氧化鋅奈米線光電流特性之研究

本論文討論了氧化鋅奈米線的光電流效應及其機制，並利用實驗之結果提出方法，有效地提高奈米線紫外光感測器的效能並討論其結果。首先，論文中利用製備單根氧化鋅奈米線的光感測器研究表面效應對於光激發之載子複合行為的影響。結果顯示，由於表面效應的主宰，未照光時完全空乏的奈米線將表現出增強型的場效電晶體行為以及空間電荷限制電流的傳輸行為。而在照光後的光電流回復階段，光電流隨時間衰減的行為被發現和照射光強度及奈米線本身直徑有所關連，進而顯示光激發載子的複合是由表面能帶彎曲行為所主導。相關的模型及實驗結果之解釋將在第三章中詳細討論。第二，論文中利用奈米金粒子對於氧化鋅奈米線的表面修飾方法，證明其所產生的局部蕭基接面效應將可有效提升奈米線光偵測器之光電流以及光電增益的表現。由於局部蕭基接面效應所造成的空間電荷分佈改變，光激發之電子電洞對更易產生空間之分離，進而造成光電流之增強。另外發現，由於奈米金粒子修飾的奈米線對於照光時所造成的表面能帶彎曲變化相對較小，使得光偵測器在高強度紫外光雷射照射時仍可保有高光電增益特性。最後，論文中提出一個簡單的方法來製作氧化鋅奈米帶網絡的紫外光偵測器，且證明該偵測器無論在光電流表現以及動態反應上都表現良好。這是由於奈米帶間的接觸產生了能量障壁並阻礙了電子的傳輸，而在照光時由於能量障壁的減弱，使得元件表現出對光的高敏感性。結果顯示，氧化鋅奈米帶網絡的光偵測器具有製程便宜且高效能表現的優點，並對於以奈米結構為基礎的大面積化光電元件提供了另一種觀點。

關鍵字

氧化鋅；奈米線；光偵測器；光電流；奈米金粒子

並列摘要

In this thesis, the mechanisms of photoconductivity in ZnO nanowires (NWs) are discussed in detail, and the improvement methods for nanowire photodetectors (PDs) are proposed and discussed. First of all, since surface effects are widely recognized to greatly influence the properties of nanostructures, we report the evaluation of the surface effect on the photocarrier relaxation behavior by using a single ZnO NW ultraviolet (UV) photodetector. The pronounced surface effect leads to the enhanced-mode device behavior and the space-charge-limited transport of a single ZnO NW PD in dark. In the recovery phase, the decay of photocurrent is found to be strongly related to the power of UV light and the diameter of NWs, indicating that the photocarrier relaxation behavior is dominated by the surface band bending. A model for the relaxation behavior based on the surface band bending of NWs is proposed to interpret the experimental results. Second, we demonstrate the Au nanoparticle (NP) decoration as an effective way to enhance both photocurrent and photoconductive gain of single ZnO NW PDs through localized Schottky effects. The enhancement is caused by the enhanced space charge effect due to the existence of the localized Schottky junctions under open-circuit conditions at the NW surfaces, leading to a more pronounced electron-hole separation effect. Since the band-bending under illumination varies relatively small for an Au NP-decorated ZnO NW, the decay of gain is less prominent with increased excitation power, demonstrating the feasibility for a PD to maintain a high gain under high-power illumination. Finally, an efficient way to fabricate ZnO nanobelt (NB) networks as UV PDs is proposed. The network PDs are demonstrated to show high sensitivity to UV light and exhibit fast photoresponse and recovery behaviors. The high performance is resulted from an additional conduction mechanism that is not available for single nanowire devices. The NB-NB junctions in a network device act as energy barriers to hinder the carrier transportation, and the reduction of energy barriers under illumination accounts for the high photosensitivity of NB network PDs. These results suggest that ZnO NB networks could be promising for inexpensive PDs and applicable on other large area nanostructure-based optoelectronics devices.

並列關鍵字

ZnO ； nanowire ； photodetecto ； photocurrent ； Au nanoparticle

參考文獻

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氧化鋅奈米線光電流特性之研究

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