Zn/O ratio and oxygen chemical state of nanocrystalline ZnO films grown at different temperatures

ZnO nanocrystalline films are prepared on Si substrates at different temperatures by using metal-organic chemical vapour deposition (MOCVD). It is observed that when the growth temperature is low, the stoichiometric ratio between Zn and O atoms has a large deviation from the ideal ratio of 1:1. The ZnO grains in the film have small sizes and are not well crystallized, resulting in a poor photoluminescence (PL) property. When the temperature is increased to an appropriate value, the Zn/O ratio becomes optimized, and most of Zn and O atoms are combined into Zn-O bonds. Then the film has good crystal quality and good PL property. If the temperature is fairly high, the interfacial mutual diffusion of atoms between the substrate and the epitaxial film appears, and the desorption process of the oxygen atoms is enhanced. However, it has no effect on the film property. The film still has the best crystal quality and PL property.     

氧化锌薄膜Zn/O比和发光性能的关系

用直流反应溅射在硅基片上生长具有高取向晶粒的氧化锌薄膜,在氧气、氮气、空气气氛和不同温度下进行热处理,对所得到的样品用俄歇谱(AES)仪进行元素深层分布分析,并测量光致发光光谱。研究结果表明：1．经热处理的薄膜表面全部为缺氧表面,不同深度Zn和O含量分布(Zn／O)有所不同;2．当在氧气氛中1000℃下热处理后,在薄膜的深层可产生比较明显的氧过量;而在空气中950℃下热处理后,则可产生局部氧过量;3．光致发光谱表明,薄膜中全部为锌过量时产生纯紫外发射,而具有局部氧过量的薄膜则在产生紫外发射的同时产生绿色发光,绿光和紫外的强度比则随局部氧过量增多而增大。     

Photoluminescence and lasing properties of InAs/GaAs quantum dots grown by metal-organic chemical vapour deposition

Photoluminescence （PL） and lasing properties of InAs/GaAs quantum dots （QDs） with different growth procedures prepared by metalorganic chemical vapour deposition are studied. PL measurements show that the low growth rate QD sample has a larger PL intensity and a narrower PL line width than the high growth rate sample. During rapid thermal annealing, however, the low growth rate sample shows a greater blueshift of PL peak wavelength. This is caused by the larger InAs layer thickness which results from the larger 2-3 dimensional transition critical layer thickness for the QDs in the low-growth-rate sample. A growth technique including growth interruption and in-situ annealing, named indium flush method, is used during the growth of GaAs cap layer, which can flatten the GaAs surface effectively. Though the method results in a blueshift of PL peak wavelength and a broadening of PL line width, it is essential for the fabrication of room temperature working QD lasers.     

Effects of V/III ratio on the growth of a-plane GaN films

The non-polar a-plane GaN is grown on an r-plane sapphire substrate directly without a buffer layer by metal-organic chemical vapour deposition and the effects of V/III ratio growth conditions are investigated. Atomic force microscopy results show that triangular pits are formed at a relatively high V/III ratio, while a relatively low V/III ratio can enhance the lateral growth rate along the c-axis direction. The higher V/III ratio leads to a high density of pits in comparison with the lower V/III ratio. The surface morphology is improved greatly by using a low V/III ratio of 500 and the roughness mean square of the surface is only 3.9 nm. The high resolution X-ray diffraction characterized crystal structural results show that the rocking curve full width at half maximum along the m axis decreases from 0.757° to 0.720°, while along the c axis increases from 0.220° to 0.251° with the V/III increasing from 500 μmol/min to 2000 μmol/min, which indicates that a relatively low V/III ratio is conducible to the c-axis growth of a-plane GaN.     

