Slow-rise and fast-drop current feature of ultraviolet response spectra for ZnO-nanowire film modulated by water molecules

This study describes the fabrication of ZnO-nanowire films by electro-chemical anodization of Zn foil. The ZnO films are characterized by field emission scanning electron microscopy, X-ray diffraction patterns, and transmission electron microscopy, respectively. The ultraviolet (UV) photo-response properties of the surface-contacted ZnO film are studied through the current evolution processes under different relative humidities. Unlike the usually observed current spectra of the ZnO films, the drop time is shorter than the rise time. The photo-conductivity gain G and the response time τ are both increased with the increase of the applied bias. The photo-conductivity gain G is lowered with the increase of the environmental humidity, while the response time τ is increased. These results can be explained by considering three different surface processes: 1) the electron-hole (e-p) pair generation by the UV light illumination, 2) the following surface O₂^- species desorption, and 3) the photo-catalytic hydrolysis of water molecules adsorbed on the ZnO surface. The slow-rise and fast-drop current feature is suggested to originate from the sponge-like structure of the ZnO nanowires.     

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.     

氧气后处理对氧化锌薄膜紫外发射性质的影响

为了提高ZnO光发射效率和制备p型ZnO,对热处理的氧分压对薄膜的结构、形貌、光致光发射和ZnO/Si异质结的Ⅰ-Ⅴ特性的影响进行了研究.用直流反应溅射法在p型硅衬底上生长ZnO薄膜形成n-ZnO/P-Si异质结.在1000℃下用不同比例的氧和氨热处理,我们发现,在纯氮气中得到的样品有强的紫外发射(390nm),随氧气比例增大,紫外增强,同时绿光也产生并随之增强.但过大的氧分压反而产生多的受主缺陷,使越来越多的激发能量转移到发射能量低的绿光中心,从而使紫外减弱.在纯氧和无氧条件下热处理的俄歇谱表明纯氧下氧过量,而无氧下锌大大过量.ZnO/p-Si异质结的Ⅰ-Ⅴ特性表明,无氧热处理表现为典型的n-ZnO/p-Si异质结;而在纯氧气氛中处理后所得Ⅰ-Ⅴ曲线反向,这表明在高氧压下受主缺陷的产生,表明ZnO薄膜有可能由于高氧压热处理由n型转为p型.     

ZnO：V薄膜后退火处理前后的微结构与发光特性

利用溶胶-凝胶(Sol-gel)法在单晶硅(100)衬底上分别制备了ZnO:V薄膜和纯ZnO薄膜。为进一步研究后退火对ZnO:V薄膜结构和发光性质的影响,在两段式快速退火后又在800℃下进行了后退火处理。X射线衍射的结果表明:后退火处理前,钒(V)的掺入使ZnO结晶质量变差,而800℃退火处理后,从ZnO的衍射峰中可以看出,相对于无V杂样品其结晶质量变好。扫描电子显微镜形貌图中可以看出制备的样品薄膜颗粒大小均匀,薄膜致密度较高。光致发光(PL)谱的研究表明:ZnO:V薄膜在800℃退火处理后,紫外和绿带发光峰均增强,但紫外发光峰增强得更多;与同样条件下制备的纯ZnO薄膜的PL谱比较,发现V掺杂后样品的紫外激子复合发光峰的强度明显增强且峰位发生蓝移,而缺陷引起的绿带发光峰的强度降低。     

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.      

PEDOT:PSS Schottky contacts on annealed ZnO films

Polycrystalline ZnO and ITO films on SiO₂ substrates are prepared by radio frequency (RF) reactive magnetron sputtering. Schottky contacts are fabricated on ZnO films by spin coating with a high conducting polymer, poly(3, 4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) as the metal electrodes. The current-voltage measurements for samples on unannealed ZnO films exhibit rectifying behaviours with a barrier height of 0.72 eV (n=1.93). The current for the sample is improved by two orders of magnitude at 1 V after annealing ZnO film at 850 ℃, whose barrier height is 0.75 eV with an ideality factor of 1.12. X-ray diffraction, atomic force microscopy and scanning electron microscopy are used to study the properties of the PEDOT:PSS/ZnO/ITO/SiO₂. The results are useful for applications such as metal-semiconductor field-effect transistors and UV photodetectors.     

