.47-0.6 Pa were more stable, their ρ first slowly increased during the storage time (1.1-1.4 times with respect to as-deposited films), and then stabilized after 30-45 days.     

Deposition of Al doped ZnO layers with various electrical types by atomic layer deposition

AlZnO thin films with various Al/Zn composition ratios were deposited by atomic layer deposition (ALD) at 200 °C. The effect of the composition of the AlZnO films on their electrical and optical characteristics was investigated. The AlZnO films with an Al content of up to 10 at.% showed high conductivity, while further increasing in the Al content resulted in the abrupt formation of an insulating oxide film. The lowest electrical resistivity of the ALD-deposited AlZnO film was 6.5 × 10^− 4 [Ω cm] at 5 at.% Al. The AlZnO films with up to 5 at.% Al exhibited crystalline phases and a near-band-edge emission. With increasing Al content, the optical band edge showed a blue shift, and a sudden shift associated with an insulating bandgap was observed in the AlZnO films containing 20 at.% Al.     

湿法刻蚀对ZnO∶Al透明导电薄膜结构与性能的影响

室温下通过直流磁控溅射Al2O3掺杂3％(质量分数)的ZnO靶材制备了厚度约1μm、结晶度高、表面平整光滑的ZnO∶Al透明导电薄膜.研究盐酸、王水和草酸溶液对ZnO∶Al薄膜的湿化学刻蚀行为,分析刻蚀对薄膜微观结构、光刻图案、电学和光学性能的影响.结果表明,刻蚀对薄膜的结晶取向性无影响;经盐酸、王水和草酸刻蚀后薄膜的电阻率略有增大,从7.4mΩ·cm分别增大到8.7mnΩ· cm、8.8mQ·cm和8.6mΩ·cm;透光率略有下降,从80％分别下降到76％、77％和78％.0.5％的盐酸刻蚀可以获得结构良好的陷光结构.薄膜在盐酸中刻蚀速率快,易产生浮胶;在草酸中刻蚀图案清晰,但存在残留;在王水中刻蚀图案清晰且无残留.     

Natively textured surface aluminum-doped zinc oxide transparent conductive layers for thin film solar cells via pulsed direct-current reactive magnetron sputtering

Natively textured surface aluminum-doped zinc oxide (ZnO:Al) layers for thin film solar cells were directly deposited without any surface treatments via pulsed direct-current reactive magnetron sputtering on glass substrates. Such an in-situ texturing method for sputtered ZnO:Al thin films has the advantages of efficiently reducing production costs and dramatically saving time in photovoltaic industrial processing. High purity metallic Zn-Al (purity: 99.999%, Al 2.0 wt.%) target and oxygen (purity: 99.999%) were used as source materials. During the reactive sputtering process, the oxygen gas flow rate was controlled using plasma emission monitoring. The performance of the textured surface ZnO:Al transparent conductive oxides (TCOs) thin films can be modified by changing the number of deposition rounds (i.e. thin-film thicknesses). The initially milky ZnO:Al TCO thin films deposited at a substrate temperature of ~ 553 K exhibit rough crater-like surface morphology with high transparencies (T ~ 80-85% in visible range) and excellent electrical properties (ρ ~ 3.4 × 10^− 4 Ω cm). Finally, the textured-surface ZnO:Al TCO thin films were preliminarily applied in pin-type silicon thin film solar cells.     

Al2O3 and TiO2 atomic layer deposition on copper for water corrosion resistance

Al(2)O(3) and TiO(2) atomic layer deposition (ALD) were employed to develop an ultrathin barrier film on copper to prevent water corrosion. The strategy was to utilize Al(2)O(3) ALD as a pinhole-free barrier and to protect the Al(2)O(3) ALD using TiO(2) ALD. An initial set of experiments was performed at 177 °C to establish that Al(2)O(3) ALD could nucleate on copper and produce a high-quality Al(2)O(3) film. In situ quartz crystal microbalance (QCM) measurements verified that Al(2)O(3) ALD nucleated and grew efficiently on copper-plated quartz crystals at 177 °C using trimethylaluminum (TMA) and water as the reactants. An electroplating technique also established that the Al(2)O(3) ALD films had a low defect density. A second set of experiments was performed for ALD at 120 °C to study the ability of ALD films to prevent copper corrosion. These experiments revealed that an Al(2)O(3) ALD film alone was insufficient to prevent copper corrosion because of the dissolution of the Al(2)O(3) film in water. Subsequently, TiO(2) ALD was explored on copper at 120 °C using TiCl(4) and water as the reactants. The resulting TiO(2) films also did not prevent the water corrosion of copper. Fortunately, Al(2)O(3) films with a TiO(2) capping layer were much more resilient to dissolution in water and prevented the water corrosion of copper. Optical microscopy images revealed that TiO(2) capping layers as thin as 200 ? on Al(2)O(3) adhesion layers could prevent copper corrosion in water at 90 °C for ~80 days. In contrast, the copper corroded almost immediately in water at 90 °C for Al(2)O(3) and ZnO films by themselves on copper. Ellipsometer measurements revealed that Al(2)O(3) films with a thickness of ~200 ? and ZnO films with a thickness of ~250 ? dissolved in water at 90 °C in ~10 days. In contrast, the ellipsometer measurements confirmed that the TiO(2) capping layers with thicknesses of ~200 ? on the Al(2)O(3) adhesion layers protected the copper for ~80 days in water at 90 °C. The TiO(2) ALD coatings were also hydrophilic and facilitated H(2)O wetting to copper wire mesh substrates.     

采用水基原子层沉积工艺在石墨烯上沉积Al2O3介质薄膜研究

采用水基原子层沉积(H2O-based ALD)方法在石墨烯上直接生长Al2O3介质薄膜,研究了Al2O3成核机理.原子力显微镜(AFM)对Al2O3薄膜微观形态分析表明,沉积温度决定着Al2O3在石墨烯表面的成核生长情况,物理吸附在石墨烯表面的水分子是Al2O3成核的关键,物理吸附水分子的均匀性直接影响Al2O3薄膜的均匀性.在适当的温度窗口(100～130℃),Al2O3可以均匀沉积在石墨烯上,AFM测得Al2O3薄膜表面均方根粗糙度(RMS)为0.26 nm,X射线光电子能谱(XPS)表面分析与元素深度剖析表明,120℃下在石墨烯表面沉积的Al2O3薄膜中O和Al元素的含量比约为1.5.拉曼光谱分析表明,采用H2O-based ALD工艺沉积栅介质薄膜不会降低石墨烯晶体质量.