Synthesis and characterization of ZnO nanostructures: optoelectronic analyses and applications
Date Issued
2010
Date
2010
Author(s)
Chao, Cha-Hsin
Abstract
In this thesis, the synthesis of ZnO nanostructures via hydrothermal method is studied. The systhesis chemistry of various ZnO structures and its material and optoelectronic characterization are reviewed and investigated. Field-emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) spectroscopy are performed to examine the properties of ZnO. Applications of ZnO nanorod arrays have been demonstrated to enhance the light extraction efficiency of light-emitting diodes (LEDs). The content of the thesis can be mainly divided into four part as follows.
1. Controlled-growth of ZnO nanostructures
The experimental techniques of controlled-growth of ZnO nanostructrures used in this dissertation and the underlying growth mechanisms are described. The effect of growth parameters on the formation of ZnO nanorod arrays is elucidated with detailed analysis from our experimental results. The scale and morphology of ZnO nanorod arrays grown on the sol-gel-derived film are controlled with a wide size range from 50 nm to 300 nm in diameter. With applying a template to limit the growth of ZnO rods, the diameters of ZnO rod arrays grown with various solution concentrations can be controlled in the range from 50 nm up to 1400 nm.
2. Hetero-growth of ZnO nanostructures
The heteroepitaxy of ZnO is accomplished on various substrates by hydrothermal method. The results show that the grown ZnO micro/nanostructures and thin films have a good epitaxial quality on GaN substraets. In addition, the differences in morphologies of ZnO rod arrays grown with various diameters of polymer apertures are discussed. The controlled diameters of rods with various solution concentrations and geometry of template are in the range from 530 nm up to 3.5 μm.
3. Enhanced light extractions efficiency of LEDs by ZnO nanorods
The effect of the ZnO rod length on the output light intensity of GaN-based LEDs is investigated. It is firstly found that the EL intensity of GaN-based with ZnO nanorod arrays is varied periodically with the rod length. The oscillation as a function of rod length can be explained as the interference of light emission between interfaces of nanorods, resulting in a modulation of light extraction efficiency of the devices.
4. Enhanced light extractions efficiency of LEDs by GaN nanorods
In addition, the effect of the geometry of GaN rod arrays on the output power of GaN LEDs is studied. It is found that the output power of GaN LEDs with GaN rod arrays is varied with the length and density of rods, which is analogous to the previous results. The Bruggemann effective medium approximation and the Fabry-Perot resonance also work well for GaN rod arrays on GaN LEDs.
Subjects
ZnO
nanorod
hydrothermal method
e-beam lithography
GaN
light-emitting diodes
light extraction efficienty
Fabry-Perot resonance
Type
thesis
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