Effects of post-annealing on the structural and nanomechanical properties of Ga-doped ZnO thin films deposited on glass substrate by rf-magnetron sputtering

In this study, the effects of post-annealing on the structure, surface morphology and nanomechanical properties of ZnO thin films doped with a nominal concentration of 3 at.% Ga (ZnO:Ga) are investigated using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) and nanoindentation techniques. The ZnO:Ga thin films were deposited on the glass substrates at room temperature by radio frequency magnetron sputtering. Results revealed that the as-deposited ZnO:Ga thin films were polycrystalline albeit the low deposition temperature. Post-annealing carried out at 300, 400 and 500 °C, respectively, has resulted in progressive increase in both the average grain size and the surface roughness of the ZnO:Ga thin film, in addition to the improved thin films crystallinity. Moreover, the hardness and Young's modulus of ZnO:Ga thin films are measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option. The hardness and Young's modulus of ZnO:Ga thin films increased as the annealing temperature increased from 300 to 500 °C, with the best results being obtained at 500 °C.     

Growth and characterization of pulsed laser deposited ZnO thin films

One of the most important and promising materials from metal oxides is ZnO with specific properties for near UV emission and absorption optical devices. The properties of ZnO thin films strongly depend on the deposition method. Among them, pulsed laser deposition (PLD) plays an important role for preparing various kinds of ZnO films, e.g. doped, undoped, monocrystalline, and polycrystalline. Different approaches — ablation of sintered ZnO pellets or pure metallic Zn as target material are described. This contribution is comparing properties of ZnO thin films deposited from pure Zn target in oxygen atmosphere and those deposited from sintered ZnO target. There is a close connection between final thin film properties and PLD conditions. The surface properties of differently grown ZnO thin films are measured by secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Furthermore, different approaches — ablation of sintered ZnO pellet or pure metallic Zn as target materials are described. The main results characterize typical properties of ZnO films versus technological parameters are presented. Presented at 5-th International Conference Solid State Surfaces and Interfaces, November 19–24, 2006, Smolenice Castle, Slovakia     

一维纳米氧化锌自驱动紫外探测器的构建与性能研究

本文通过化学气相沉积法制备了ZnO纳米材料, 利用扫描电镜、光致发光谱、X衍射光谱及拉曼光谱等方法对制备的材料进行了表征. 基于制备的单根ZnO线分别构建了三种不同结构的紫外探测器件: Ag-ZnO-Ag肖特基型、PEDOT:PSS/n-ZnO结型和p-Si/n-ZnO结型紫外探测器, 并对器件的性能进行了研究. 结果表明: 三种不同结构的器件都表现出良好的整流特性, 对紫外线均有明显的光响应; 在零偏压下, 都有明显的自驱动特性. 三种器件中, p-Si/n-ZnO型紫外探测器性能最为优异: 在零偏压下, 暗电流约在1.2×10^-3 nA, 光电流在5.4 nA左右, 光暗电流比为4.5×10³, 上升和下降时间分别为0.7 s和1 s. 通过三类器件性能比较, 表明无机p-Si更适合与ZnO构建pn结型自驱动紫外探测器.     

Effect of temperature on pulsed laser deposition of ZnO films

ZnO thin films have been deposited on Si(1 1 1) substrates at different substrate temperature by pulsed laser deposition (PLD) of ZnO target in oxygen atmosphere. An Nd:YAG pulsed laser with a wavelength of 1064 nm was used as laser source. The influences of the deposition temperature on the thickness, crystallinity, surface morphology and optical properties of ZnO films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), selected area electron diffraction (SAED), photoluminescence (PL) spectrum and infrared spectrum. The results show that in our experimental conditions, the ZnO thin films deposited at 400 °C have the best surface morphology and crystalline quality. And the PL spectrum with the strongest ultraviolet (UV) peak and blue peak is observed in this condition.     

