Engineering of nearly strain-free ZnO films on Si(1 1 1) by tuning AlN buffer thickness

ZnO properties were investigated as a function of AlN buffer layer thickness (0–100 nm) in ZnO/AlN/Si(1 1 1) structures grown by metal organic vapor phase epitaxy. A significant improvement of ZnO film crystallinity by tuning AlN buffer thickness was confirmed by x-ray diffraction, topography and photoluminescence measurements. An optimal AlN buffer layer thickness of 50 nm is defined, which allows for growth of nearly strain-free ZnO films. The presence of free excitons at 10 K suggests high crystal quality for all ZnO samples grown on AlN/Si(1 1 1) templates. The intensities of neutral and ionized donor bound exciton lines are found to correlate with the in-plane and out-of-plane strain in the films, respectively.     

Magnesium incorporation efficiencies in Mg_xZn_(1-x)O films on ZnO substrates grown by metalorganic chemical vapor deposition

We investigate the magnesium(Mg) incorporation efficiencies in Mg_xZn_(1-x)O films on c-plane Zn-face ZnO substrates by using metalorganic chemical vapor deposition(MOCVD) technique. In order to deposit high quality Mg_xZn_(1-x)O films,atomically smooth epi-ready surfaces of the hydrothermal grown ZnO substrates are achieved by thermal annealing in O_2 atmosphere and characterized by atomic force microscope(AFM). The AFM, scanning electron microscope(SEM),and x-ray diffraction(XRD) studies demonstrate that the Mg_xZn_(1-x)O films each have flat surface and hexagonal wurtzite structure without phase segregation at up to Mg content of 34.4%. The effects of the growth parameters including substrate temperature, reactor pressure and Ⅵ/Ⅱ ratio on Mg content in the films are investigated by XRD analysis based on Vegard's law, and confirmed by photo-luminescence spectra and x-ray photoelectron spectroscopy as well. It is indicated that high substrate temperature, low reactor pressure, and high Ⅵ/Ⅱratio are good for obtaining high Mg content.     

Epitaxial Properties of Co-Doped ZnO Thin Films Grown by Plasma Assisted Molecular Beam Epitaxy

High quality Co-doped ZnO thin films are grown on single crystalline Al2O3（0001） and ZnO（0001） substrates by oxygen plasma assisted molecular beam epitaxy at a relatively lower substrate temperature of 450℃. The epitaxial conditions are examined with in-situ reflection high energy electron diffraction （RHEED） and ex-situ high resolution x-ray diffraction （HRXRD）. The epitaxial thin films are single crystal at film thickness smaller than 500nm and nominal concentration of Co dopant up to 20%. It is indicated that the Co cation is incorporated into the ZnO matrix as Co^2＋ substituting Zn^2＋ ions. Atomic force microscopy shows smooth surfaces with rms roughness of 1.9 nm. Room-temperature magnetization measurements reveal that the Co-doped ZnO thin films are ferromagnetic with Curie temperatures Tc above room temperature.     

Ultraviolet emission of ZnO film prepared by electrophoretic deposition

We deposited high quality ZnO film by electrophoretic deposition (EPD) using high quality ZnO powder prepared by solid-state pyrolytic reaction. X-ray photoelectron spectroscopy (XPS) and the infrared (IR) absorption spectrum clearly indicate that the ZnO phase powder has been prepared. Transmission electron microscope (TEM) imaging and x-ray diffraction (XRD) show that the average grain size of the powder is about 20nm. XRD and selected-area electron diffraction (SAED) reveal that the ZnO film has a polycrystalline hexagonal wurtzite structure. Only a strong ultraviolet emission peak at 390nm can be observed at room temperature.     

The structural and optical properties of ZnO bulk and nanocrystals under high pressure

The elastic properties of high-quality ZnO crystals and nanopowder of grain size of about 65 nm are studied for both wurtzite (low pressure) and rock-salt high pressure phases. The measured values of bulk moduli for wurtzite and rock-salt phases of bulk ZnO crystals are equal to 156±13 and 187±20 GPa, respectively, and considerably larger for ZnO nanocrystals. The phase transition begins at a pressure of about 9 GPa and it is completed at a pressure of about 13.8 GPa for bulk crystals, whereas the values of pressure at which the phase transition occurs are lower for nanocrystals. A carefull Rietveld analysis of the obtained data does not exhibit the presence of any intermediate phases between low pressure wurtzite and high pressure rock-salt phases of ZnO. The phase transition is accompanied by a strong decrease in the near-band-gap photoluminescence intensity. In addition, the pressure coefficient of the near-band-gap luminescence in ZnO nanocrystals exhibits strong deviation from the linearity observed in bulk crystals. An analysis of the results shows that defects present in the nanopowdered sample are responsible for the observed effects.     

