Optimization of parameters for deposition of Ga-doped ZnO films by DC reactive magnetron sputtering using Taguchi method

Ga-doped ZnO (ZnO:Ga) transparent conductive films were deposited on glass substrates by DC reactive magnetron sputtering. Taguchi method was used to find the optimal deposition parameters including oxygen partial pressure, argon partial pressure, substrate temperature, and sputtering power. By employing the analysis of variance, we found that the oxygen and argon partial pressures were the most influencing parameters on the electrical properties of ZnO:Ga films. Under the optimized deposition conditions, the ZnO:Ga films showed acceptable crystal quality, lowest electrical resistivity of 2.61 × 10⁻⁴ Ω cm, and high transmittance of 90% in the visible region.     

Growth characteristics and properties of ZnO:Ga thin films prepared by pulsed DC magnetron sputtering

Transparent conductive ZnO:Ga thin films were deposited on Corning 1737 glass substrate by pulsed direct current (DC) magnetron sputtering. The effects of process parameters, namely pulse frequency and film thickness on the structural and optoelectronic properties of ZnO:Ga thin films are evaluated. It shows that highly c-axis (0 0 2) oriented polycrystalline films with good visible transparency and electrical conductivity were prepared at a pulsed frequency of 10 kHz. Increasing the film thickness also enlarged the grain size and carrier mobility which will subsequently lead to the decrease in resistivity. In summary, ZnO:Ga thin film with the lowest electrical resistivity of 2.01 × 10⁻⁴ Ω cm was obtained at a pulse frequency of 10 kHz with 500 nm in thickness. The surface RMS (root mean square) roughness of the film is 2.9 nm with visible transmittance around 86% and optical band gap of 3.83 eV.     

Transparent conductive and near-infrared reflective Cu-based Al-doped ZnO multilayer films grown by magnetron sputtering at room temperature

Cu-based Al-doped ZnO multilayer films were deposited on glass substrates by DC magnetron sputtering at room temperature. Three kinds of multilayer structures (AZO/Cu, AZO/Cu/AZO, and Cu/AZO) were designed for comparison, and the effects of the Cu layer thickness on photoelectrical properties of the multilayer films were investigated. The results revealed that the transparent-conductive property and near-infrared reflectance of the films are closely correlated with the Cu layer thickness, and among the three structures, AZO/Cu bi-layer films exhibited preferable photoelectrical properties. The AZO/Cu bi-layer film with a Cu layer thickness of 7 nm displayed the highest figure of merit of 4.82 × 10⁻³ Ω⁻¹, with a low sheet resistance of 21.7 Ω/sq and an acceptable visible transmittance of 80%. The near infrared reflectance above 50% can be simultaneously obtained. The good performance of the coatings indicates that they are promising for coated glasses, thin film solar cells and heat-reflectors.     

Characteristics of ZnO:In thin films prepared by RF magnetron sputtering

In-doped ZnO (ZnO:In) transparent conductive thin films were deposited on glass substrates by RF magnetron sputtering. The effect of substrate temperature on the structural, electrical and optical properties of the ZnO:In thin films was investigated. It was found that higher temperature improves the crystallinity of the films and promotes In substitution easily. ZnO:In thin films with the best crystal quality were fabricated at 300 °C, which exhibit a larger grain size of 29 nm and small tensile strain of 0.9%. The transmittance of all the films was revealed to be over 85% in the visible range independence of the substrate temperatures and the lowest resistivity of ZnO:In thin films is 2.4×10⁻³ Ω cm.     

衬底温度对反应磁控溅射W掺杂ZnO薄膜的微观结构及光电性能的影响

采用直流脉冲反应磁控溅射方法生长W掺杂ZnO（WZO）透明导电氧化物薄膜并研究了衬底温度对薄膜微观结构、组分、表面形貌以及光电性能的影响.实验结果表明,WZO薄膜具有良好的（002）晶面择优取向,且适当的衬底温度是制备优质WZO薄膜的关键因素.随着衬底温度升高,薄膜表面粗糙度先增大后减小;衬底温度较高时,薄膜的结构致密,结晶质量好,电子迁移率高.当衬底温度为325℃时,WZO薄膜获得最低电阻率9.25×10^-3Ω·cm,方块电阻为56.24Ω/□,迁移率为11.8 cm² V^-1·s^-1,其在可见光及近红外区域（400—1500 nm）范围的平均透过率达到85.7%.     

