【作者】 韩祥云；

【导师】 高义华；

【作者基本信息】 华中科技大学 ， 凝聚态物理， 2011， 博士

【摘要】 ZnO低维纳米材料是一种重要的功能材料,有许多优良的性能,在化工、电子、微纳器件等领域有广泛的用途。其中,一维ZnO纳米线阵列是一种特殊结构和优异物化性能的纳米材料。有序纳米线结构将会更大地发挥ZnO纳米线的优异特性,是新型高性能纳米材料与器件研究的重要物质基础。而非极性面的ZnO薄膜在光电器件、表面声波、压电以及紫外光调制器等器件方面,同样有着重要应用价值。其纤锌矿结构会导致在极性轴[0001]方向具有很强的自发极化和压电极化效应。解决此问题最根本方法是生长非极性面的薄膜,即薄膜的生长方向垂直于[0001]方向。本论文主要围绕ZnO纳米线阵列结构的可控制备及其物性研究,和非极性ZnO薄膜的PLD生长与表征来开展,同时对非极性GaN薄膜的MOCVD生长及表征进行了研究,获得一些有意义的研究结果。其主要研究内容和结果如下:（1）采用气相法,在GaN衬底上制备了一维ZnO纳米结构,重点研究了反应物总量、催化剂厚度、沉积温度和管内真空度对纳米线阵列的形貌、直径、长度、密度、取向性的影响,得到了最佳的生长工艺参数。在靠近反应区合适的位置,管内1000²500 Pa的稳定压强下,制备出大面积形貌优良、尺寸均匀、整齐排列的纳米线阵列。从光学角度出发,阐述了纳米线的形貌、有序排列与其发光性能、声子振动特性、紫外光探测响应性能和表面润湿性之间的关系。（2）采用水热法,在低温95℃,不同导电衬底（ITO、FTO、Pt）上制备出了高取向、大面积、均匀的ZnO纳米线阵列。研究了生长时间和反应物浓度对阵列的影响。在此基础上,采用两步法构建了NiO/ZnO纳米结构阵列,和光刻胶旋涂的ZnO纳米阵列结构,重点对其出现的电阻开关效应进行了分析和讨论。通过对I-V结果线性拟合分析,得出在高低阻态不同偏压下其导电机制并不相同,这主要是由界面效应引起的。（3）采用MOCVD外延法,在r面蓝宝石衬底上生长了系列的非极性a面GaN薄膜。分析了不同生长工艺(Al_xGa_1-xN缓冲层、原位生长SiNx插入层)对本征GaN外延层生长质量的影响,取得了较好的结果。采用飞秒激光Z扫描方法,探究了非极性GaN薄膜的三阶非线性光学性质,发现了晶体对称性降低引起三阶非线性吸收系数和三阶非线性折射率具有面内各向异性。（4）利用脉冲激光沉积的方法,采用a-GaN模板作为衬底,探究非极性面ZnO薄膜的生长特性。研究不同生长温度对ZnO薄膜的晶体质量、表面形貌以及光学性质等性能的影响。通过优化成膜温度,在600℃制备出高质量a面的ZnO薄膜,其双晶衍射的半峰宽最小为0.4°,室温PL发光峰强度I_UV/I_DLE的比值高达18.5。通过对称和非对称衍射倒异空间分布图分析了倒格点的宽化机理,并得出a面ZnO膜面内具有张应变,面内两个正交方向上应变的大小分别是+0.335%和+0.055%。低温85 K下禁带边发射峰主要是由3.351 eV的中性施主束缚激子发光和3.315 eV的自由电子-束缚激子跃迁发射占主导地位。更多还原

【Abstract】 It is well known that nanoscale material ZnO is an important multifunctional material, which have many excellent properties and potential value in the chemical, electronics, micro-nano devices and other fields. Especially, ZnO nanowire arrays are the nanomaterials with special structure and excellent physical and chemical properties. The ordered nanowire structure arrays is an important material foundation for some novel high-performance nanodevices, which will develop the attractive properties of ZnO nanowire much more. Nonpolar ZnO films have an practical applications in the fields of optoelectronic, surface acoustic wave, piezoelectric, and ultraviolet light modulators and other devices. The wurtzite structure of ZnO andⅢ-nitrides leads to build-in electric fields along the [0001] direction due to strong polarization and piezoelectric polarization. The only way to solve this problem is to grow nonpolar-oriented film, where [0001] axis of the film lies down in the growth plane.In this work, we mainly focused on the ZnO nanomaterials research including controlled synthesis and properties of ZnO nanowire arrays structure, PLD growth and characterization of nonpolar ZnO films. In addition, we carried out the growth of nonpolar GaN films. The main content and innovation results are as follows:（1） Using vapor transport method, one dimensional ZnO nanostructrues were synthesied on the GaN substrates. The effects of total amount of reaction, thickness of Au catalyst, deposition temperature and the chamber vacauum on the morphology, diameter, length, density, orientation of the nanowire arrays have been investigated thoroughly. Under the optimizing reaction conditions, large area, well aligned of ZnO nanowire arrays with uniform size have been achieved successfully, with the chamber of 1000 2500 Pa steady pressure. From the optical point of view, we described the relationship between the morphology, orientation of the nanowires with their luminescent properties, the phonon vibrational features, performance of UV detection response, as well as surface wettability.（2） The highly oriented, uniform ZnO nanowire arrays with large area were synthesized at 95℃on different conductive substrates （ITO、FTO、Pt） by a low temperature hydrothermal method. The control of dimension and density of the ZnO nanowire arrays were investigated under different growth time and concentration of nutrient solution. Based on it, NiO/ZnO nanostructure arrays and ZnO nanoarrays spin-coating by photoresist were constructed by two-step methods. The resistive switching behaviors were observed in these two devices. Fitting of the current-voltage curves at forward bias at high resistive state and low resistive state revealed the different transport modes, which was presumably by the interfacial effect.（3） We have comparatively investigated the effects of the GaN, AlGaN, and AlN low-temperature buffer layers, as well as in situ SiNx layer on the crystal quality of a-plane GaN thin films grown on r-plane sapphire substrates. Moreover, we report the nonlinearity of nonpolar a-plane GaN by using Z-scan techniques with femtosecond laser pulses at 800 nm. The in-plane anisotropy of nonlinear refraction and absorption index in a-plane GaN film is experimentally investigated, which is a result of the reduced in-plane crystal symmetry.（4） Nonpolar a-plane ZnO films were deposited for the first time on nearly lattice-matched a-plane GaN templates by the pulsed laser deposition method. The effects of deposition temperature on the growth mode, crystal quality, surface morphology and optical properties of a-plane ZnO films have been investigated thoroughly. Through optimizing the reaction conditions, high quality of ZnO film was obtained successfully at depositon temperature of 600°C. The FWHM value of the X-ray rocking curve for ZnO a-plane was about 0.4°. Strong near band edge emission and very weak deep-level with I _UV/I_DLE=18.5 was observed in the PL spectrum at room temperature. The symmetric and asymmetric reciprocal space mappings revealed the broadening effects of the reciprocal lattice points and the residual biaxial in-plane tensile strain of a-plane ZnO to be 0.335% and 0.055% along two orthogonal directions. Photoluminescence spectrum at 85K was dominated by neutral donor-bound excitons and free-electron-to-bound emissions.更多还原