Thickness effect on the evolution of morphology and optical properties of ZnO films

N-Al co-doped ZnO films with various thicknesses were deposited on glass substrates by ultrasonic spray pyrolysis (USP). The crystalline microstructure, morphology, distribution of elements and photoluminescence properties of ZnO films were characterized by X-ray diffraction (XRD), field emission scanning microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and photoluminescence (PL) spectroscopy. The XRD and FESEM results show that with the increase of film thickness the grain size increases and the grain shape changes from regular hexagonal sheet-like to wedge-shaped, even pyramidal. The PL spectra illustrate that there is an obvious red-shift for the emission center from ultraviolet to blue region, and the intensities of defects emissions increase with the increase of thickness. In addition, the electrical properties are proved to be strongly affected by film thickness.     

Correlation between the structural and optical properties of Co doped ZnO thin films prepared at different film thickness

Cobalt doped zinc oxide (ZnO:Co) thin films were deposited on glass substrates by ultrasonic spray technique decomposition of Zinc acetate dihydrate and cobalt acetate tetrahydrate in an ethanol solution with film thickness. All films are polycrystalline with a hexagonal wurtzite-type structure with a preferential orientation according to the direction (0 0 2), with the maximum crystallite size was found of 59.42 nm at 569 nm. The average transmittance of all films is about 65–95% measured by UV–vis analyzer. The band gap energy increased from 3.08 to 3.32 eV with increasing the film thickness from 192 to 569 nm. The increase of the electrical conductivity with increases in the film thickness to maximum value of 9.27 (Ω cm)⁻¹ can be explained by the increase in carrier concentration and displacement of the electrons of the films. The correlation between the band gap and crystal structure suggests that the band gap energy of Co doped ZnO is influenced by the crystallite size and the mean strain.     

退火及超声处理对ZnO薄膜结构和发光特性的影响

 利用对向靶射频磁控溅射系统在Si（100）衬底上制备了ZnO薄膜,并对其进行了退火和超声处理。采用XRD,AFM和光致发光谱对其结构、表面形貌和性能进行了分析。结果表明：沉积态ZnO薄膜（002）择优取向稍差,尺寸较小,表面粗糙度较大。随退火温度的升高,颗粒粒径增大,样品的取向性和结晶度都明显变好,应力状态由压应力转变为张应力,粗糙度降低。超声处理缓解了薄膜中的张应力,晶粒尺寸更趋增大;用波长为280 nm的激发光激发薄膜时,沉积态薄膜无发光峰存在;随着退火温度升高,出现了一个378 nm的紫外峰和一个398 nm的紫峰;紫外峰峰值强度随退火温度升高不断增强,而紫峰的峰位随退火温度升高基本不发生变化,峰值强度增强;700 ℃退火后的薄膜经超声处理后,发光谱中出现了峰值波长为519 nm的绿色发光带。     

The relationship between refractive index-energy gap and the film thickness effect on the characteristic parameters of CdSe thin films

CdSe thin films were deposited on glass substrates using Successive Ionic Layer Adsorption and Reaction (SILAR) method at room temperature and ambient pressure. The relationship between refractive index and energy bandgap was investigated. The film thickness effect on the structural, morphological, optical and electrical properties of CdSe thin films was investigated. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies showed that all the films exhibit polycrystalline nature with hexagonal structure and are covered well with glass substrates. The crystalline and surface properties of the films improved with increasing film thickness. The optical absorption studies revealed that the films are found to be a direct allowed transition. The energy bandgap values were changed from 1.93 to 1.87 eV depending on the film thickness. The electron effective mass (m_e^?/m_o), refractive index (n), optical static and high frequency dielectric constant (ε_o, ε_∞) values were calculated by using the energy bandgap values as a function of the film thickness. The resistivity of the films changed between 10⁶ and 10² Ω-cm with increasing film thickness at room temperature.     

The structural properties of Al doped ZnO films depending on the thickness and their effect on the electrical properties

In this study, the structural and electrical properties of AZO films with different film thickness deposited by r.f. magnetron sputtering were interpreted in relation with film growth process. The result shows that the grain size increases during film growth, which is accompanied by decrease of compressive stress, indicating the enhancement of crystallinity. The relationship between grain size and compressive stress follows the same tendency for the samples regardless of deposition temperature, which implies the strong dependencies between the grain size and the compressive stress. The XPS analysis shows that the defects such as chemisorbed oxygen and segregated Al₂O₃ cluster at grain boundary are reduced with increase of film thickness or deposition temperature, leading to increase of carrier concentration and mobility. The mobility increase is accompanied by grain size increase and compressive stress reduction, indicating the influences of grain boundary and crystallinity on the mobility.     

Influence of thickness and crystalline structure on thermal and optical properties of ZnO thin films

Measurements of the temperature dependence of refractive index of ZnO thin films and thermal diffusivity using photothermal deflection technique are presented. Thin film thickness and surface homogeneity were found to be the effective parameters on optical and thermal properties of the thin films. High refractive index gradient with temperature was found for films of a nonuniform distribution and gathered in clusters, and a high predicted value for thermal diffusivity. Optical properties of the thin films revealed that films with disorder in the deposition and gathered clusters showed poor transmittance in visible region with a pronounced peak in the near IR, and also a reduction in the band gap. A detailed parametric analysis using analytical solution of one-dimensional heat equation had been performed. A discontinuity in the temperature elevation at the ZnO-glass interface was found.     