直流磁控溅射制备氧化钒薄膜

讨论了在低温下以高纯金属钒作靶材,用直流磁控溅射的方法制备出了氧化钒薄膜。通过设计正交试验,分析了氩气和氧气的流量比,溅射功率,工作压强,基底温度对氧化钒薄膜沉积速率和电阻温度系数TCR的影响,采用RTP-500型快速热处理机对氧化钒薄膜样品进行了退火热处理,实验结果表明:当Ar与O2的比例为100:4,溅射功率为120W,工作压强为2Pa时,所获得薄膜TCR较大,都在-2%/K附近,最高的可达-3.6%/K。     

Influence of negative ion resputtering on Al-doped ZnO thin films prepared by mid-frequency magnetron sputtering

Al-doped ZnO (AZO) films were deposited on glass substrates by mid-frequency magnetron sputtering with a ceramic ZnO:Al₂O₃ (98 wt%:2 wt%) target. The origin of the high resistivity of the films at the substrate position facing the erosion area of the target was investigated. The results indicate a preferential resputtering of Zn atoms caused by the negative ions, which leads to an increase of the oxygen/metal ratio in the films. Then more Al oxides form and result in the decrease of Al_Zn (the main donor in the films) concentration in the films. Thus the free carrier concentration decreases badly. This is the main mechanism responsible for the high resistivity.     

The influence of annealing on the properties of ZnO:Al layers obtained by RF magnetron sputtering

Al doped ZnO has been explored as a viable alternative to indium thin oxide, which is usually used as transparent electrodes' coverage but is expensive. Homogenous and durable ZnO:Al layers on glass have been obtained in radio frequency magnetron sputtering system by adjusting optimized deposition parameters, using ZnO ceramic target with 2?wt% Al₂O₃. Then, after growth process, annealing treatment has been introduced in order to improve the quality of the layers. Structural, electrical and optical properties of the obtained ZnO:Al layers are presented and discussed. From the application point of view, the best results (sheet resistance of 24 Ω/sq and transparency well above 85%) were achieved after annealing in 300?°C.     

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.     

Defects related room temperature ferromagnetism in p-type (Mn, Li) co-doped ZnO films deposited by reactive magnetron sputtering

We report on the defects related room temperature ferromagnetic characteristics of Zn_0.95-xMn_xLi_0.05O (x = 0.01, 0.03, 0.05 and 0.08) thin films grown on glass substrates using reactive magnetron sputtering. By increasing the Mn content, the films exhibited increases in the c-axis lattice constant, fundamental band gap energy, coercive field and remanent magnetization. Comparison of the structural and magnetic properties of the as-deposited and annealed films indicates that the hole carriers, together with defects concentrations, play an important role in the ferromagnetic origin of Mn and Li co-doped ZnO thin films. The ferromagnetism in films can be described by bound magnetic polaron models with respect to defect-bound carriers.     

The field emission of indium-doped ZnO films fabricated by room temperature DC magnetron sputtering

Indium doped ZnO film was fabricated at room temperature by co-sputtering a zinc target and an indium plate under the flow of oxygen and argon. The film was then characterized and the field emission of the film was studied. The indium composition x in the film (Zn_1−xIn_xO) is 5%. The film is hexagonal without any secondary phases or precipitates. The film has two major emission peaks, one related to the band edge emission and another possibly related to the electron acceptor transition. The possible acceptor is nitrogen occupying oxygen site in ZnO. The film is n-type and very resistive. The turn on field of the film at an emission current density of 10 μA/cm² is 17.5 V/μm. The relatively weak field emission property is due to the unintentional incorporation of acceptors such as substitutional nitrogen and oxygen vacancies, which increase the work function of ZnO by reducing the electron density and lowering the Fermi level position of the ZnO:In film.     

Low-temperature deposition of transparent conducting ZnO:Zr films on PET substrates by DC magnetron sputtering

Transparent conducting zirconium-doped zinc oxide (ZnO:Zr) films were firstly deposited on polyethylene terephthalate (PET) substrates with ZnO buffer layers by DC magnetron sputtering at room temperature. Dependence of physical properties of ZnO:Zr films on deposition pressure was systematically studied. All the deposited films were polycrystalline and (1 0 0) oriented. When deposition pressure increases from 1 to 2.5 Pa, the crystallinity of the films improves and the resistivity decreases. While deposition pressure increases from 2.5 to 3.5 Pa, the crystallinity of the films deteriorates and the resistivity increases. The lowest resistivity of 1.8 × 10⁻³ Ω cm was obtained for the films deposited at the optimum deposition pressure of 2.5 Pa. All the films present a high transmittance of above 86% in the wavelength range of the visible spectrum.     

