Fabrication And Properties Of Transition Element-doped ZnO Thin Films

1D ZnO nano-structures are widely used in transparent electrodes, nonvolatile memory,solar cell, UV-light emitter and diluted magnetic semiconductor (DMS) due to their largeband gap and surface area. The change in optical, electrical, and magnetic properties occursvia adjusting morphology of ZnO nano-structure and doping by transition metal elements,therefore, both accurate control of size, shape and structure of ZnO and ions doping areextensively investigated.In this paper, Ni2+doped ZnO array films are fabricated by wet-chemical methods(including hydrothermal method and chemical solution deposition). The crystalline phases,morphologies, composition, microstructures, optical and electrical properties of theas-prepared array films are characterized by XRD, SEM, EDS, Raman spectra, PL spectra andfield emission measurement. In addition, NiO/ZnO hybrid nano structures are also fabricatedby the twice hydrothermal processes. The main contents in this paper are as follows:(1) Ni2+doped ZnO array films are synthesized by a hydrothermal method, and the effectof Ni2+doping concentration, ethanol and duration time on the crystalline phase, morphology,spectral and electrical resistive switching properties of ZnO films is investigated. The resultsindicate that Ni2+ions are soluble in the ZnO lattice within limit. Doping within a certainamount of Ni2+would not change phase composition of ZnO, however, in the presence ofmore Ni2+, the change in growth behavior of ZnO nanorods occurs, and hexagonal structure ofZnO nanorods is further destroyed. A suitable concentration of Ni2+, helps to improve thequality of crystallization decrease the structural defects. The ratio of the UV emission to thegreen emission increases and the reset voltage of thin film device decreases with increasingNi content for Ni doped ZnO nanorods within a certain range.(2) Nickel doped ZnO array films are synthesized using chemical solution deposition(CSD) method. The effect of Ni2+ions, NaOH concentrations and operating temperatures onZnO nanorod arrays is investigated, and the possible growth mechanism is discussed. Theresults show that Ni2+ions are soluble in the ZnO lattice with a low solid solubility. A moderate amount of Ni2+would be beneficial to the enhancement of ZnO crystal quality,however, it would introduce more donor defects and further inhibit the epitaxial growth ofZnO rods at a large doping amount. The morphology and size of ZnO nanorods are stronglydependent on the concentration of NaOH, and the best crystalline and longest ZnO nanorodarrays are obtained at a NaOH concentration of0.3M.(3) The increase of duration time of the second hydrothermal process has little effect onthe formation of NiO/ZnO, but the thickness of NiO on the surface of ZnO films increases.Lateral growth of ZnO nanorods is inhibited and a wiring harness-like structure is obtained byintroducing NH4OH in the Zn(NO3)2/HMT solution.