硅衬底上Zn1-xMgxO薄膜的结构与光学性质

采用脉冲激光法（PLD）在Si衬底上沉积Zn1-xMgxO薄膜.x射线衍射(XRD)表明薄膜为c轴取向，（002）峰的半高宽仅为0.211°，且没有MgO的相偏析.透射电子显微镜可以清楚看到Zn1-xMgxO薄膜的c轴择优取向.在选区电子衍射图中可以看到Zn1-xMgxO结晶薄膜整齐的衍射斑点.室温下对Zn1-xMgxO薄膜进行了光致荧光光谱分析，发现其带边发射峰相对ZnO晶体有0.4eV的蓝移，带边发射峰与杂质发射峰的强度之比高达159.Zn1-xMgxO结晶薄膜质量良好，显示了应用于光电器件的潜力. 关键词： Zn1-xMgxO合金薄膜 硅衬底 脉冲激光沉积法 c轴取向 光致荧光光谱     

Influence of nitrogen and magnesium doping on the properties of ZnO films

Undoped ZnO and doped ZnO films were deposited on the MgO(111) substrates using oxygen plasma-assisted molecular beam expitaxy. The orientations of the grown ZnO thin film were investigated by in situ reflection high-energy electron diffraction and ex situ x-ray diffraction(XRD). The film roughness was measured by atomic force microscopy, which was correlated with the grain sizes determined by XRD. Synchrotron-based x-ray absorption spectroscopy was performed to study the doping effect on the electronic properties of the ZnO films, compared with density functional theory calculations.It is found that, nitrogen doping would hinder the growth of thin film, and generate the NOdefect, while magnesium doping promotes the quality of nitrogen-doped ZnO films, inhibiting(N_2)Oproduction and increasing nitrogen content.     

生长条件对脉冲激光沉积制备ZnO：Al薄膜光电性能的影响

本文研究了脉冲激光沉积(PLD)生长过程中, 铝掺量、氧压及衬底温度等实验参数对ZnO:Al(AZO)薄膜生长的影响, 并利用扫描电子显微镜、原子力显微镜、X射线衍射、霍尔效应、光透射光谱等实验手段对其透明导电性能进行了探讨. 变温霍尔效应和光透射测量表明, 当靶材中铝掺量大于0.5 wt%时, 所制备AZO薄膜中铝施主在80 K时已完全电离, 因Bernstein-Moss (BM) 效应其带隙变大, 均为重掺杂简并半导体. 进一步系统研究了氧压和衬底温度对AZO薄膜透明导电性能的影响, 实验发现当氧压为1 Pa, 衬底温度为200 ℃时, AZO 导电性能最好, 其霍尔迁移率为28.8 cm²/V·s, 薄膜电阻率最小可达2.7×10^-4 Ω·cm, 且在可见光范围内光透过率超过了85%. 氧压和温度的增加, 都会导致薄膜电阻率变大. 关键词： 脉冲激光沉积法 ZnO：Al薄膜 透光性 导电性     

ZnO nanorods/plates on Si substrate grown by low-temperature hydrothermal reaction

The zinc oxide (ZnO) nanorods/plates are obtained via hydrothermal method assisted by etched porous Al film on Si substrate. The products consist of nanorods with average diameter of 100 nm and nanoplates with thickness of 200-300 nm, which are uniformly distributed widely and grown perpendicularly to the substrate. The ZnO nanoplates with thickness of 150-300 nm were grown on Si substrate coated with a thin continuous Al film (without etching) in the same aqueous solution. The growth mechanism and room temperature photoluminescence (PL) properties of ZnO nanorods/plates and nanoplates were investigated. It is found that the introduction of the etched Al film plays a key role in the formation of ZnO nanorods/plates. The annealing process is favorable to enhance the UV PL emissions of the ZnO nanorods/plates.     