LiGaO2衬底上ZnO外延膜的结构与光学特性

采用磁控溅射法在(001),(100)及(010)LiGaO2衬底上制备了ZnO薄膜,通过X射线衍射(XRD)、原子力显微镜(AFM)、透过光谱以及光致发光谱(PL)对薄膜的结构、形貌及光学性质进行了表征.结果表明LiGaO2衬底不同晶面上制备的ZnO薄膜具有不同的择优取向,在(001)、(100)及(010)LiGaO2上分别获得了[001]、[1100]及[1120]取向的ZnO薄膜;不同取向的ZnO薄膜表面形貌差异较大;薄膜在可见光波段具有较高的透过率;在ZnO薄膜的光致发光谱中只观察到了位于378 nm的紫外发射峰,而深能级发射几乎观察不到,(1100)取向的薄膜紫外发射峰强度最大,半高宽也最小,薄膜光致发光件质的差异丰要和晶粒尺寸有关.     

热处理对ZnO:Zn荧光薄膜结晶性能的影响

用热处理方法对电子束蒸发制备的ZnO:Zn荧光薄膜分别进行400,600℃退火处理。采用X射线衍射、X射线光电子能谱、扫描电子显微镜、光致发光光谱等方法,表征了ZnO:Zn荧光薄膜的结构、成分、形貌、发光性能。在ZnO:Zn荧光薄膜的X射线衍射谱和扫描电子显微镜照片中,可以看出经退火处理后结晶状况大大改善,多晶结构趋于规则,晶粒更加均匀且膜层结构更加致密。在ZnO:Zn荧光薄膜的光致发光谱中,检测到490nm处发光峰,认为一价氧空位(V_O)充当发光中心,且薄膜的光致发光强度受热处理温度的影响很大。实验表明随着退火温度的升高,薄膜的结晶程度提高,弥补了薄膜晶体表面的表面缺陷,薄膜的发光性能不断提高。     

Rapid thermal annealing effects on the structural and optical properties of Na–N codoped ZnO films

Polycrystalline ZnO thin films codoped with Na and N were obtained by chemical bath deposition. The structural characteristic and the optical properties of the rapid thermal annealed ZnO:(Na,N) films were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer (EDS), Raman spectrum and room-temperature photoluminescence. After RTA treatment, the XRD spectra showed a continuous decrease of the full- width at half-maximum (FWHM) of the (0 0 2) diffraction peak of the ZnO:(Na,N) film. The Raman spectra revealed that the intensity of the mode around 582 cm⁻¹ increased with the increase of the RTA temperature. The PL spectra showed different trends in the UV luminescence of ZnO:(Na,N) films after RTA treatments.     

Structural and photoluminescence characteristics of ZnO films by room temperature sputtering and rapid thermal annealing process

ZnO thin films deposited on SiO₂/Si substrates at room temperature by sputtering technology were annealed with a rapid thermal annealing process at various temperatures from 200 °C to 900 °C. The physical and optical properties of the ZnO films were investigated by X-ray diffraction, scanning electron microscopy and room-temperature photoluminescence (PL). The surface structures of the thin films showed great variations with increased annealing temperature. The PL spectrum illustrated that a stronger UV emission intensity appeared at an annealing temperature of 500 °C. On the other hand, visible-light emission could be obtained when the ZnO films were annealed above 500 °C and reached a maximum intensity at 900 °C. The possible mechanisms for visible-light emission are discussed. PACS 81.15.Cd; 81.40.Ef; 78.55.-m; 78.55.Et     

两步化学沉积法制备ZnO薄膜及其场发射特性

在低温常压条件下,以ITO玻璃为衬底,采用电化学法与湿化学法结合的两步化学沉积法制备了团簇状ZnO薄膜。利用XRD,SEM分析了薄膜结构和表面形貌,并采用二极管结构在高真空条件下对薄膜进行了场发射性能测试。稳定发射后,开启电场为3.0 V/μm。当电场为5.8 V/μm时,电流密度为583.3 μA/cm²。研究表明:两步化学沉积法低温制备ZnO薄膜是可行的,且该薄膜具有良好的场发射性能。     

Nanostructure and optical properties of M doped ZnO (M=Ni, Mn) thin films prepared by sol-gel process

