Optoelectronic Properties and Electronic Structures of One-dimensional Semiconducting/Piezoelectric Nanostructures with Sizes beyond the Quantum Confinement Regime

In this thesis, we studied optoelectronic properties and electronic structures of one-dimensional (1-D) semiconducting/piezoelectric nanostructures with sizes beyond the quantum confinement regime and discussed their superior optoelectronic/photonic features as compared to their thin film of bulk counterpart.
First of all, since 1-D nanostructures have subwavelength diameters and large aspect ratios, which combined with the high permittivity of semiconductors lead to a strong optical anisotropy, we report a novel optically anisotropic metamaterial based on single crystalline ZnO nanowire arrays (NWAs) with highly oblique angles (75o–85o), exhibiting giant in-plane birefringence and optical polarization degree in photoluminescence emission. The in-plane birefringence ( 0.11) of oblique-aligned ZnO NWAs is almost one order of magnitude higher than that of ZnO bulk. The oblique-aligned NWAs not only allow important technological applications in passive photonic components but also benefit the development of the optoelectronic devices in polarized light sensing and emission.
Second, in 1-D nanostructures, with large surface-to-volume ratios and Debye lengths comparable to their diameters, their electronic and optoelectronic properties are strongly affected by the electronic structures at their surfaces. Here we systematically and in-depth investigated the correlation between electronic structures (especially at the surface) of 1-D (Er-doped) ZnO nanostrucrures and their optoelectronic properties through the following four subjects: (1) in situ probing the surface band bending (SBB) of the ZnO NWs using photoelectron spectroscopy in conjunction with the field-effect transistor measurements; (2) correlation between electronic structures of Er-Doped ZnO nanorod arrays and efficiency of 1.54 μm emission by studied by X-ray absorption spectroscopy; (3) enhanced near-band-edge emission of ZnO nanorods via the surface passivation; (4) correlation between photoresponse of ZnO nanobelts and the surface/interface effects. These studies are greatly beneficial for the 1-D nanostructure based device design of sensor and optoelectronic applications.
Finally, since ZnO is the wurtzite polar semiconductor and has the electromechanical coupling effect, piezoelectric characteristics of well-aligned ZnO NWAs were investigated for energy-harvesting nanodevices via its piezoelectricity. Besides, lead zirconate titanate [PbZr1−xTixO3 (PZT)] is a typical piezoelectric material, so the PbZr02Ti0.8O3 NWAs were also studied. This study is useful for optimizing the performance for nanogenerator applications.