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。     

MOCVD法生长SAWF用ZnO/Diamond/Si多层结构

使用等离子体辅助MOCVD系统在金刚石,硅衬底上成功地制备了氧化锌多层薄膜材料,通过两步生长法对薄膜质量进行了优化。XRD测试显示优化后的样品具有c轴的择优取向生长,PL谱测试表明样品经优化后不仅深能级发射峰消失,同时紫外发射峰增强。对优化后的样品的表面测试显示出较低的表面粗糙度。比较氧化锌多层薄膜结构的声表面波频散曲线,ZnO薄膜声表面滤波器受膜厚和衬底材料的影响较大。当ZnO薄膜较薄时,在它上面的传播速度将与衬底上的传播速度接近,与其他衬底上生长的薄膜相比,以金刚石这种快声速材料为衬底的ZnO多层薄膜结构,声表面波滤波器的中心频率将提高1倍左右。     

Chemical bath-deposited ZnS thin films: Preparation and characterization

Chemical bath deposition of ZnS thin films from NH₃/SC(NH₂)₂/ZnSO₄ solutions has been studied. The effect of various process parameters on the growth and the film quality are presented. The influence on the growth rate of solution composition and the structural, optical properties of the ZnS thin films deposited by this method have been studied. The XRF analysis confirmed that volume of oxygen of the as-deposited film is very high. The XRD analysis of as-deposited films shows that the films are cubic ZnS structure. The XRD analysis of annealed films shows the annealed films are cubic ZnS and ZnO mixture structure. Those results confirmed that the as-deposited films have amorphous Zn(OH)₂. SEM studies of the ZnS thin films grown on various growth phases show that ZnS film formed in the none-film phase is discontinuous. ZnS film formed in quasi-linear phase shows a compact and a granular structure with the grain size about 100 nm. There are adsorbed particles on films formed in the saturation phase. Transmission measurement shows that an optical transmittance is about 90% when the wavelength over 500 nm. The band gap (E_g) value of the deposited film is about 3.51 eV.     

ZnO/Cu_2O异质结纳米阵列制备及光催化性能

利用湿化学法在FTO玻璃基底上制备了高度规整的ZnO纳米棒阵列(ZnO NRAs),以此为衬底,采用磁控溅射法在ZnO NRAs表面沉积Cu_2O薄膜。分别用X射线衍射仪、X射线光电子能谱、扫描电镜、光致光谱、紫外可见分光光度计和电化学工作站对样品的物相、形貌、吸收光谱、光电性能进行了表征,用甲基橙(MO)模拟有机物废水研究复合材料的光催化性能。结果表明:ZnO纳米棒为六方纤锌矿结构,其直径约为80~100 nm,长约2~3μm,棒间距约100~120 nm。立方晶系的Cu_2O颗粒直径约为100~300 nm,形成致密膜层并紧密覆盖在ZnO NRAs表面上,构成ZnO/Cu_2O异质结纳米阵列(ZnO/Cu_2O HNRAs)结构。与纯ZnO NRAs和Cu_2O相比,ZnO/Cu_2O HNRAs在可见光范围内的吸收显著增强,吸收波长向可见光方向偏移。ZnO/Cu_2O HNRAs的载流子传递界面的电荷转移速度快,有效促进了光生电子和空穴的分离。在紫外-可见光照射65 min后,ZnO/Cu_2O HNRAs的降解效率为94%,分别是纯ZnO NRAs和Cu_2O的18倍和1.7倍。     

ZnO nanowall networks grown on DiMPLA pre‐patterned thin gold films

ZnO nanowall networks grown by a high pressure pulsed laser deposition (PLD) technique on a pre‐patterned thin gold film are presented. The thin gold film on a c ‐plane oriented sapphire substrate was structured with diffraction mask projection laser ablation (DiMPLA). It is shown that only areas processed with the laser patterning technique reveal homogeneous growth of ZnO nanowall networks. Photoluminescence measurements prove the higher material quality of the pre‐patterned regions compared to the untreated ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

对硅片上自组装生长的Pentacene薄膜生长机制及其结晶相态的研究

采用热蒸发的方法在硅片衬底上自组装生长的Pentacene薄膜,薄膜在80℃温度下经2 h恒温真空热处理,通过原子力显微镜(AFM)对Pentacene薄膜表面形貌及其生长机制进行研究.结果得到,在硅片上生长的Pentacene薄膜足以台阶岛状结构生长,其岛状直径约为100 nm.且Pentacene分子以垂直于衬底的方向生长,台阶岛状结构中每个台阶的平均高度约为1.54 nnl·s-1,与Pentacene分子的沿长轴方向的长度相近.从Pentacene薄膜的XRD图谱中可以看出,薄膜在形成的过程中会因条件的不同而形成不同的结晶相,分别为薄膜相和三斜体相,且薄膜的结晶相将随着薄膜厚度的增加向三斜体相转变,其临界厚度为80和150 nm,当薄膜大于150 nm时,薄膜的三斜体相占主导地位,而当Pentacene薄膜的厚度小于80 nm时,Pentacene薄膜呈薄膜相存在.     