Deposition of Ni, Ag, and Pt-based Al-doped ZnO double films for the transparent conductive electrodes by RF magnetron sputtering

Ni, Ag, and Pt-based Al-doped ZnO (AZO) films have been deposited as transparent conductivity layers on quartz by RF magnetron sputtering and characterized by X-ray diffraction, Hall measurement, optical transmission spectroscopy, scanning electron microscopy (SEM). The deposition of thicker metal layer in double layers resulted in lowering the effective electrical resistivity with a slight reduction of their optical transmittance. A film consisting of AZO (250 nm)/Ni (2 nm) double structure, exhibits a sheet resistance of 21.0 Ω/sq, a high transmittance of 76.5%, and characterize good adhesion to substrate. These results make the satisfactory for GaN-based light-emitting diodes (LEDs) and solar cells with metal-based AZO double films as current spread layers.     

Structural and electrical properties of fluorine-doped zinc tin oxide thin films prepared by radio-frequency magnetron sputtering

Transparent and conductive thin films of fluorine doped zinc tin oxide (FZTO) were deposited on glass substrates by radio-frequency (RF) magnetron sputtering using a 30 wt% ZnO with 70 wt% SnO₂ ceramic targets. The F-doping was carried out by introducing a mixed gas of pure Ar, CF₄, and O₂ forming gas into the sputtering chamber while sputtering ZTO target. The effect of annealing temperature on the structural, electrical and optical performances of FZTO thin films has been studied. FZTO thin film annealed at 600 °C shows the decrease in resistivity 5.47 × 10⁻³ Ω cm, carrier concentration ∼10¹⁹ cm⁻³, mobility ∼20 cm² V⁻¹ s⁻¹ and an increase in optical band gap from 3.41 to 3.60 eV with increasing the annealing temperatures which is well explained by Burstein–Moss effect. The optical transmittance of FZTO films was higher than 80% in all specimens. Work function (ϕ) of the FZTO films increase from 3.80 eV to 4.10 eV through annealing and are largely dependent on the amounts of incorporated F. FZTO is a possible potential transparent conducting oxide (TCO) alternative for application in optoelectronics.     

Surface textured ZnO:Al thin films by pulsed DC magnetron sputtering for thin film solar cells applications

Transparent conducting thin films of ZnO:Al (Al-doped ZnO, AZO) were prepared via pulsed DC magnetron sputtering with good transparency and relatively lower resistivity. The AZO films with 800 nm in thickness were deposited on soda-lime glass substrates keeping at 473 K under 0.4 Pa working pressure, 150 W power, 100 μs duty time, 5 μs pulse reverse time, 10 kHz pulse frequency and 95% duty cycle. The as-deposited AZO thin films has resistivity of 6.39 × 10⁻⁴ Ω cm measured at room temperature with average visible optical transmittance, T_total of 81.9% under which the carrier concentration and mobility were 1.95 × 10²¹ cm⁻³ and 5.02 cm² V⁻¹ s⁻¹, respectively. The films were further etched in different aqueous solutions, 0.5% HCl, 5% oxalic acid, 33% KOH, to conform light scattering properties. The resultant films etched in 0.5% HCl solution for 30 s exhibited high T_total = 78.4% with haze value, H_T = 0.1 and good electrical properties, ρ = 8.5 × 10⁻⁴ Ω cm while those etched in 5% oxalic acid for 150 s had desirable H_T = 0.2 and relatively low electrical resistivity, ρ = 7.9 × 10⁻⁴ Ω cm. However, the visible transmittance, T_total was declined to 72.1%.     