Al掺杂ZnO薄膜的厚度对其结构及磁学性能的影响

采用直流磁控共溅的方法在玻璃基底上制备了不同厚度的Al掺杂ZnO薄膜,并在真空和空气中分别退火.利用X射线衍射仪(XRD)和物理性能测量仪(PPMS)对系列薄膜的结构和磁性进行了表征.XRD结果显示:随着膜厚的增加,晶粒尺寸逐渐增大,薄膜的内应力逐渐减小.在空气退火的薄膜样品中观察到了室温的铁磁性,薄膜的饱和磁化强度M_s 随着膜厚的增加而增大,而矫顽力H_c却随着膜厚的增加而减小. 关键词： Al掺杂ZnO薄膜 薄膜厚度 应力 铁磁性     

Nitrogen oxides and ammonia sensing characteristics of SILAR deposited ZnO thin film

Pure and Sn, Ni doped ZnO thin films were deposited on glass substrates using a novel successive ionic layer adsorption and reaction (SILAR) method at room temperature. Microstructures of the deposited films were optimized by adjusting growth parameters. The variation in resistivity of the ZnO film sensors was performed with rapid photothermal processing (RPP). The effect of rapid photothermal processing was found to have an important role in ZnO based sensor sensitivity to NO₂, NH₃. While the undoped ZnO film surface exhibited higher NH₃ sensitivity than that of NO₂, an enhanced NO₂ sensitivity was noticed for the ZnO films doped with Sn and higher NH₃ sensitivity was obtained by Ni doping.     

Surface and bulk thermal annealing effects on ZnO crystals

Annealing at temperatures up to 1000 °C is shown to decrease band edge photoluminescence in bulk ZnO crystals and increase deep level-related emission. The surface roughens for anneals in the range of 600-800 °C as O is lost preferentially from the surface, but at 900 °C the morphology improves as excess Zn is also lost from the surface. Splitting of the peak in the rocking curve of the ZnO (0 0 2) plane after annealing at 900-1000 °C indicates that the substrate is a mosaic of two or more crystals oriented slightly differently from one another and we are detecting differences in orientation of some of the grains in different areas or small changes due to annealing. There was no significant change in bulk conductivity of the ZnO for anneals up to 1000 °C, suggesting that ion implantation followed by annealing may be an effective approach for doping in this.     

The influence of annealing temperature on the structure,morphologies and optical properties of ZnO nanoparticles

ZnO nanoparticles (NPs) have been successfully synthesized by the simple solution method at low temperature. The effects of annealing temperature on the structure and optical properties of ZnO NPs were investigated in detail by X-ray diffraction, transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) spectroscopy and photoluminescence (PL) measurements. As the annealing temperature was increased above 180 ^°C the particles morphology evolved from spherical to hexagonal shape, indicating that the average particle size increased from 11 nm to 87 nm. The UV-vis and PL spectra showed a red-shift from 3.62 to 3.33 eV when the annealing temperature was increased.     

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.     

Zn离子注入和退火对ZnO薄膜光学性能的影响

 利用溶胶凝胶方法在石英玻璃衬底上制备了ZnO薄膜，将能量56 keV、剂量1×10¹⁷ cm^-2的Zn离子注入到薄膜中。离子注入后，薄膜在500~900 ℃的氩气中退火，利用X射线衍射谱、光致发光谱和光吸收谱研究了离子注入和退火对ZnO薄膜结构和光学性质的影响。结果显示：衍射峰在约700 ℃退火后得到恢复；当退火温度小于600 ℃时，吸收边随着退火温度的提高发生蓝移，超过600 ℃时，吸收边随着退火温度的提高发生红移；近带边激子发光和深能级缺陷发光都随退火温度的提高而增强。     

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.     

AlN缓冲层对ZnO薄膜质量的影响

采用脉冲激光沉积法以AlN为缓冲层在Si(100)衬底上制备了ZnO薄膜,并测量了样品的XRD谱、SEM图和PL谱.结果表明,AlN缓冲层可以提高Si衬底上外延生长ZnO薄膜的晶体质量.改变缓冲层的生长温度(50～500 ℃)所制备样品的测量结果表明,较低温度下生长的AlN缓冲层有利于制备高质量的ZnO外延层薄膜,其中AlN缓冲层生长温度为100 ℃时外延生长ZnO薄膜晶体质量最好.     