Pulsed laser deposition of ZnO grown on glass substrates for realizing high-performance thin-film transistors

We report characterization of ZnO thin-film transistors (TFTs) on glass substrates fabricated by pulsed laser deposition (PLD). ZnO films were characterized by X-ray diffraction (XRD), atomic force microscopy and Hall effect measurements. The XRD results showed high c-axis-oriented ZnO(0002) diffraction corresponding to the wurtzite phase. Moreover, the crystallization and the electrical properties of ZnO thin films grown at room temperature are controllable by PLD growth conditions such as oxygen gas pressure. The ZnO films are very smooth, with a root-mean-square roughness of 1 nm. From the Hall effect measurements, we have succeeded in fabricating ZnO films on glass substrates with an electron mobility of 21.7 cm²/V s. By using the ZnO thin film grown by two-step PLD and a HfO₂ high-k gate insulator, a transconductance of 24.1 mS/mm, a drain current on/off ratio of 4.4×10⁶ and a subthreshold gate swing of 0.26 V/decade were obtained for the ZnO TFT.     

具有窄光致发光谱的纳米Si晶薄膜的激光烧蚀制备

采用XeCl脉冲准分子激光器，在10Pa的Ar气环境下，烧蚀高阻单晶Si靶，分别在距靶3cm的玻璃和单晶Si衬底上制备了纳米Si薄膜. 相应的Raman谱和x射线衍射谱均证实了薄膜中纳米Si晶粒的形成. 扫描电子显微镜图像显示，所形成的薄膜呈均匀的纳米Si晶粒镶嵌结构. 相应的光致发光峰位出现在599nm，峰值半高宽为56nm，与相同参数下以He气为缓冲气体的结果相比，具有较窄的光致发光谱，并显示出谱峰蓝移现象. 关键词： 纳米Si晶粒 脉冲激光烧蚀 薄膜形貌 光致发光     

Si(001)衬底上闪锌矿ZnO的制备与分析

采用分子束外延方法在室温下于Si(001)表面上生长ZnO材料。实验发现:样品为闪锌矿和六角结构的ZnO混合多晶薄膜,其表面分布着一系列具一定取向的近似长方形的纳米台柱结构。在不同参数的高温退火后,这些梯形台柱将变小,形成梯形纳米环,或分解为较小的纳米柱及其团簇结构等。分析表明:ZnO混合多晶薄膜的形成,以及表面纳米台柱的演变,与Si(001)衬底、较低温的生长温度及热效应等因素相关联。     

The role of a ZnO buffer layer in the growth of ZnO thin film on Al2O3 substrate

A ZnO buffer layer and ZnO thin film have been deposited by the pulsed laser deposition technique at the temperatures of 200 C and 400 C, respectively. Structural, electrical and optical properties of ZnO thin films grown on sapphire (Al₂O₃) substrate with 1, 5, and 9 nm thick ZnO buffer layers were investigated. A minute shift of the (101) peak was observed which indicates that the lattice parameter was changed by varying the thickness of the buffer layer. High resolution transmission electron microscopy (TEM) was used to investigate the thickness of the ZnO buffer layer and the interface involving a thin ZnO buffer between the film and substrate. Selected area electron diffraction (SAED) patterns show high quality hexagonal ZnO thin film with 30 in-plane rotation with respect to the sapphire substrate. The use of the buffer can reduce the lattice mismatch between the ZnO thin film and sapphire substrate; therefore, the lattice constant of ZnO thin film grown on sapphire substrate became similar to that of bulk ZnO with increasing thickness of the buffer layer.     

湿法刻蚀对Si基片孔点阵及ZnO外延薄膜周期形貌的影响

利用射频等离子体辅助分子束外延法,在刻有周期性孔点阵结构的Si衬底上生长了ZnO二维周期结构薄膜,系统研究了湿法化学刻蚀对孔形点阵Si(100),Si(111)基片表面形貌的影响,以及两种初底上ZnO外延薄膜的结晶质量与周期形貌的差异.X射线衍射及扫描电子显微测试结果表明：Si (111)衬底上生长出的ZnO二维周期结构薄膜具有较好的结晶质量与较好的周期性表面形貌.该研究结果为二维周期结构的制备提供了一种新颖的方法. 关键词： ZnO 分子束外延 Si 湿法刻蚀