The transparent thin films of undoped, Mn-doped, and Ni-doped zinc oxide (ZnO) have been deposited on glass substrates via sol-gel technique using zinc acetate dehydrate, nickel chloride, and manganese chloride as precursors. The structural properties and morphologies of the deposited undoped and doped ZnO thin films have been investigated. X-ray diffraction (XRD) spectra, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to examine the morphology and microstructure of the thin films. Optical properties of the thin films were determined by photoluminescence (PL) and UV/vis spectroscopy. The analyzed results indicate that the obtained films are of good crystal quality and have smooth surfaces, which have a pure hexagonal wurtzite ZnO structure without any Mn or Ni related phases. The band gap energy was estimated by Tauc's method and found to be 3.28, 3.26, and 3.34 eV for ZnO, Ni-doped ZnO, and Mn-doped ZnO thin films at room temperature, respectively. Room temperature photoluminescence is observed for the ZnO, Ni-doped ZnO, and Mn-doped ZnO thin films.     

退火温度对ZnO薄膜结构和发光特性的影响

采用反应射频磁控溅射法在 Si(100)基片上制备了高c轴择优取向的ZnO薄膜，研究了退火温度对ZnO薄膜的晶粒尺度、应力状态、成分和发光光谱的影响，探讨了ZnO薄膜的紫外发光光谱和可见发光光谱与薄膜的微观状态之间的关系.研究结果显示,在600—1000℃退火温度范围内，退火对薄膜的织构取向的影响较小，但薄膜的应力状态和成分有比较明显的变化.室温下光致发光光谱分析发现，薄膜的近紫外光谱特征与薄膜的晶粒尺度和缺陷状态之间存在着明显的对应关系；而近紫外光谱随退火温度升高所呈现的整体峰位红移是各激子峰相对比例变 关键词： ZnO薄膜 退火 光致发光 射频反应磁控溅射 可见光发射     

溶胶-凝胶法制备氧化锌薄膜的压电行为

"采用溶胶-凝胶技术在单晶硅Si(111)上制备了ZnO压电薄膜,并以扫描电镜、X射线衍射仪(XRD)和原子力显微镜(AFM)进行了表征．XRD衍射实验表明ZnO薄膜随着膜厚的增大,其(002)取向逐渐增强;AFM研究了薄膜的表面形貌、粗糙度与晶粒大小的结果表明,ZnO压电薄膜的粗糙度与晶粒寸随着薄膜厚度的增大而减小．粗糙度为2.188~0.914 nm．利用PFM研究压电系数,发现随着薄膜厚度的增加,(002)生长方向增强,压电系数逐渐增大;当力参数小于薄膜的表面粗糙度时,压电系数测量不准确且在较大幅度     

微流控技术制备ZnO纳米线阵列及其气敏特性

利用微流控技术在微通道中制备了Zn O纳米线阵列,通过X射线衍射和扫描电子显微镜分别对纳米线的物相和表面形貌进行了表征.结果发现,合成的Zn O纳米线具有良好的c轴择优取向性和结晶度.同时,对Zn O纳米线阵列在丙酮、甲醇和乙醇气体中的气敏特性进行了研究,测试结果表明:在最佳工作温度(475?C)下,纳米线阵列对200 ppm(1 ppm=10-6)丙酮气体的最大灵敏度可达8.26,响应恢复时间分别为9和5 s;通过与传统水热法制备的Zn O纳米线的气敏性能相比较发现,基于微流控技术制备的纳米线阵列具有更高的灵敏度和更快的响应恢复速度.最后,从材料表面氧气分子得失电子的角度对Zn O纳米线气敏机理进行了讨论.     

Ultrasonic induced photoluminescence decay in sonochemically obtained cauliflower-like ZnO nanostructures with surface 1D nanoarrays

Cauliflower-like ZnO nanostructures with average crystallite size of about 55 nm which have surface one dimensional (1D) nanoarrays with 10 nm diameter were successfully fabricated through a simple sonochemical route. X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and room temperature photoluminescence (PL) characterizations were performed to investigate the morphological and structural properties of the obtained nanostructures. It has been shown that the synthesized cauliflower-like ZnO nanostructures irradiated UV luminescence and a green peak in visible band. Ultrasonic post-treatment of the particles for about 2 h increased the density of surface defects resulted in an increase in the green emission intensity.