Effects of annealing treatment on the formation of CO2 in ZnO thin films grown by metal-organic chemical vapor deposition

Post-growth annealing was carried out on ZnO thin films grown by metal-organic chemical vapor deposition (MOCVD). The grain size of ZnO thin film increases monotonically with annealing temperature. The ZnO thin films were preferential to c-axis oriented after annealing as confirmed by X-ray diffraction (XRD) measurements. Fourier transformation infrared transmission measurements showed that ZnO films grown at low temperature contains CO₂ molecules after post-growth annealing. A two-step reaction process has been proposed to explain the formation mechanism of CO₂, which indicates the possible chemical reaction processes during the metal-organic chemical vapor deposition of ZnO films.     

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     

原子层沉积法 生长ZnO的性质与前驱体源量的关系研究

介绍了新型材料ZnO的各项性能,并采用原子层沉积方法制备新型材料ZnO. 实验中采用二乙基锌(DEZn) 和水作为生长ZnO的前驱体源, 在蓝宝石衬底上生长ZnO; 采用氮气作为载气, 生长温度为180℃. 通过改变在实验中的通入锌源的时间, 探索不同的DEZn的源的量对薄膜的成分(Zn/O)、薄膜的厚度、生长速率、晶型、 表面形貌、三维形貌以及粗糙度的影响. 关键词： 氧化锌 原子层沉积 Zn/O     

Light-induced reversible hydrophilicity of ZnO structures grown by aqueous chemical growth

ZnO wurtzite microrods and flowerlike structures were deposited on glass and ITO substrates by the aqueous chemical growth (ACG) technique at mild temperature (95 °C). Wettability studies revealed that the as-deposited structures are hydrophilic and super-hydrophilic for short and long growth times, respectively. The hydrophilic ZnO surfaces could be reversibly switched to super-hydrophilic by alternation of UV illumination and dark storage. Our results demonstrate that ACG at low temperatures can be efficiently employed to deposit transparent photosensitive ZnO structures exhibiting reversible wettability changes.     

Photoluminescence of ZnO nanostructures grown by the aqueous chemical growth technique

Zinc oxide nanostructured films were grown by the aqueous chemical growth technique using equimolar aqueous solutions of zinc nitrate and hexamethylenetetramine as precursors. Silicon(100) and glass substrates were placed in Pyrex glass bottles with polypropylene autoclavable screw caps containing the precursors described above, and heated at 95 C for several hours. X-ray diffraction 2θ/θ scans showed that the only crystallographic phase present was the hexagonal wurtzite structure. Scanning electron microscopy showed the formation of flowerlike ZnO nanostructures, consisting of hexagonal nanorods with a diameter of a few hundred nanometers. The photoluminescence spectra of the ZnO nanostructures were recorded at 18–295 K using a cw He–Cd laser (325 nm) and a pulsed laser (266 nm). The ZnO nanostructures exhibit an ultraviolet emission band centered at 3.192 eV in the vicinity of the band edge, which is attributed to the well-known excitonic transition in ZnO.     

ZnO／AlN／Si（111）薄膜的外延生长和性能研究

用常压金属化学气相沉积法(MOCVD)在Si(111)衬底上制备了马赛克结构ZnO单晶薄膜。引入低温Al N缓冲层以阻止衬底氧化、缓解热失配和晶格失配。薄膜双晶X射线衍射2θ/ω联动扫描只出现了Si(111)、ZnO(000l)及Al N(000l)的衍射峰。ZnO/Al N/Si(111)薄膜C方向晶格常量为0.5195nm,表明在面方向处于张应力状态;其对称(0002)面和斜对称(1012)面的双晶X射线衍ω摇摆曲线半峰全宽分别为460″和1105″;干涉显微镜观察其表面有微裂纹,裂纹密度为20cm-1;3μm×3μm范围的原子力显微镜均方根粗糙度为1.5nm;激光实时监测曲线表明薄膜为准二维生长,生长速率4.3μm/h。低温10K光致发光光谱观察到了薄膜的自由激子、束缚激子发射及它们的声子伴线。所有结果表明,采用金属化学气相沉积法并引入Al N为缓冲层能有效提高Si(111)衬底上ZnO薄膜的质量。     