Influence of deposition temperature on the crystallinity of Al-doped ZnO thin films at glass substrates prepared by RF magnetron sputtering method

Al-doped ZnO (AZO) transparent conducting films were successfully prepared on glass substrates by RF magnetron sputtering method under different substrate temperatures. The microstructural, electrical and optical properties of AZO films were investigated in a wide temperature range from room temperature up to 350 °C by X-ray Diffraction (XRD), Field-Emission Scanning Electron Microscopy (FESEM), High-Resolution Transmission Electron Microscopy (HRTEM), Hall measurement, and UV–visible meter. The nature of AZO films is polycrystalline thin films with hexagonal wurtzite structure and a preferred orientation along c-axis. The crystallinity and surface morphologies of the films are strongly dependent on the growth temperature, which in turn exerts a great effect on microstructural, electrical and optical properties of the AZO films. The atomic arrangement of AZO film having an wurtzite structure was indeed identified by the HRTEM as well as the Selected Area Electron Diffraction (SAED). The defect density of AZO film was investigated by HRTEM. The film deposited at 100 °C exhibited the relatively well crystallinity and the lowest resistivity of 3.6 × 10⁻⁴ Ω cm. The average transmission of AZO films in the visible range is all over 85%. More importantly, the low-resistance and high-transmittance AZO film was also prepared at a low temperature of 100 °C.     

Dependences of structural and electrical properties on thickness of polycrystalline Ga-doped ZnO thin films prepared by reactive plasma deposition

Polycrystalline Ga-doped (Ga content: 4 wt%) ZnO (GZO) thin films were deposited on glass substrates at 200 C by a reactive plasma deposition with DC arc discharge technique. The dependences of structural and electrical properties of GZO films on thickness, ranging from 30 to 560 nm, were investigated. Carrier concentration, n, and Hall mobility, μ, increases with increasing film thickness below 100 nm, and then the n remains nearly constant and the μ gradually increases until the thickness reaches 560 nm. The resistivity obtained of the order of 10⁻⁴ Ω cm for these films decreases with increasing film thickness: The highest resistivity achieved is 4.4×10⁻⁴ Ω cm with n of 7.6×10²⁰ cm⁻³ and μ of 18.5 cm²/V s for GZO films with a thickness of 30 nm and the lowest one is 1.8×10⁻⁴ Ω cm with n of 1.1×10²¹ cm⁻³ and μ of 31.7 cm²/V s for the GZO film with a thickness of 560 nm. X-ray diffraction pattern for all the films shows a hexagonal wurtzite structure with its strongly preferred orientation along the c-axis. Full width at half maximum of the (002) preferred orientation diffraction peak of the films decreases with increasing film thickness below 100 nm.     

直流反应磁控溅射制备掺铟ZnO透明导电薄膜的研究

本文介绍了掺铟ZnO透明导电膜的制备工艺.并应用半导体物理理论分析了薄膜的导电机理,用Drude理论建立了物理模型,分析与计算了薄膜从可见到红外光波段的光学性能,结果表明,理论计算与实测值两者符合得较好.     

Influence of excitation light wavelength on the photoluminescence properties for ZnO films prepared by magnetron sputtering

Highly orientated polycrystalline ZnO films were deposited on sapphire, silicon and quartz substrates at room temperature by r.f. magnetron sputtering. Different photoluminescence (PL) spectra were observed when excited with different wavelength light. A UV emission peak (356 nm) and a blue peak (446 nm) were generated for the films on sapphire, silicon and quartz substrates, and only the 446 nm blue emission appeared for the films on glass substrates when the wavelength of the excitation light was 270 nm. With increasing the wavelength of the excitation light up to 300 and 320 nm, the UV emission disappeared for films on various substrates and the wavelength of the PL peaks increased up to 488 and 516 nm, respectively. When the wavelength of the excitation light increased to 398 nm, the PL spectrum becomes a wide band that is consistent with three emission peaks.     

Photoconductivity in metal-semiconductor-metal planar structures with ZnO:Ga and ZnO:Li films

Influence of UV radiation on photoelectric properties of ZnO:Ga and ZnO:Li films prepared by the electron-beam evaporation method was investigated. The photoconductivity was measured, using metal-semiconductor-metal planar structures where metallic aluminum was used as ohmic electrodes. The kinetics of rise and decay of the photoconductivity in these structures was studied. The change of photoconductivity under the action of UV radiation is considered as a result of the photoexcitation-relaxation into the conduction band and photochemical processes of absorption-desorption of oxygen at the film surface. The influence of a MgF₂ protective layer deposited on ZnO:Ga and ZnO:Li films was studied. Measurements of the spatial distribution of the potential between the anode and cathode for determination of the homogeneity of conductivity in the investigated planar structures were performed by the moving probe method.