Controlable Fabrication Of ZnO Nanorod And Manipulation Of Its Optical And Electrical Properties

Zinc oxide is an important and attractive wide band gap semiconductor due to its excellent optical and electrical properties. After having been investigated for several decades, the interest in ZnO nanostructures is fueled and accelerated by its prospects in the optoelectronic application. Obviously, the rational design and preparation of ZnO nanostructures with well controllable morphology, optoelectronic properties, and various modulations through defect and dopping are prerequisite to this end. In this context, systematical investigation and comprehensive understanding of the ZnO nanostructures on the strategies of controllable fabrication, the correlation between the optoelectronic properties and unique structure are quite necessary. In this dissertation, we focused on several interesting issues of the ZnO nanostructures, which include that, how the oxygen vacancy affects the electron and phonon interaction and modulate the near band edge (NBE) emission of ZnO nanorods, how to integrate and optimize the optical and electrical properties of ZnO nanorod through interfacial doping, and how to rationally control the axial and radial direction growth of ZnO nanorod separately and realize various advanced ZnO nanostructure. The contents of the dissertation are outlined as follows.In chapter one, we first summarize the morphologies and fabrication methods of ZnO nanostructure. Then we briefly introduce the optical, electrical properties and device application of ZnO nanostructures. Lastly, we present the aim and the main content of our work.In chapter two, we intentionally prepared a series ZnO nanorod arrays with different concentrations of oxygen vacancy through control of the growth condition. A spectral shift in the ultraviolet (UV) emission between these nanorods, as large as80meV, has been observed in the room temperature photoluminescence (PL) spectra, showing strong correlation to the Vo concentration. With the help of the variable-temperature PL, this spectral shift is clearly attributed to the different spectral contributions of the free exciton emission and its phonon replicas. Furthermore, a remarkable variation in the electron-phonon interaction strength among these samples is unambiguously revealed by the Raman spectra, which is in good consistence with the Huang-Rhys parameters obtained from the PL. We attribute this phenomenon to the suppression of the Frohlich interaction by the localized electronic states of the Vo through screening the free electrons. Additionally, from the point of view of the lattice relaxation theory, we further suggest that the ionized defect in the ZnO can also be as a decoupler to reduce the electron-phonon coupling, which may be used to understand the size and crystal surface dependent of NBE luminescence of ZnO nanostructure.In chapter three, we reported a new synthetic strategy to overcome the difficulty by introducing a native interfacial doping layer in core-shell type ZnO nanorods from a simple vapor phase re-growth procedure. Systematical characterizations imply that this interfacical doping can provide a large number of n-type carriers in the nanorod and prevent the inner exciton from breaking. This lead to maximizing ZnO integrated electrical and optical properties simultaneously with the excellent electrical (1-2orders of magnitude higher in conductivity) and optical (at least10-fold intensified NBE emission) performances with respect to the homogeneous ZnO nanorods. Moreover, this core-shell type ZnO nanorods also possess of well improved chemical stability. Based on the unique nanostructure, we contribute the above exceptional behavior to the thin two-dimensional electron gas (2DEG) like accumulation layer formed spontaneously near the core-shell interface through the interfacial doping. The2DEG can supply the high density carriers in the nanorod while sustain their mobility.In chapter four, we developed a rational and straightforward multistep growth method to design and fabricate various shaped ZnO nanostructure. We find that mild Li doping in the preparation of ZnO nanostructures can drastically alter the prior growth direction of ZnO nanorod from<0001> to<10-10>. Based on this finding, the length and diameter of the ZnO nanorods can therefore be well controlled independently by switching on/off of Li element in the preparation processing. Some nanostructures with peculiar morphology, such as nanosyringe or nanocomb, are fabricated and demonstrated successfully through the multistep growth or switching sequence.In chapter five, we presented a brief outlook for the ongoing work.