氧分压对Mg掺杂ZnO薄膜结晶质量和光学特性的影响

利用脉冲激光沉积技术,通过改变沉积过程中的氧气压力,在蓝宝石(0001)基片上制备了一系列ZnMgO合金.通过X射线衍射、反射和透射光谱以及室温和变温荧光光谱,对薄膜的结构和光学性能进行了系统地表征,分析了工作气压对ZnMgO合金薄膜的结晶质量及光学特性的影响.研究结果表明:随着沉积环境中氧气压力的增大,ZnMgO薄膜的结晶质量下降,富氧环境下,与蓝宝石晶格平行的ZnO晶粒的出现是导致薄膜结晶质量下降的主要原因;相对于本征ZnO,不同氧气环境下沉积的ZnMgO薄膜的紫外荧光峰均出现了不同程度的蓝移.随着工 关键词： ZnO Mg掺杂 脉冲激光沉积 薄膜生长 光学特性     

The properties of GaMnN films grown by metalorganic chemical vapour deposition using Raman spectroscopy

An investigation of room-temperature Raman scattering is carried out on ferromagnetic semiconductor GaMnN films grown by metalorganic chemical vapour deposition with different Mn content values. New bands around 300 and 669 cm-1, that are not observed in undoped GaN, are found. They are assigned to disorder-activated mode and local vibration mode (LVM), respectively. After annealing, the intensity ratio between the LVM and E2 (high) mode, i.e., ILVM /IE2 (high) , increases. The LO phonon-plasmon coupled (LOPC) mode is found in GaMnN, and the frequency of the LOPC mode of GaMnN shifting toward higher side is observed with the increase in the Mn doping in GaN. The ferromagnetic character and the carrier density of our GaMnN sample are discussed.     

Relationship between the photoluminescence and conductivity of undoped ZnO thin films grown with various oxygen pressures

The pulsed laser deposition (PLD) technique is used to deposit undoped ZnO thin films on glass substrates at 150 °C with different oxygen pressures of 40, 80, 100 and 150 mTorr. X-ray diffraction (XRD) and atomic force microscopy (AFM) studies indicated that the obtained ZnO thin films were hexagonal wurtzite-type structures with strong (0 0 2) c-axis orientation. The relationship between photoluminescence and the conductivity of the ZnO thin films grown by pulsed laser deposition at various oxygen pressures was also discussed. The intensity of the deep-level-emission (DLE) and conductivity generally increased as the oxygen pressure decreased. The intensity of DLE peak was generally proportional to the conductivity. The band gap energy values, determined from transmittance spectra, were around 3.30-3.34 eV, and decreased when the oxygen pressure increased.     

Optical and electrical properties of aluminum-doped ZnO thin films grown by pulsed laser deposition

Transparent aluminum-doped zinc oxide (AZO) thin films were deposited on quartz glass substrates by pulsed laser deposition (PLD) from ablating Zn-Al metallic targets. The structural, electrical and optical properties of these films were characterized as a function of Al concentration (0-8 wt.%) in the target. Films were deposited at a low substrate temperature of 150 °C under 11 Pa of oxygen pressure. It was observed that 2 wt.% of Al in the target (or 1.37 wt.% of Al doped in the AZO film) is the optimum concentration to achieve the minimum film resistivity and strong ultraviolet emission. The presence of Al in the ZnO film changes the carrier concentration and the intrinsic defects.     

ZnO/Zn界面对纳米ZnO薄膜光学性质的影响

采用氧等离子体辅助电子束蒸发金属Zn后低温退火的方法制备纳米ZnO薄膜。利用X射线衍射(XRD)谱、拉曼(Raman)谱、X射线光电子能谱(XPS)以及光致发光(PL)谱等手段,分析了退火温度及ZnO/Zn界面对样品的结构和发光性质的影响。Raman结果表明随着退火温度的升高,界面模式(Es)振动减弱并向低波数方向移动。当退火温度为400℃时,界面振动消失,Zn全部转化成具有六方纤锌矿结构的ZnO,得到化学配比的纳米ZnO薄膜。PL谱表明,经400℃退火处理的样品紫外发射最强,发光性质最好。     

