Preparation and characterization of ZnO thin films prepared by thermal oxidation of evaporated Zn thin films

In this paper, the experimental results regarding some structural, electrical and optical properties of ZnO thin films prepared by thermal oxidation of metallic Zn thin films are presented.Zn thin films (d=200–400 nm) were deposited by thermal evaporation under vacuum, onto unheated glass substrates, using the quasi-closed volume technique. In order to obtain ZnO films, zinc-coated glass substrates were isochronally heated in air in the 300–660 K temperature range, for thermal oxidation.X-ray diffraction (XRD) studies revealed that the ZnO films obtained present a randomly oriented hexagonal nanocrystalline structure. Depending on the heating temperature of the Zn films, the optical transmittance of the ZnO films in the visible wavelength range varied from 85% to 95%. The optical band gap of the ZnO films was found to be about 3.2 eV. By in situ studying of the temperature dependence of the electrical conductivity during the oxidation process, the value of about 2×10⁻² Ω⁻¹ m⁻¹ was found for the conductivity of completely oxidized ZnO films.     

Structural and electrical properties of zinc oxides thin films prepared by thermal oxidation

We report on zinc oxide (ZnO) thin films (d = 55-120 nm) prepared by thermal oxidation, at 623 K, of metallic zinc films, using a flash-heating method. Zinc films were deposited in vacuum by quasi-closed volume technique onto unheated glass substrates in two arrangements: horizontal and vertical positions relative to incident vapour. Depending on the preparation conditions, both quasi-amorphous and (0 0 2) textured polycrystalline ZnO films were obtained. The surface morphologies were characterized by atomic force microscopy and scanning electron microscopy. By in situ electrical measurements during two heating-cooling cycles up to a temperature of 673 K, an irreversible decrease of electrical conductivity of as flash-oxidized Zn films was revealed. The influence of deposition arrangement and oxidation conditions on the structural, morphological and electrical properties of the ZnO films is discussed.     

电化学沉积高c轴取向ZnO薄膜及其光学性能分析

采用阴极还原方法,在透明导电玻璃(ITO)上制备了高c轴择优取向的ZnO薄膜.通过X射线衍射、扫描电子显微镜等表征技术,研究了沉积电流对ZnO薄膜的结构、应力状态及表面形貌的影响;利用光致荧光光谱及透射光谱等分析方法,探讨了沉积电流变化对ZnO薄膜的光学性能的影响.研究结果显示:各沉积电流下均可制得高c轴取向的ZnO薄膜;薄膜表面形貌受电流的影响较大;从透射谱可以看出,薄膜在可见光波段有较高透射率,且薄膜厚度随沉积电流的增大而增大.光致荧光测量表明,电化学沉积的ZnO薄膜具有明显的带隙展宽.而且,随着沉积电流的增加,带隙发光强度逐渐减弱,缺陷发光逐渐增强.     

Ultraviolet detectors based on ZnO films by thermal oxidation of Zn metallic films

Metallic Zn films were deposited on glass substrates by electron-beam evaporation. ZnO films were synthesized by thermal oxidation of Zn metallic films in air. At the annealing temperature of 550 °C, ZnO nanowires appeared on the surface, which mainly result from the decrease of oxidation rate. A ZnO ultraviolet photodetector was fabricated based on a metal-semiconductor-metal planar structure. The detector showed a large UV photoresponse with an increase of two orders of magnitude. It is concluded that promising UV detectors can be obtained on ZnO films by thermal oxidation of Zn metallic films. The ways of performing spectral response measurements for polycrystalline ZnO films are also discussed.      

衬底对原位氧化制备的ZnO薄膜结构和光学性质的影响

采用射频反应溅射法在不同衬底上制备Zn3N2薄膜,然后对其原位氧化制备ZnO薄膜。利用X射线衍射分析(XRD)、扫描电子显微镜(SEM)和光致发光谱(PL)等表征技术研究了不同衬底对ZnO薄膜的结晶特性和发光性能的影响。XRD研究结果显示:Zn3N2薄膜在500 ℃原位氧化3 h后完全转变为ZnO薄膜,在玻璃和熔融石英衬底上制备的多晶ZnO薄膜无择优取向,而单晶硅（100）衬底上的多晶ZnO薄膜具有较好的沿（002）方向的择优取向。PL测试结果显示:硅和熔融石英衬底上的多晶ZnO薄膜发光性能良好,激子复合产生的紫外发光峰很强,且半高宽较窄,而来自于深能级发射的绿色发光峰很弱;而玻璃衬底上的多晶ZnO薄膜发光性能较差。     

