New natively textured surface Al-doped ZnO-TCOs for thin film solar cells via magnetron sputtering

Natively textured surface aluminum doped zinc oxide (ZnO:Al) thin films were directly deposited via pulsed direct current (DC) reactive magnetron sputtering on glass substrates. During the reactive sputtering process, the oxygen gas flow rate was varied from 8.5 sccm to 11.0 sccm. The influences of oxygen flow rate on the structural, electrical and optical properties of naturally textured ZnO:Al TCO thin films with milky surface were investigated in detail. Gradual oxygen growth (GOG) technique was developed in the reactive sputtering process for textured ZnO:Al thin films. The light-scattering ability and optical transmittance of the natively textured ZnO:Al TCO thin films can be improved through gradual oxygen growth method while maintaining a low sheet resistance. Typical natively textured ZnO:Al TCO thin film with crater-like surface exhibits low sheet resistance (R_s ～ 4 Ω), high transmittance (T_a > 85%) in visible optical region and high haze value (12.1%).     

Mechanical properties of Al2O3-doped (2 wt.%) ZnO films

We report a new method of evaluating the adhesion of Al₂O₃-doped (2 wt.%) ZnO (AZO) thin films. The AZO films were deposited by DC reactive magnetron sputtering on plastic film (PET: polyethyleneterephthalate) at various sputtering pressures, power, and reactive gas-flow ratios. The adhesion test of the films was carried out using the nanoindentation system. The fracture point as determined by the load-displacement curve occurred at the time of separation between the thin film and the substrate. The integration value of load and displacement to the fracture point is defined as the degree of adhesion (S_W). The AZO films showed that adhesion increase as sputtering power increases and sputtering pressure decreases.     

Low-cost ZnO:Al transparent contact by reactive rotatable magnetron sputtering for Cu(In,Ga)Se2 solar modules

Sputtering ZnO as transparent front contact (TCO) is standard in today's industrial scale Cu(In,Ga)Se₂ (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.     

Discharge power dependence of structural and electrical properties of Al-doped ZnO conducting film by magnetron sputtering (for PDP)

In order to investigate the possible application of ZnO films as a transparent conducting oxide (TCO) electrode for AC PDP, ZnO:Al films were prepared by DC magnetron sputtering method. The effects of discharge power and doping concentration on the structural and electrical properties of ZnO films were mainly studied experimentally. Five-inch PDP cells using either a ZnO:Al or indium tin oxide (ITO) electrode were also fabricated separately under the same manufacturing conditions. The luminous properties of both the PDP cells were measured and compared with each other.By doping the ZnO target with 2 wt% of Al₂O₃, the film deposited at a discharge power of 40 W resulted in the minimum resistivity of 8.5 × 10⁻⁴ Ω-cm and a transmittance of 91.7%. However, a high doping concentration of 3 wt% of Al₂O₃ and excessive sputtering power over 40 W may induce high defect density and limit the growth of small grains. Although the luminance and luminous efficiency of the cell using ZnO:Al are lower than those of the cell with the ITO electrode by about 10%, these values are sufficient enough to be considered for the normal operation of AC PDP.     

直流磁控溅射法制备掺钛氧化锌透明导电薄膜

采用直流磁控溅射法在室温水冷玻璃衬底上制备出高质量的掺钛氧化锌(ZnO:Ti)透明导电薄膜,研究了溅射功率对ZnO:Ti薄膜结构、形貌和光电性能的影响,结果表明,溅射功率对ZnO:Ti薄膜的结构和电阻率有显著影响.XRD表明,ZnO:Ti薄膜为六角纤锌矿结构的多晶薄膜,且具有c轴择优取向.当溅射功率为130W时,实验制备的ZnO:Ti薄膜的电阻率具有最小值9.67×10~(-5)Ω·cm.实验制备的ZnO:Ti薄膜具有良好的附着性能,可见光区平均透过率超过91%.ZnO:Ti薄膜可以用作薄膜太阳能电池和液晶显示器的透明电极.     

Sputter deposition of ZnO thin films at high substrate temperatures

ZnO thin films have been deposited on GaN and ZnO substrates at substrate temperatures up to 750 °C by radio-frequency sputtering using ZnO ceramic targets in pure argon or in a mixture of argon and oxygen. By optimizing the sputter parameters, such as sputtering power, Ar/O₂ sputtering gas ratio and temperature of the substrates high quality films were obtained as judged from the X-ray rocking curve half width and luminescence line width. The crystallinity of the ZnO films increases with increasing substrate temperature. Yet there are distinct differences between films grown on GaN templates and on O- and Zn-polar ZnO substrates.     

