近年來雙波段紅外光電偵測器漸漸受到矚目，受到矚目主要原因是我們能利用雙波段紅外光電偵測器選擇感測不同波段的光，這些不同波段範圍的光分別代表不同的資訊，像是利用近紅外光成像可以描述物體的外觀，利用中紅外光成像可以了解物體的溫度，透過改變雙波段光偵測器的正負電壓，能選擇偵測不同波段的光，在日常、軍事各方面有很大的應用。

到目前為止這種雙波段光電偵測器大多主要都是使用三五族半導體來製作，但晶片化過程中，傳統三五族半導體整合在矽基板上會面臨一些問題，像是三五族半導體與矽的晶格常數差距大，在長晶過程會有晶格不匹配問題，甚至會產生接面應力集中問題，雖然此問題可藉由生長緩衝層來解決，但這會使得元件結構繁冗複雜。此外，傳統三五族感測器常需背負額外冷卻器來維持低溫操作穩定，這使得於元件體積大、成本高、產量低，也因此目前大多應用在軍事或是科學研究方面。而除了使用傳統半導體之外，近年來有研究團隊利用量子點來製作雙波段光電偵測器。與傳統三五族的光電偵測器相比，其優勢在於製程上只需要簡單旋塗均勻，可以大面積製作、成本較低、高性能，但在摻雜方面較不易維持穩定，需要在低溫下才能穩定操作。

不管是三五族半導體或量子點的材料在製程上都會遇到問題，相對於此，二維材料擁有許多不同能隙等優勢，可以解決以往三五族半導體或量子點的一些問題，本論文是以二維材料堆疊出雙波段凡德瓦異質結構的光電偵測器，在製程方面，因為二維材料沒有懸空鍵，可透過的凡德瓦力來堆疊晶格匹配限制外的其他材料，因此沒有像雙波段三五族異質結構光電偵測器有晶格不匹配的問題；另外在環境溫度上，沒有像雙波段量子點光電偵測器有一定限制，在常溫下也可以維持雙波段光偵測，操作上較為穩定。我們使用凡德瓦異質結構製作一pnp異質結構的元件，並利用掃描式光電流顯微鏡去分別驗證pn和np的兩個異質結構是可以形成交錯型(Staggererd gap, Type-II)的結構，在利用光電流量測方法，分別在pnp元件重疊區域照射633nm、1064nm、3400nm不同波段的光，透過改變正負電壓，選擇偵測不同波段的光，當施加正電壓可以偵測可見光、近紅外光波段，當施加負電壓可以偵測中紅外光波段，在偵測可見光波段，其光響應可以達到~156 mA⁄W；在偵測近紅外波段，其光響應可達約~223 mA⁄W；在偵測中紅外波段，其光響應為約~56 mA⁄W，透過這些量測結果證明使用二維材料來堆疊一個雙波段pnp異質結構元件進行近紅外/中紅外光感測是可行的。此雙波段元件的電壓選擇機制在光子偵測器中受到極大關注，在未來可望發展不同種類的雙波段光電偵測器，並應用到各領域，例如：自駕車的駕駛輔助系統或長照方面等。

Bias-selectable dual-band infrared photodetectors have recently attracted great attentions, because they can find application in a wide variety of fields, such as night vision, security, medical imaging and environmental sensing. So far, most of dual-band photodetectors are mainly made of III-V group semiconductors. But fabricating these III-V devices is quite challenging, as it is necessary to grow multiple buffer layers to avoid the thermal stress formed at heterointerfaces. Furthermore, those devices generally require cryogenic cooling. This not only leads to the bulky system, but also increase the cost of optoelectronic components. An alternative approach is to utilize quantum dots to fabricate bias-selectable dual-band infrared photodetectors. Although quantum dots-based devices can be easily made due to their solution processibility, they still require low temperature operation.

In contrast, the recent discovered two-dimensional (2D) materials are considered as the promising candidates. This is because this 2D family has a wide range of optical band gaps, and different 2D materials can be stacked vertically to form van der Waals heterostructures without the lattice mismatching issue. In this thesis, we will report the first bias-selectable dual-band infrared photodetectors via utilizing van der Waals heterostructures. Specifically, the device is composed of vertically stacked pnp heterostructures. To characterize the heterostructures, we utilized the scanning photocurrent microscopy to resolve the position, where photocurrent can be generated, as well as to identify the band structures of heterojunctions. In addition, we observed our developed device can perform strong photoresponses in visible to near-infrared (mid-infrared) spectrums, as it is in positive (negative) biased region. The demonstrated photoresponsivity can be higher than tens mA/W, and our detector can be operated at room temperature condition. These features suggest its usefulness to practical applications.

致謝······················································I
摘要·····················································IV
Abstract·················································VI
目錄···················································VIII
圖目錄····················································X
Chapter 1 緒論············································1
Chapter 2 二維材料的簡介及其在光電元件上的應用···············7
2.1 二維材料的光電特性··································7
2.2 光電流機制介紹······································9
2.2.1 光伏效應(Photovoltaic effect, PVE)···············9
2.2.2 光電導效應(Photoconductive effects, PCE)·········12
2.2.3 光閘效應(Photogating effect, PGE)················15
2.3 雙波段異質結構光電偵測器····························17
Chapter 3 元件製作········································22
3.1 二維材料的製備·····································22
3.2 材料的轉移·········································23
3.3 二維材料異質結構···································25
3.4 雙波段二維材料異質結構光電偵測器·····················26
Chapter 4 量測結果········································29
4.1 由 MoTe2/MoS2組成的pn異質結構·······················32
4.2 由BP/MoS2組成的pn異質結構···························33
4.3 由BN/ Gr/MoTe2/MoS2/BP組成雙波段異質結構光電偵測器···36
Chapter 5 結論與未來展望··································46
參考文獻··················································49

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