一維奈米半導體/壓電材料在非量子局限尺寸下之光電性質與電子結構研究

Abstract

本論文在非量子局限尺寸下研究一維奈米半導體/壓電材料之光電性質及電子結構與討論其超越其本質材料的優異光電特性。 首先，由於一維奈米材料具有次波長的直徑、高的長寬比及大的介電常數，所以具有顯著的光學異向性。在此我們發現75o–85o斜向氧化鋅單晶奈米線陣列之新穎材料具有顯著的水平雙折射及優異的偏極化放光特性。其中，此水平雙折射的大小( 0.11)比起塊材氧化鋅大一個量級。這研究結果說明此新穎材料不只可以應用於被動光學元件且可以用於具有偏極化光學偵測與發光元件。 第二，由於一維奈米材料具極大的表面積與體積比且半徑接近於德拜長度，所以光電性質強烈地被表面電子結構所影響。這裡我們透過四個主題研究一維奈米材料的電子結構（尤其是表面電子結構）與其光電性質的關係：（1）利用光電子能譜配合場效電晶體量測觀測氧化鋅奈米線的表面能帶彎曲之關係; （2）利用x光吸收光譜研究摻鉺氧化鋅奈米柱陣列的電子結構與1.54 μm放光效率; (3) 透過表面鈍化加強近帶隙發光; (4) 氧化鋅奈米帶的光響應與表面及介面效應的關係。這些研究結果非常有助於一維奈米材料製作感測器與光電元件。 最後，因為氧化鋅是纖鋅礦極性半導體具有機電耦合效應，所以利用氧化鋅奈米線陣列的壓電特性來作為能量收集的研究也在論文中被討論。而鋯鈦酸鉛是傳統認知的壓電材料，故我們也研究鋯鈦酸鉛奈米線陣列的壓電特性來與氧化鋅的結果做比較。這研究有助於深入瞭解與設計奈米發電機。

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.