奈米尺度下的光處理

Nanoscale Design to Enable the Photon Management

徐嘉陽(Chia-Yang Hsu)

指導教授 ： 何志浩

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.01625

摘要

近來奈米結構相對於大尺寸結構有較好的效能表現，然而，每個奈米材料都有自己的限制導致未來發展的應用，為了去突破這個限制，在我們的研究當中嘗試結合兩種奈米材料，藉由原子層沈積技術，做成了氧化鋅、二氧化鈦包覆多層奈米碳管的核殼奈米結構，且氧化鋅、二氧化鈦的厚度可以被精確控制。由於資安通訊在未來的應用，一個靈敏且偵測快速的偵測器是相當地被需要，在我們的實驗中發現這樣的一個核殼奈米線不只保有金氧半導體的高增益特性同時也大大地改善它的反應速度，這樣的一個材料提供了多功能的發展可看性，此外，我們提出一個模型去解釋高增益與快速反應。
首先，在多層奈米碳管-二氧化鈦的核殼奈米結構下，製作出寬能帶、快速且高靈敏的光偵測器，高增益可以達到104、反應時間4.4毫秒、回復時間10.2毫秒，由於核殼結構在徑向方向能夠分離載子，它能夠去幫助載子收集的效率，我們藉由光電流、反應時間的量測去探討多層奈米碳管與二氧化鈦之間的反應。高增益、快速反應、快速回復都來自於氧相關的電洞侷限以及在多層奈米碳管與二氧化鈦之間徑向蕭基電場，除此之外，這樣的一個核殼結構奈米線也具有發展光伏電池的潛能。
最後，由於外太空探索與光通訊的發展，吸收紫外光的自行供能元件是被大量地需要，我們利用了核殼結構奈米線的優點，製作出極快速也自行供能的紫外光波段的光偵測器，近來用奈米線排列的基底陣列廣泛地研究於自行供能元件，但是卻少有用單根奈米線去驅動實際的元件，多層奈米碳管-氧化鋅的核殼奈米線在波段325奈米下的雷射光具有200 A/W響應、高增益可達800，同時在無外界偏壓提供下能夠持續地驅動液晶顯示器，除此之外，多層奈米碳管-氧化鋅的核殼奈米線在真空下依然有高反應速度的表現，反應時間29毫秒、回復時間30毫秒，這都來自於徑向蕭基介面與薄膜氧化鋅的優點，我們以核殼奈米結構提供了多功能的可看性應用。

關鍵字

核殼 ； 奈米碳管 ； 光偵測器 ； 奈米線 ； 蕭基 ； 二氧化鈦 ； 氧化鋅 ； 自行供能

並列摘要

Nanostructures have shown great potential toward better performance than their bulk counterparts. However, every nanomaterials have their own limits, and thus future applications are being hindered. For making a breakthrough, in this study, we show a possible solution by combining two different nanomaterials together. By means of atomic layer deposition, the core-shell multiwalled carbon nanotubes (MCNTs)-TiO2/ZnO nanostructures could make the thickness control accurate. Duo to the potential applications of secure communication, a sensitive and fast photodetector (PD) is strongly desirable. However, the core-shell nanowires (NWs) not only converse the high photoconductive gain of the metal oxide semiconductor but also further promote the response speed. This material may pave a promising way for multifunctional NW-based optoelectronics in the future. In addition, a model concerning the connections between two materials is proposed to explain the high photoconductive gain and the fast response speed.
First of all, a broadband, fast, and sensitive PD is realized on the basis of MCNT-TiO2 core-shell NW geometry. The devices exhibit high photoconductive gain up to 104 and fast response/recovery times of 4.4/10.2 ms. Advances in the carrier separation occurred in the radial junction in core-shell architecture, the collection of charge could be enhanced. Herein, the interaction between MCNT and TiO2 is demonstrated by photocurrent generation and temporal behavior under varying wavelength illumination. The high photoconductive gain and fast response/recovery times are attributed to the presence of oxygen-related hole-trap states at the NW surface and the radial local electric field between MCNT cores and TiO2 shells duo to Schottky junctions. Furthermore, duo to the optoelectronic properties of core-shell NW, the material has great potential in photovoltaic cells applications.
Finally, for astronomical studies and optical communication, self-powered UV devices are much more desired. Herein, we employ the advantages of core-shell nanostructures to fabricate ultrafast, and self-powered ultraviolet (UV) PDs. Although the self-powered devices have been studied recently on the basis of NW-aligned arrays, little attention has paid on driving practical device by a single NW. We not only demonstrate sensitive MCNT-ZnO core-shell NW device with responsivity of 200 A/W and photoconductive gain of 800 under UV laser (325 nm, 100 mW/cm2) but also operate without an external power supply to continuously drive a commercial liquid crystal display. Furthermore, we show the first fast-speed demonstration of MCNT-ZnO-based PDs in vacuum condition with response/recovery times of 29/30 ms duo to the advantages of radial Schottky junctions and thin ZnO shells. We provide multifunctional coaxial nanostructures for the promising application in the future.

並列關鍵字

Core-shell ； Carbon nanotubes ； Photodetector ； Nanowire ； Schottky ； TiO2 ； ZnO ； Self-powered

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