Growth and characteristics of hydrogenated In-doped ZnO thin films by pulsed DC magnetron sputtering

We investigated the role of hydrogen impurities in highly oriented In-doped ZnO (IZO:H) films. The conductivity of ZnO:H films exhibit small variation despite the increase of hydrogen ratio. The small variation of the carrier concentration in IZO:H films can be explained by the reduction of the oxygen deficiency for the charge neutrality and the increase of Vzn-H bonding for partially charge compensation in the films. The additional mode at 573 cm⁻¹ is interpreted as vacancy clusters. The discrepancy between the increase of vacancy clusters (573 cm⁻¹) and small variation of carrier concentration is attributed to the different physical characteristics of the IZO:H films due to the hydrogen existence between bulk and surface. The measured FT-IR peak at 3500 cm⁻¹ exhibits typical characteristic of O-H bonding.     

Studies of structural evolution and sensing properties of ZnO nanocrystalline films

ZnO nanocrystalline films have been prepared on Si(1 0 0) substrate using direct current (D.C) magnetron sputtering technique at room temperature. The thickness of nanocrystalline films almost linearly increased with deposition duration and the sizes of crystalline grains almost kept unchanged. After deposition, thermal annealing was performed at 800 °C in atmosphere for 2 h in order to improve the qualities of ZnO thin films. Scanning electron microscope (SEM) images showed the surface roughness of the films less than 45 nm. X-ray diffraction (XRD) patterns revealed the slight evolution of the crystal structures. Raman scattering spectra confirmed the data obtained from X-ray diffraction measurements.With these ZnO nanocrystalline films, prototypic gas sensors were fabricated. Both sensitivity and response of the sensors to different gases (H₂ and CH₄) were investigated. A quick response of time, less than 1 second to CH₄ gas sensor has been achieved.     

Effects of rapid thermal annealing on structural, magnetic and optical properties of Ni-doped ZnO thin films

XPS depth profiles were used to investigate the effects of rapid thermal annealing under varying conditions on the structural, magnetic and optical properties of Ni-doped ZnO thin films. Oxidization of metallic Ni from its metallic state to two-valence oxidation state occurred in the film annealed in air at 600 °C, while reduction of Ni²⁺ from its two-valence oxidation state to metallic state occurred in the film annealed in Ar at 600 and 800 °C. In addition, there appeared to be significant diffusion of Ni from the bottom to the top surface of the film during annealing in Ar at 800 °C. Both as-deposited and annealed thin films displayed obvious room temperature ferromagnetism (RTFM) which was from metallic Ni, Ni²⁺ or both with two distinct mechanisms. Furthermore, a significant improvement in saturation magnetization (M_s) in the films was observed after annealing in air (M_s = 0.036 μ_B/Ni) or Ar (M_s = 0.033 μ_B/Ni) at 600 °C compared to that in as-deposited film (M_s = 0.017 μ_B/Ni). An even higher M_s value was observed in the film annealed in Ar at 800 °C (M_s = 0.055 μ_B/Ni) compared to that at 600 °C mainly due to the diffusion of Ni. The ultraviolet emission of the Ni-doped ZnO thin film was restored during annealing in Ar at 800 °C, which was also attributed to the diffusion of Ni.     

Influence of buffer layer thickness on the structure and optical properties of ZnO thin films

A series of ZnO thin films were deposited on ZnO buffer layers by DC reactive magnetron sputtering. The buffer layer thickness determination of microstructure and optical properties of ZnO films was investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. XRD results revealed that the stress of ZnO thin films varied with the buffer layer thickness. With the increase of buffer layer thickness, the band gap edge shifted toward longer wavelength. The near-band-edge (NBE) emission intensity of ZnO films deposited on ZnO buffer layer also varied with the increase of thickness due to the spatial confinement increasing the Coulomb interaction between electrons and holes. The PL measurement showed that the optimum thickness of the ZnO buffer layer was around 12 nm.     

退火对多晶ZnO薄膜结构与发光特性的影响

用射频反应溅射法在Si（111）衬底上制备了C轴取向的多晶ZnO薄膜，通过不同温度的退火处理，研究了退火对多晶ZnO薄膜结构和发光特性的影响.由x射线衍射得知，随退火温度的升高，晶粒逐渐变大，薄膜中压应力由大变小至出现张应力.光致发光测量发现，样品在430nm附近有一光致发光峰, 峰的强度随退火温度升高而减弱，联合样品电阻率随退火温度升高而逐渐变大的测量及能级图，推测出ZnO薄膜中的蓝光发射主要来源于锌填隙原子缺陷能级与价带顶能级间的跃迁. 关键词： ZnO薄膜 退火 光致发光 射频反应溅射     

ZnO退火条件对硫化法制备的ZnS薄膜特性的影响

采用反应磁控溅射法在玻璃和石英衬底上沉积了ZnO薄膜, 然后经过不同条件退火和在H22S气氛中硫化最终得到ZnS薄膜. 用x射线粉末衍射仪、扫描电子显微镜和UV—VIS分光光度计 对ZnS薄膜样品进行了分析. 结果表明, ZnO薄膜硫化后的晶体结构和光学性质取决于它的退 火条件. 真空和纯O2₂中退火的ZnO薄膜硫化后只是部分形成六角晶系结构的ZnS . 而在空气 和纯N2₂中退火的ZnO薄膜则全部转变为ZnS, 在可见光范围内的光透过率 关键词： ZnS薄膜 磁控溅射 ZnO硫化 太阳电池