层数变化对ZnO/In_2O_3多层膜微观结构及光电性能的影响

用直流磁控溅射和热氧化法在玻璃衬底上制备ZnO/In2O3透明导电多层膜,当总厚度一定时,调节溅射沉积的层数与相应各层膜的厚度,研究该多层膜微观结构、光学性能和电学性能的变化.XRD和SEM分析表明:随着溅射沉积层数的增加,In2O3衍射峰的强度不断地减弱,ZnO衍射峰出现了不同的晶面择优取向;多层膜表面的ZnO晶粒粒径变小,光洁度增加.四探针法方块电阻测试表明:低温热氧化时,ZnO/In2O3多层膜的方块电阻随层数的增加而上升;高温氧化时,ZnO/In2O3多层膜的方块电阻随层数的增加而下降.可见光光谱分析表明:随着溅射沉积层数的增加,ZnO/In2O3多薄膜在可见光区的平均透过率增大,透过率的峰值向短波方向偏移.     

纳米Ag夹层ZnO薄膜的光电性能

用射频磁控溅射ZnO陶瓷靶、直流磁控溅射Ag靶的方法在室温下制备了Ag纳米夹层结构ZnO薄膜．用X射线衍射仪、紫外一可见分光光度计、四探针电阻测量仪和原子力显微镜对薄膜样品的结构、光学透过率、面电阻和表面形貌进行表征．结果表明,ZnO衬底有利于Ag夹层形成连续膜．随着Ag层厚度的增加,Ag夹层ZnO薄膜呈现多晶结构,Ag（111）衍射峰强度增强,面电阻先迅速下降后缓慢下降．随着ZnO膜厚度的增加,Ag夹层ZnO薄膜的透射峰红移．制得样品的最佳可见光透过率高达92．3％,面电阻小于4．2Ω／□．     

In situ and ex situ investigation on the annealing performance of the ZnO film grown by ion beam deposition

The effects of the post-annealing treatment on the properties of the ZnO thin films deposited by ion beam sputtering have been investigated. By using in situ X-ray diffraction technique, an overview of the crystallization behavior of the ZnO film during the annealing process was obtained. It was found that the whole process can be divided into three regions. The improvement of the film’s crystallinity performance mainly occurs within the annealing temperature ranging from 300 to 600 °C. Both in situ and ex situ XRD results show the shift of the ZnO (002) peak towards high angle with the increasing annealing temperature, which is attributed to the variation of the stress in the film. The stress is mainly caused by the intrinsic stress which is affected by the oxygen deficiency in the film. The oxygen deficiency is sensitive to the annealing ambient. The film annealed in the O₂ ambient has less oxygen deficiency and higher resistivity. All the ZnO films deposited on the glass substrates have an optical transmittance over 85% in the visible region. Our results show that the ZnO films deposited using ion beam sputtering exhibit good thermal stability and high performance after annealing.     

直流磁控溅射功率对溅射生长GZO薄膜光电性能的影响

本文采用直流磁控溅射沉积系统在玻璃基底上沉积镓掺杂氧化锌(GZO)薄膜,将溅射功率从120W调整到240W,步长为30W,研究功率变化对GZO薄膜的晶体结构、表面形貌、光学性能和电学性能的影响。结果表明,溅射功率对GZO薄膜电阻率有显著的影响。溅射功率为210W时薄膜呈现最低电阻率为3.31×10~(-4)Ω·cm,可见光波段平均光学透光率接近84%。随着溅射功率的增加,薄膜表面形貌和生长形态发生较大变化,并直接得到具有一定凸凹不平的微结构,GZO薄膜的致密性先增加后降低。     

Optical and electrical properties of ZnO films prepared by high rate sputtering

A new compressed magnetic field (CMF) magnetron sputtering technique is described. The radiation damage undergone by the substrate during the deposition of ZnO films is determined from the capacitance-voltage characteristics of metal/ZnO/SiO₂/Si structures and etch-back metal/oxide/semiconductor structures. These characteristics are compared with those of films prepared by conventional d.c. sputtering and it is shown that the CMF magnetron sputtering technique produces films with very low radiation damage at a very high deposition rate (10 μm h^-1). The optical properties of the ZnO films were measured by investigating the propagation of an He-Ne laser beam in the waveguide mode. The propagation loss was less than 10 dB cm^-1.     

Asymmetric Bipolar Pulsed DC

Summary The use of reactive DC sputtering of insulators from conductive targets has been limited due to the intrinsic problem of target poisoning and the consequent process instabilities. As technology pushes forward, the need to rapidly deposit high quality dielectric films is becoming increasingly important. Asymmetric bi-polar pulsed DC enables existing PVD tools to produce the high quality, low defect dielectric films needed for next generation processes. Typical films produced with asymmetric bipolar pulsed DC reactive sputtering from metallic targets include: Al₂O₃, AIN, SiO₂, SiN, Ta₂O₅, DLC, BST, TaN, TiN and ITO.     

