Optical constants of Na-doped ZnO thin films by sol-gel method

The structural and optical properties of pure and Na-doped ZnO thin films have been investigated by X-ray diffraction (XRD), atom force microscopy and UV-Vis spectrophotometer. The crystal structure of all the thin films is the hexagonal wurtzite. The average grain size and surface roughness increases with the increase of the Na/Zn ratio. The optical band gap of the thin films decreases from 3.26 to 3.12 eV by increasing the Na/Zn ratio from 0.0 to 0.10. Transmittance spectra were used to determine the optical constants of the thin films, and the effect of Na/Zn ratio on the optical constants was investigated. With the increase of Na/Zn ratio, the refractive index decreases and the extinction coefficient increases in the 380-700 nm spectral range.     

Engineering of electronic and optical properties of ZnO thin films via Cu doping

ZnO thin films doped with different Cu concentrations are fabricated by reactive magnetron sputtering technique. XRD analysis indicates that the crystal quality of the ZnO:Cu film can be enhanced by a moderate level of Cu-doping in the sputtering process. The results of XPS spectra of zinc, oxygen, and copper elements show that Cu-doping has an evident and complicated effect on the chemical state of oxygen, but little effect on those of zinc and copper. Interestingly, further investigation of the optical properties of ZnO:Cu samples shows that the transmittance spectra exhibit both red shift and blue shift with the increase of Cu doping, in contrast to the simple monotonic behavior of the Burstein–Moss effect. Analysis reveals that this is due to the competition between oxygen vacancies and intrinsic and surface states of oxygen in the sample. Our result may suggest an effective way of tuning the bandgap of ZnO samples.     

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.     

The transparence comparison of Ga- and Al-doped ZnO thin films

The Ga-doped ZnO (GZO) and Al-doped ZnO (AZO) thin films were grown on quartz glass substrates by pulsed laser deposition under different oxygen partial pressures (PO₂). The transparent performances of films versus properties of structure and conductivity were discussed. With the increase of PO₂, the transmittance of both GZO films and AZO films increased to maximum and then decreased which were in according with the change of crystallization quality. The transmittance of GZO films was higher than that of AZO films, which were not dominated by the impurity ions induced by doping. AFM images and surface roughness mean square coefficients showed that the surfaces of GZO films were smoother than that of AZO films, which were due to the dopant Ga acting as the surfactant and smoothed the GZO films surface.     

Ordered ultra thin ZnO films on metal substrate

Ultra thin ZnO films were prepared on metal Mo(1 1 0) substrate under ultrahigh vacuum conditions either by depositing Zn in 10⁻⁵ Pa oxygen or by oxidizing pre-deposited Zn films. The films were characterized in situ by various surface analytical techniques, including Auger electron spectroscopy, X-ray and ultraviolet photoelectron spectroscopies, low energy electron diffraction and high resolution electron energy loss spectroscopy. The results indicate that a long-range ordered and stoichiometric ZnO films are formed along its [0 0 0 1] direction. The annealing experiments show that as-prepared ZnO films are thermal stable until 800 K. This study provides constructive information to further understand the growth mechanism of ZnO films on different substrates.     

Physical properties of ZnO thin films deposited by spray pyrolysis technique

Thin films of ZnO have been prepared on glass substrates at different thicknesses by spray pyrolysis technique using 0.2 M aqueous solution of zinc acetate. X-ray diffraction reveals that the films are polycrystalline in nature having hexagonal wurtzite type crystal structure. The resistivity at room temperature is of the order 10⁻² Ω cm and decreased as the temperature increased. Films are highly transparent in the visible region. The dependence of the refractive index, n, and extinction coefficient, k, on the wavelength for a sprayed film is also reported. Optical bandgap, E_g, has been reported for the films. A shift from E_g = 3.21 eV to 3.31 eV has been observed for deposited films.     

Effect of Mn doping on the nanostructure and optical properties of ZnO films synthesized by magnetron sputtering

We investigated the microstructure and optical properties of Zn_1−xMn_xO films synthesized by the magnetron sputtering technique. Structural analyses suggest that Mn occupied the Zn sites successfully and did not change the wurtzite structure of ZnO. In addition, nanoscale columnar grain arrays were found in the Mn-doped ZnO films. The experimental results indicate that moderate Mn doping could enhance the photoluminescence emission of ZnO. The possible origin of the emissions from our samples was also explored.     