ZnS thin films grown by atomic layer deposition on GaAs and HgCdTe substrates at very low temperature

ZnS films grown on GaAs and HgCdTe substrates by atomic layer deposition (ALD) under very low temperature were investigated in this work. ZnS films were grown under several temperatures lower than 140 °C. The properties of the films were investigated with high-resolution X-ray diffraction (HRXRD), scanning electron microscope (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The results showed the ZnS films were polycrystalline. The growth rate monotonically decreased with temperature, as well as the root mean square (r.m.s) roughness measured by AFM. XPS measurement revealed the films were stoichiometric in Zn and S.     

Optically and electrically pumped random lasing from ZnO films annealed at different temperatures

We have investigated the optically and electrically pumped random lasing (RL) actions in ZnO films annealed at low and high temperatures respectively. While the optically pumped RL threshold for the ZnO film annealed at a low temperature, which features stronger light scattering and larger optical loss, is far higher than that for the ZnO film annealed at a high temperature, the electrically pumped RL threshold currents for the two ZnO films are almost the same with the electrical pumping scheme of metal-insulator-semiconductor structure. It is suggested that if the lasing region within the ZnO film is narrow enough in the case of electrical pumping, the strong light scattering can substantially alleviate the adverse effect of large optical loss on the onset of RL.     

Dynamic scaling and optical properties of Zn（S,O, OH） thin film grown by chemical bath deposition

The scaling behavior and optical properties of Zn(S, O and OH) thin films deposited on soda-lime glass substrates by chemical bath deposition method were studied by combined roughness measurements, scanning electron microscopy and optical properties measurement. From the scaling behaviour, the value of growth scaling exponent β , 0.38±0.06, was determined. This value indicated that the Zn(S, O, OH) film growth in the heterogeneous process was influenced by the surface diffusion and shadowing effect. Results of the optical properties measurements disclosed that the transmittance of the film was in the region of 70%-88% and the optical properties of the film grown for 40 min were better than those grown under other conditions. The energy band gap of the film deposited with 40 min was around 3.63 eV.     

低温缓冲层对氧化锌薄膜质量的影响

利用金属有机化学气相沉积(MOCVD)法,在Si衬底上外延生长ZnO薄膜。为了改善氧化锌薄膜的质量,首先在Si衬底上生长低温ZnO缓冲层,然后再生长高质量的ZnO薄膜。通过XRD、SEM、光致发光(PL)光谱的实验研究,发现低温ZnO缓冲层可有效降低ZnO薄膜和Si衬底之间的晶格失配以及因热膨胀系数不同引起的晶格畸变。利用低温缓冲层生长的ZnO薄膜的(002)面衍射峰的强度要比直接在Si上生长的ZnO薄膜样品的高,并且衍射峰的半高宽也由0.21°减小到0.18°,同时有低温缓冲层的样品室温下的光致发光峰也有了明显的增高。这说明利用低温缓冲层生长的ZnO薄膜的结晶质量和光学性质都得到了明显改善。     

Role of VI/II ratio on the growth of ZnO nanostructures using chemical bath deposition

In this paper the growth process and morphological evolution of ZnO nanostructures were investigated in a series of experiments using chemical bath deposition. The experimental results indicate that the morphological evolution depends on the reaction conditions, particularly on OH⁻ to Zn²⁺ ratio (which directly affects the pH). For low VI/II ratios, quasi-spherical nanoparticles of an average diameter 30 nm are obtained, whereas for larger VI/II ratios, nanorods with an average diameter less than 100 nm are produced, which indicates that by systematically controlling the VI/II ratio, it is possible to produce different shapes and sizes of ZnO nanostructures. A possible mechanism for the nanostructural change of the as-synthesized ZnO from particle to rod was elucidated based on the relative densities of H⁺ and OH⁻ in the solution.