Photocatalytic Zn-doped TiO2 films prepared by DC reactive magnetron sputtering

Zn-doped TiO₂ films were prepared by means of pulsed DC reactive magnetron sputtering method using Ti and Zn mixed target. The deposition condition was optimized to produce uniform and transparent TiO₂ films. Titanium was in the Ti⁴⁺ oxidation state in all Zn-doped TiO₂ films. The zinc oxide deposited on the substrate was in the fully oxidized state of ZnO. Increase of zinc concentration inhibited the crystal growth in the TiO₂ films. The surface morphology gradually changed from crystalline to amorphous along with the increase of doped zinc concentration. The optical transmittances of these films decreased only slightly with increasing zinc concentration due to very similar band edges of ZnO and anatase TiO₂. The doped ZnO had weak influence on light absorption of the TiO₂ films. When zinc concentration was very low (<1 at%), the photocatalytic activities of the doped films had nearly no difference from that of pure TiO₂ film. Photocatalytic activities decreased obviously in the films containing high amount of zinc oxide.     

ZnO/Cu/ZnO multilayer films: Structure optimization and investigation on photoelectric properties

A series of ZnO/Cu/ZnO multilayer films has been fabricated from zinc and copper metallic targets by simultaneous RF and DC magnetron sputtering. Numerical simulation of the optical properties of the multilayer films has been carried out in order to guide the experimental work. The influences of the ZnO and Cu layer thicknesses, and of O₂/Ar ratio on the photoelectric and structural properties of the films were investigated. The optical and electrical properties of the multilayers were studied by optical spectrometry and four point probe measurements, respectively. The structural properties were investigated using X-ray diffraction. The performance of the multilayers as transparent conducting coatings was compared using a figure of merit. In experiments, the thickness of the ZnO layers was varied between 4 and 70 nm and those of Cu were between 8 and 37 nm. The O₂/Ar ratios range from 1:5 to 2:1. Low sheet resistance and high transmittance were obtained when the film was prepared using an O₂/Ar ratio of 1:4 and a thickness of ZnO (60 nm)/Cu (15 nm)/ZnO (60 nm).     

ZnO薄膜的塞贝克效应

采用直流反应磁控溅射方法在玻璃基底上成功地沉积了C轴取向性能良好的ZnO薄膜.本文研究了C轴取向性良好的ZnO薄膜在光学方面的一些性质以及ZnO薄膜的塞贝克效应,并从理论上进行了分析.     

Abscheidung von SiOxNy Sperrschichten durch Dual Magnetron Sputtering

Silicon Oxynitride Barrier Layers Deposited by Pulsed‐DC Dual Magnetron Sputtering SiO_xN_y barrier layers have been deposited using pulsed direct current (DC) and medium frequency (MF) sputtering on large area (GEN 5) glass substrates. Several process parameters, such as discharge voltage, boost voltage, and discharge frequency were varied with the goal of increasing system productivity and reducing the arc rate during SiO_xN_y deposition. The arc rate during operation with pulsed DC dual magnetron sputtering was lower than for MF sputtering; however for the same nominal discharge power, the deposition rate using pulsed DC power supplies was slightly lower than for operation with MF. The suitability for use as a barrier layer was deduced by capping the SiO_xN_y layers with DC sputtered ZnO:Al coatings and subjecting the sample stacks to anodic and cathodic degradation and subsequent storage in a damp atmosphere.     

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.     

Transparent p/n diode device from a single zinc nitride sputtering target

Zinc oxide (ZnO) thin films showing bipolar conductivity were fabricated by sputtering of zinc nitride target in plasma containing mixture of Ar-O₂ gasses. Sputtering in pure Ar plasma produced conductive and opaque zinc nitride (ZnN) films while upon introduction of oxygen up to 30% into the plasma highly transparent single phase polycrystalline n-type ZnO films have been grown. ZnN sputtering in Ar plasma containing more than 30% oxygen produced p-type ZnO films. Hall-effect and photoluminescence measurements revealed the presence of zinc vacancies and nitrogen which are acting as acceptor dopants in p-type ZnO. A heterostructure was fabricated in a single deposition run consisting of n-ZnN and p-ZnO which exhibited rectifying behavior with 2-2.5 V turn-on voltage. Improvements on the formed p/n heterostructure as well as the potential of using single sputtering target in fabrication of Zn-based homo- and hetero-junctions are discussed.     

在p-Si(100)上溅射法生长ZnO的结构和光学特性

室温下在ｐ－Ｓｉ（１００）上采用直流反应磁控溅射法外延生长了ＺｎＯ薄膜。ＸＲＤ测量表明了ＺｎＯ是高度ｃ轴单一取向生长的,ＸＲＣ测量则表明了ＺｎＯ的高质量在室温下的ＰＬ测量中见到了带边发射,其强度与晶体质量有关。