Effects of sapphire substrates surface treatment on the ZnO thin films grown by magnetron sputtering

The surface treatment effects of sapphire substrate on the ZnO thin films grown by magnetron sputtering were studied. The sapphire substrates properties have been investigated by means of atomic force microscopy (AFM) and X-ray diffraction rocking curves (XRCs). The results show that sapphire substrate surfaces have the best quality by CMP with subsequent chemical etching. The surface treatment effects of sapphire substrate on the ZnO thin films were examined by X-ray diffraction (XRD) and photoluminescence (PL) measurements. Results show that the intensity of (0 0 2) diffraction peak of ZnO thin films on sapphire substrates treated by CMP with subsequent chemical etching was strongest, FWHM of (0 0 2) diffraction peak is the narrowest and the intensity of UV peak of PL spectrum is strongest, indicating surface treatment on sapphire substrate preparation may improve ZnO thin films crystal quality and photoluminescent property.     

Induced growth of high quality ZnO thin filmsby crystallized amorphous ZnO

This paper reports the induced growth of high quality ZnO thin film by crystallized amorphous ZnO. Firstly amorphous ZnO was prepared by solid-state pyrolytic reaction, then by taking crystallized amorphous ZnO as seeds (buffer layer), ZnO thin films have been grown in diethyene glycol solution of zinc acetate at 80℃. X-ray Diffraction curve indicates that the films were preferentially oriented [001] out-of-plane direction of the ZnO. Atomic force microscopy and scanning electron microscopy were used to evaluate the surface morphology of the ZnO thin film. Photoluminescence spectrum exhibits a strong ultraviolet emission while the visible emission is very weak. The results indicate that high quality ZnO thin film was obtained.     

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%.     

Annealing effects on electrical and optical properties of ZnO thin films synthesized by the electrochemical method

Microstructural and electrical properties of potentiostatically electrodeposited ZnO thin films from an aqueous bath were investigated after annealing at different temperatures in Ar and 5% H₂/Ar atmospheres. It is confirmed that the bandgap energy of ZnO thin films decreased with annealing from 3.42 to 3.27-3.29 eV by calculating the wavelength of the absorption region. The annealing at temperatures as low as 200 °C decreased the sheet resistance of ZnO thin films because of the extinction of Zn(OH)₂ in the atmosphere. In addition, the sheet resistance of ZnO thin films decreased by annealing in a 5% H₂ atmosphere, which caused an increase of carrier concentration by hydrogen reduction.     

Effects of deposition temperature on the structural and morphological properties of thin ZnO films fabricated by pulsed laser deposition

ZnO thin films were grown on Si(1 0 0) substrates using pulsed laser deposition in O₂ gas ambient (10 Pa) and at different substrate temperatures (25, 150, 300 and 400 °C). The influence of the substrate temperature on the structural and morphological properties of the films was investigated using XRD, AFM and SEM. At substrate temperature of T=150 °C, a good quality ZnO film was fabricated that exhibits an average grain size of 15.1 nm with an average RMS roughness of 3.4 nm. The refractive index and the thickness of the thin films determined by the ellipsometry data are also presented and discussed.     

Thermal stress induced band gap variation of ZnO thin films

The growth temperature and post annealing-dependent optical and structural effect of RF magnetron sputtered ZnO thin films were examined. As the growth temperature increased, the lattice constant increased and approached the bulk value, suggesting a decrease in interfacial strain between the substrate and thin film. For the post annealed samples, the interfacial strain decreased further and was close to the bulk value regardless of the post annealing environments (in air and O₂). The optical properties of all ZnO thin films examined and revealed higher transparency (>90%). Furthermore, the optical band gap varied according to the growth temperature and post annealing environments due to a decrease in the interfacial strain effect.     

The effects of post-thermal annealing on the optical parameters of indium-doped ZnO thin films

Indium-doped ZnO thin films are deposited on quartz glass slides by RF magnetron sputtering at ambient temper- ature. The as-deposited films are annealed at different temperatures from 400 C to 800 C in air for 1 h. Transmittance spectra are used to determine the optical parameters and the thicknesses of the films before and after annealing using a nonlinear programming method, and the effects of the annealing temperatures on the optical parameters and the thickness are investigated. The optical band gap is determined from the absorption coefficient. The calculated results show that the film thickness and optical parameters both increase first and then decrease with increasing annealing temperature from 400 C to 800 C. The band gap of the as-deposited ZnO:In thin film is 3.28 eV, and it decreases to 3.17 eV after annealing at 400 C. Then the band gap increases from 3.17 eV to 3.23 eV with increasing annealing temperature from 400 C to 800 C.     

