The Preparation And Property Studies Of ZnO Nanowire Arrays And Nonpolar Films

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.