衬底对原位氧化制备的ZnO薄膜结构和光学性质的影响

 采用射频反应溅射法在不同衬底上制备Zn₃N₂薄膜,然后对其原位氧化制备ZnO薄膜。利用X射线衍射分析(XRD)、扫描电子显微镜(SEM)和光致发光谱(PL)等表征技术研究了不同衬底对ZnO薄膜的结晶特性和发光性能的影响。XRD研究结果显示:Zn₃N₂薄膜在500 ℃原位氧化3 h后完全转变为ZnO薄膜,在玻璃和熔融石英衬底上制备的多晶ZnO薄膜无择优取向,而单晶硅（100）衬底上的多晶ZnO薄膜具有较好的沿（002）方向的择优取向。PL测试结果显示:硅和熔融石英衬底上的多晶ZnO薄膜发光性能良好,激子复合产生的紫外发光峰很强,且半高宽较窄,而来自于深能级发射的绿色发光峰很弱;而玻璃衬底上的多晶ZnO薄膜发光性能较差。     

Structural characterization of supported nanocrystalline ZnO thin films prepared by dip-coating

Nanocrystalline ZnO thin films prepared by the sol-gel dip-coating technique were characterized by grazing incidence X-ray diffraction (GIXD), atomic force microscopy (AFM), X-ray reflectivity (XR) and grazing incidence small-angle X-ray scattering (GISAXS). The structures of several thin films subjected to (i) isochronous annealing at 350, 450 and 550 °C, and (ii) isothermal annealing at 450 °C during different time periods, were characterized. The studied thin films are composed of ZnO nanocrystals as revealed by analysing several GIXD patterns, from which their average sizes were determined. Thin film thickness and roughness were determined from quantitative analyses of AFM images and XR patterns. The analysis of XR patterns also yielded the average density of the studied films. Our GISAXS study indicates that the studied ZnO thin films contain nanopores with an ellipsoidal shape, and flattened along the direction normal to the substrate surface. The thin film annealed at the highest temperature, T = 550 °C, exhibits higher density and lower thickness and nanoporosity volume fraction, than those annealed at 350 and 450 °C. These results indicate that thermal annealing at the highest temperature (550 °C) induces a noticeable compaction effect on the structure of the studied thin films.     

Blue luminescence from Ce-doped ZnO thin films prepared by magnetron sputtering

The photoluminescence properties of undoped and Ce-doped ZnO thin films that were prepared by DC magnetron sputtering were investigated. It was found that the incorporation of Ce could intensively affect the structural, optical, and photoluminescence properties of the ZnO thin films. The undoped ZnO thin films showed a sharp UV luminescence, whereas the Ce-doped ZnO thin films showed a broad blue luminescence. The effects of excitation wavelength and annealing atmosphere on the photoluminescence properties of Ce-doped ZnO thin films were also studied. After post-annealing in air and oxygen atmospheres, the blue emissions of the prepared films were drastically suppressed. Our results indicate that the blue emissions of Ce-doped ZnO thin films are related to zinc interstitials and the intrinsic transition of Ce³⁺ ions.     

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.     

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.     

Room temperature chemical synthesis of lead selenide thin films with preferred orientation

Room temperature chemical synthesis of PbSe thin films was carried out from aqueous ammoniacal solution using Pb(CH₃COO)₂ as Pb²⁺ and Na₂SeSO₃ as Se²⁻ ion sources. The films were characterized by a various techniques including, X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), Fast Fourier transform (FFT) and UV-vis-NIR techniques. The study revealed that the PbSe thin film consists of preferentially oriented nanocubes with energy band gap of 0.5 eV.     

Excimer laser processing of ZnO thin films prepared by the sol-gel process

ZnO thin films were prepared on soda-lime glass from a single spin-coating deposition of a sol-gel prepared with anhydrous zinc acetate [Zn(C₂H₃O₂)₂], monoethanolamine [H₂NC₂H₄OH] and isopropanol. The deposited films were dried at 50 and 300 °C. X-ray analysis showed that the films were amorphous. Laser annealing was performed using an excimer laser. The laser pulse repetition rate was 25 Hz with a pulse energy of 5.9 mJ, giving a fluence of 225 mJ cm⁻² on the ZnO film. Typically, five laser pulses per unit area of the film were used. After laser processing, the hexagonal wurtzite phase of zinc oxide was observed from X-ray diffraction pattern analysis. The thin films had a transparency of greater than 70% in the visible region. The optical band-gap energy was 3.454 eV. Scanning electron microscopy and profilometry analysis highlighted the change in morphology that occurred as a result of laser processing. This comparative study shows that our sol-gel processing route differs significantly from ZnO sol-gel films prepared by conventional furnace annealing which requires temperatures above 450 °C for the formation of crystalline ZnO.     

Controlled visible photoluminescence of ZnO thin films prepared by RF magnetron sputtering

ZnO thin films were prepared by RF magnetron sputtering. The photoluminescence dependence on the growth ambient and annealing temperatures and the atmosphere has been studied. Visible photoluminescence with blue, green, orange, and red emission bands has been demonstrated by controlling the preparation conditions. Complete suppression of the visible emission bands was also realized by annealing the O₂-ambient-grown samples in N₂ atmosphere at higher temperatures, which indicated the preparation of ZnO thin films with high optical quality.     