Effect of annealing temperature on photocatalytic activity of ZnO thin films prepared by sol-gel method

Zinc oxide thin films are deposited on Si and quartz substrates using the sol-gel method. The thin films, annealed at 400, 600 and 800 °C respectively, are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), ultraviolet-visible spectrophotometer (UV-Vis), fluorescence spectrometer (FL) and the photocatalytic activity is tested by the decomposition of methyl orange dye under UV illumination. The results show that the mean grain size, surface-to-volume ratio, rms roughness and degradation efficiency of the thin films increases with increasing annealing temperature. In particular, ZnO thin film annealed at 800 °C exhibits the highest photocatalytic activity, degrading methyl orange by almost 88% in 180 min. Photocatalytic reaction mechanism of the ZnO thin films is discussed in detail, and the oxygen defects are proposed to be the active sites of the ZnO photocatalyst.     

Electrical and optical properties of Sb-doped ZnO thin films synthesized by sol–gel method

Sb-doped ZnO thin films with different values of Sb content （from 0 to 1.1 at.%） are deposited by the sol-gel dip- coating method under different sol concentrations. The effects of Sb-doping content, sol concentration, and annealing ambient on the structural, optical, and electrical properties of ZnO films are investigated. The results of the X-ray diffraction and ultraviolet-visible spectroscopy （UV-VIS） spectrophotometer indicate that each of all the films retains the wurtzite ZnO structure and possesses a preferred orientation along the c axis, with high transmittance （〉 90%） in the visible range. The Hall effect measurements show that the vacuum annealed thin films synthesized in the sol concentration of 0.75 mol/L each have an adjustable n-type electrical conductivity by varying Sb-doping density, and the photoluminescence （PL） spectra revealed that the defect emission （around 450 nm） is predominant. However, the thin films prepared by the sol with a concentration of 0.25 mol/L, despite their poor conductivity, have priority in ultraviolet emission, and the PL peak position shows first a blue-shift and then a red-shift with the increase of the Sb doping content.     

Effects of high-dose Ge ion implantation and post-implantation annealing on ZnO thin films

This paper reports that ion implantation to a dose of 1×10¹⁷ ions/cm² was performed on c-axis-orientated ZnO thin films deposited on (0001) sapphire substrates by the sol-gel technique. After ion implantation, the as-implanted ZnO films were annealed in argon ambient at different temperatures from 600-900℃. The effects of ion implantation and post-implantation annealing on the structural and optical properties of the ZnO films were investigated by x-ray diffraction (XRD), photoluminescence (PL). It was found that the intensities of (002) peak and near band edge (NBE) exitonic ultraviolet emission increased with increasing annealing temperature from 600-900℃. The defect related deep level emission (DLE) firstly increased with increasing annealing temperature from 600- 750℃, and then decreased quickly with increasing annealing temperature. The recovery of the intensities of NBE and DLE occurs at \sim 850℃ and \sim 750℃ respectively. The relative PL intensity ratio of NBE to DLE showed that the quality of ZnO films increased continuously with increasing annealing temperature from 600 - 900℃.     

退火对ZnO:Al薄膜光致发光性能的影响

 采用溶胶-凝胶工艺在石英衬底上制备ZnO:Al（AZO）薄膜,通过不同温度的退火处理,研究了退火对AZO薄膜结构和光致发光特性的影响。XRD图谱表明：所制备的薄膜具有c轴高度择优取向,随着退火温度的升高,(002)峰的强度逐渐增强,同时(002)峰的半高宽逐渐减小,表明晶粒在不断增大。未退火样品的光致发光（PL）谱由361 nm附近的紫外带边发射峰和500 nm附近的深能级发射峰组成。样品经退火后,以500 nm为中心的绿带发射逐渐减弱,而带边发射强度有所增强,并且逐渐红移到366 nm附近,与吸收边移动的测试结果相吻合。对经过不同时间退火的样品分析表明,AZO薄膜的发光特性与退火时间也有很大关系,时间过短可见波段的发射较强,但时间过长会使晶粒发生团聚,导致紫外发射峰强度减弱。     

Preparation and characterization of nano and microcrystalline ZnO thin films by PLD

Nano and microcrystalline ZnO thin films were prepared on glass substrates using pulsed laser deposition technique under a vacuum of 3 × 10⁻⁷ Torr at different laser power density. Composition analyses show that the films deposited at low laser power density have more structural defects than the film deposited at high laser power density. It confirms that the content of Zn in free-state decreased greatly at high laser power density. Atomic force microscopy analysis shows that the surface roughness of the deposited films increases with an increase in laser power density. X-ray diffraction analyses show that all the films are oriented along (0 0 2) direction independently on the laser power density applied. The structural quality increases with an increase in laser power density. It is due to the fact that the increase of laser power density leads to the enhancement of peak intensity. The increase of laser power density reduces the film transmission in the visible range of the spectra. The optical band gap value is found to be in the range from 3.42 to 3.39 eV. It shows that the optical band gap value decreases with an increase in laser power density. FTIR analysis shows that the hydrated oxide content in the deposited films decreases with an increase in laser power density.