Synthesis Characterization And Optical And Electrical Properties Of ZnO Based Nanostructures

ZnO is a wide-band-gap semiconductor. The research on the synthesis and application of ZnO nanostructures is one of the hot topics in material science. The exploretion of ZnO based nanostructures related to group III elements on their growth, potential physical and chemical properties and device applications has important significance not only to scientific research but also to practical application, because group III elements are the best n type dopants for ZnO. The introduction of group III elements into the structure of ZnO may provide an effective way to obtain p type ZnO material by codoping with element N, or lead to the changes of microstructure and cause the formation of twinning structure or InMO3(ZnO)m (M=In, Ga; m is integer) superlattice structure. In this thesis, N-In codoped ZnO nanostructures, In/Ga doped ZnO twinning nanostructures and InMO3(ZnO)m superlattice nanostructures are prepared in a controlled chemical vapor deposition process. Systematical studies on their preparation and properties are carried out. Major attention is paid to the following aspects:The synthesis and photoluminescence properties of N-In codoped ZnO nanobelts were investigated. N-In codoped ZnO nanobelts were prepared via chemical vapor deposition method. The morphology of the products was characterized by scanning electron microscopy (SEM), and the chemical composition of the products was analyzed by energy dispersive X-ray (EDX). Compared with undoped and In doped ZnO nanostructures, the appearance of the Raman shift at279cm-1in the Raman spectrum confirms that N is introduced into In-doped ZnO nanobelts and the products are N-In codoped ZnO nanobelts. The temperature dependent PL spectra and excitation power-dependent PL spectra at9K indicate that2No-InZn acceptor complexes are formed in N-In codoped ZnO nanobelts, the energy level of2No-InZn acceptor complex should be about112meV.The synthesis and photoluminescence properties of ZnO twinning nanostructures were investigated. Two kinds of ZnO twinning nanostructures with novel morphology were prepared by chemical vapor deposition method: one is In-doped ZnO three-edged nanobelt, and the other is In/Ga doped hexagonal-disk string. These nanostructures were characterized by SEM, X-ray powder diffraction (XRD), transmission electron microscopy (TEM). Although they have different morphologies, the two kinds of nanostructures have the same microstructures. They are both wurtzite structures of ZnO. The top/bottom surfaces of their building blocks, nanobelt or nanodisk, are the (0001) crystal plane. These building blocks are connected by {0113} and {0111} twin planes along [2110] direction. The intersection angle of different building blocks is64o or116o. According to the analysis of these twinning structures, the growth mechanism of (0113) and (0111) twin structure is proposed based on the Quadra model. The photoluminescence spectra of these two ZnO twinning nanostructures both consist of a UV emission peak and a broad emission band in visible region. The emission in visible region is stronger than that in UV region. This may be related to the formation of abundant twinning structures. The research work in this part may provide an effective path for assembling one-dimensional nanostructures into well-ordered, sophisticated nanostructures, which is helpful to achieve high density integrated optoelectronic circuits.The crystal and electronic structure of In2O3(ZnO)m were investigated by first principles. New atomic arrangement rules and ground state structural model for In2O3(ZnO)m were proposed. Zigzag modulated structure is believed to exist in the structure of In2O3(ZnO)m. The angle of Zigzag modulated structure remains the same, and the periodicity of the zigzag shape is linear to the value of m. The formation energy of In2O3(ZnO)m for the zigzag model is much smaller than that in the flat boundary structure model. The transmission of electron in the structure of In2O3(ZnO)m is related to the In-5s, and Zn-4s states.The synthesis and bending mechanism of ZnO/In2O3(ZnO)m heterostructure nanobelts were investigated. ZnO/In2O3(ZnO)m (m=4,5) heterostructure nanobelts were prepared by chemical vapor deposition method. The morphology, ingredient, and microstructure of the nanobelts were characterized by SEM, EDX, and TEM. The nanobelts are bent in shape, and consist of an In2O3(ZnO)m subnanobelt and an ZnO subnanobelt. The outer subnanobelt is In2O3(ZnO)m, and the inner subnanobelt is ZnO. The two parts share the common (0001) plane. The different lattice constants for In2O3(ZnO)4and ZnO result in a lattice mismatch and introduces strain. In this case, the strain at the (0001) interface is released by the creation of mismatch dislocations and formation of the bent shape. The radius of curvature of ZnO/In2O3(ZnO)m heterostructure nanobelts is a function of their thickness.The synthesis and field emission properties of In2-xGaxO3(ZnO)m nanobelts were investigated. In2-xGaxO3(ZnO)m nanobelts were prepared by introducing element Ga into the structure of In2O3(ZnO)m. Those nanobelts were characterized by XRD, EDX, element mapping, X-ray photoelectron spectra (XPS), and HRTEM, confirming the formation of In2-xGaxO3(ZnO)3superlattice structure. The calculated XRD results enrich the JCPDS database. In XPS survey spectra, the binding energies of the Zn-2p and In-3d peaks both exhibit a positive shift in comparison to the standard values, while the binding energy of Ga-3d peak exhibits a negative shift. This could be attributed to the change of effective charge density of In2-xGaxO3(ZnO)3caused by an electron transfer from Zn and In to Ga. Field-emission measurements of In1.63Ga0.37O3(ZnO)3nanobelts were carried out, showing good field-emission performances. The turn-on electrical field is as low as4.1V/μm; and the field enhancement factor is1059. The emission current density shows a good stability for4500seconds without any current degradation or notable fluctuation.