Properties of Dy-doped ZnO nanocrystalline thin films prepared by pulsed laser deposition

Highly transparent conductive Dy₂O₃ doped zinc oxide (ZnO)_1-x(Dy₂O₃)_x nanocrystalline thin films with x from 0.5% to 5% have been deposited on glass substrate by pulsed laser deposition technique. The structural, electrical and optical properties of Dy₂O₃ doped thin films were investigated as a function of the x value. The experimental results show that the Dy concentration in Dy-doped ZnO thin films has a strong influence on the material properties especially electrical properties. The resistivity decreased to a minimum value of 5.02 × 10⁻⁴ Ω cm with x increasing from 0.5% to 1.0%, then significantly increased with the further increasing of x value. On the contrary, the optical direct band gap of the (ZnO)_1-x(Dy₂O₃)_x films first increased, then decreased with x increasing. The average transmission of Dy₂O₃ doped zinc oxide films in the visible range is above 90%.     

Crystalline orientation and growth in ferrite thin films prepared by cathodic sputtering

We have prepared, by cathodic sputtering, single crystal ferrite films by epitaxial growth on MgO substrates, for a wide range of sputtering parameters. In a general manner, it is necessary to change in the sputtering chamber the oxygen pressure according to the temperature of the growing ferrite film. Thin films are studied by electron diffraction and results obtained are completed by observation of C.Pt replicas. The growth of single crystal ferrite films is discussed in comparison with polycrystalline films deposited on amorphous substrates: the growing facies is a function of both temperature and oxygen partial pressure.     

Optical properties of zinc phthalocyanine thin films prepared by pulsed laser deposition

ZnPc thin films were prepared by pulsed laser deposition (KrF laser, λ = 248 nm, τ = 5 ns, f = 50 Hz) on suprasil substrates in vacuum. Optical properties in UV–Vis spectral region were analyzed as functions of laser fluence from 40 to 100 mJ/cm² by spectrophotometric and spectral ellipsometry measurements. The spectral ellipsometry data were treated using a three-layer model (substrate, film, roughness). The best results of data fitting were obtained when Q band was characterized by two Lorentz oscillators, while two Gaussian oscillators were used for B and C band fitting. We derived the band gap using Tauc plot considering ZnPc a direct band gap semiconductor. The band gap values were found decreasing from 3.13 to 3.09 eV with increasing laser fluence, which might be related with formation of trapping sites at higher fluence.     

Mn doped ZnO nanostructured thin films prepared by ultrasonic spray pyrolysis method

Mn-doped ZnO thin films with different percentage of Mn content (0, 1, 3 and 5 at.%) and substrate temperature of 350 °C, were deposited by a simple ultrasonic spray pyrolysis method under atmospheric pressure. We have studied the structural and optical properties by using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and ultra-violet visible near infrared (UV–Vis-NIR) spectroscopy. The lattice parameters calculated for the Mn-doped ZnO from XRD pattern were found to be slightly larger than those of the undoped ZnO, which indicate substitution of Mn in ZnO lattice. Compared with the Raman spectra for ZnO pure films, the Mn-doping effect on the spectra is revealed by the presence of additional peak around 524 cm⁻¹ due to Mn incorporation. With increasing Mn doping the optical band gap increases indicating the Burstein–Moss effect.     

Strong ultraviolet emission from zinc oxide thin films prepared by electrophoretic deposition

In this paper, we report a simple and efficient method to prepare high-quality nanocrystalline ZnO films by electrophoretic deposition. Absorption spectrum and transmission electron microscope image indicated that the average size of ZnO nanoparticles is about 9.5 nm. A strong ultraviolet emission peak at 384 nm is observed and the deep-level emission band is barely observed at room temperature. X-ray diffraction pattern revealed that the ZnO film has a polycrystalline hexagonal wurtzite structure. The Raman spectrum showed a typical resonant multi-phonon process within the ZnO film. The frequency shift of 1 LO phonon was about 583 cm⁻¹.     

溶胶凝胶旋转涂敷技术制备ZnO:In薄膜的结构特性

采用溶胶凝胶法,结合旋转涂敷技术在石英衬底上制备了210—240nm厚度的ZnO∶In薄膜.使用掠角入射X射线衍射(GI_XRD)、常规X射线衍射、傅里叶变换红外光谱、原子力显微镜、光致发光谱以及不同入射角GI_XRD谱(α=1,2,3和5°)等手段,对不同掺杂浓度的ZnO∶In薄膜进行了结构分析.发现ZnO∶In薄膜内部是由大尺寸(002)晶向的无应力ZnO晶粒堆积而成,而薄膜表面主要是小尺寸的(002)和(103)晶粒,并且适量的In掺杂能有效改善ZnO薄膜内部的晶体结构特性. 关键词： ZnO∶In薄膜 晶体结构 掠角入射X射线衍射 溶胶凝胶法