二維過渡金屬硫化物擁有多元且適合發展高效能奈米電子元件以及奈米光電元件的物理特性。舉例來說，二硫化鎢擁有高螢光量子轉換效率，二硒化鉬的激子與帶電激子展現出賽曼效應，二硒化鈮在低溫下會展現超導現象等等。傳統半導體材料在進行異質介面設計時必須考量到不同材料之間的晶格結構與鍵結，然而二維過渡金屬硫化物層與層之間是由微弱的凡德瓦力所維繫，再者，每層二維過渡金屬硫化物都滿足八隅體原則，因此，二維過渡金屬硫化物在進行異質結構設計及材料堆疊都十分容易。此外，二維過渡金屬硫化物與現存半導體技術的高匹配性更加速了二維過渡金屬硫化物在近幾年的發展。在眾多的二維過渡金屬硫化物中，二硫化鉬的穩定化性、電子特性以及可見光的光學特性使得它被廣泛的研究。二硫化鉬的物理特性也使得它成為二維過渡金屬硫化物中最適合運用在可見光探測的材料。然而二維二硫化鉬的原子尺度厚度限制了材料的光質交互作用。本論文旨在藉由結合二維二硫化鉬與不同種的電漿子超材料來大幅度增強二硫化鉬在可見光範圍內的光電轉換效率。
貴金屬奈米結構可以在奈米結構周圍藉由局域表面電漿子共振以及表面電漿子震盪來增益以及侷限入射電磁波。因此，結合二維二硫化鉬與貴金屬奈米結構可以增加散射截面與增益局部光質交互作用。除了電漿子增益以外，基板的不同也會造成二維二硫化鉬的光學與電學特性的不同。懸空的二維二硫化鉬有更強的螢光效應和光柵效應，這些特性有利於增強二維二硫化鉬的光電轉換效率。在本論文的第一個研究中，我們同時利用電漿子增益以及薄膜懸浮的特性來增益二維二硫化鉬光感測器的元件表現。我們複合二維的二硫化鉬、一維的矽奈米線陣列以及零維的奈米銀顆粒來達成高效能光感測複合材料。二維二硫化鉬作為光電轉換材料以及載子通道。一維矽奈米線陣列作為基板支撐二硫化鉬懸浮、提供抗反射功能以及作為增加奈米銀顆粒密度的支架。銀奈米顆粒藉由局域表面電漿子共振來增益入射光的電場強度以及二硫化鉬的光質交互作用。我們的三元複合結構在無背閘極電壓的情況底下可以在532奈米波長雷射入射下響應度達到402.4 安/瓦。由於元件的高響應度以及大元件面積，元件的靈敏度也達到了2.34×1012 瓊斯。
在我們的第二個研究中，我們設計了一個全由半金屬-二硫化鉬介面所組成的電漿子增益光電感測元件。我們整合了二維二硫化鉬、鉍金屬電極以及鉍金屬電漿子奈米圓盤來增強二硫化鉬光感測器的元件表現。二維過渡金屬硫化物的電極電阻主要源自於與金屬接觸時所產生的費米能階釘扎效應，這會使光電流在流經電極時造成額外耗損並提高元件的耗能。利用鉍金屬的半金屬能帶可以壓抑二維過渡金屬硫化物的費米能階釘扎效應並形成歐姆接觸，因此可以減少光電流耗損。除了貴金屬可以形成表面電漿子外，鉍金屬的介電常數在可見光範圍內也可以形成局域表面電漿子共振。我們設計了一個在二硫化鉬吸收峰共振的鉍金屬奈米圓盤並與二硫化鉬複合，我們的結果顯示二硫化鉬在與奈米圓盤複合後於600 奈米波長的光電轉換效率增強了超過四倍。我們的全半金屬電漿子光感測元件的光響應表現相較二硫化鉬光感測元件增益了690％。元件的靈敏度達到了6.40×1012 瓊斯。本論文展示了利用多功能奈米結構與多功能半金屬可以設計出高效能、低耗能的二維過渡金屬硫化物光電元件，為未來的奈米元件設計提供了一個新的方向。

Atomically thin transition metal dichalcogenides (TMDCs) have great potential for realizing high-performance nanoelectronic and optoelectronic devices due to their various and intriguing physical properties. For example, WS2 possesses a high photoluminescence quantum efficiency, MoSe2 exhibits Zeeman splitting for the neutral exciton and the trion, and NbSe2 exhibits a superconducting property at low temperatures, etc. Unlike conventional semiconductor materials, which rely on lattice matching and covalent bond formation to generate heterostructure interfaces, the weak Van der Waals force between each TMDC crystal layer allows easy material stacking among different TMDCs. Moreover, the high compatibility of TMDCs with existing semiconductor technologies accelerates the development of the material. Among various TMDC materials, molybdenum disulfide (MoS2) has been intensely studied owing to its chemical stability, electrical properties and optical properties in the visible spectrum. The physical properties of MoS2 make it the most suitable TMDC for visible photodetection. However, there is a detrimental property that hinder the optoelectronic performance of MoS2 photodetectors. The atomically thin nature of monolayer and few-layer MoS2 limits their absorption and light-matter interaction. Therefore, in this dissertation, we investigated two approaches to drastically enhance the optoelectronic performance of MoS2 in the visible spectrum via integrating MoS2 with plasmonic nanostructures.
Noble metal nanostructures are able to substantially intensify and localize incident electromagnetic field by means of localized surface plasmon resonance (LSPR) or surface plasmon resonance (SPR). Combining MoS2 with plasmonic nanostructures can drastically increase scattering cross section and enhance local light-matter interaction. In addition to plasmonic enhancement, the substrate effect strongly influences the optical and electrical properties of 2D MoS2 as well. Suspended MoS2 has been shown to exhibit higher photoluminescence intensity and strong photogating effect, which can be employed in photodetectors. In our first study, we propose an approach to utilize plasmonic nanostructures and physical suspension for MoS2 photosensing enhancement by hybridizing 2D bilayer MoS2, 1D silicon nanowires (SiNWs) and 0D silver nanoparticles (AgNPs). MoS2 acts as the optoelectronic material and the carrier channel. The SiNW structure acts as a multifunctional substrate which suspends the MoS2 film, provides an anti-reflection property and accommodates more AgNPs. The AgNPs resonate with the incident electromagnetic wave and enhances the light-matter interaction of the surrounding MoS2. The hybrid structure shows a gateless responsivity of 402.4 A/W at a wavelength of 532 nm, which represents the highest value among the ever-reported gateless plasmonic MoS2 photodetector. The great responsivity and large active area results in an exceptional detectivity of 2.34×1012 Jones.
In our second study, we designed an all-semimetal plasmonic photodetector that consist of monolayer MoS2 integrated with Bi contact electrodes and Bi plasmonic nanodisks. The contact resistance originated from the Fermi-level pinning effect leads to high power consumption and poor photocurrent transport capability in MoS2 photodetectors. By utilizing Bi as the contact metal, the Fermi-level pinning effect at the metal-semiconductor interface is suppressed, which increases response speed and reduces photocurrent loss to contact resistance. Bi can not only suppress the Fermi-level pinning but also excite LSPR in the visible spectrum. The strongly localized electromagnetic field across the interface between Bi plasmonic structures and MoS2 is able to enhance the photon to exciton conversion efficiency over 4 times at 600 nm. Photoresponsivity of this all-semimetal MoS2 photodetector shows a 690% enhancement compared to the pristine device with conventional electrodes. In addition, detectivity of our device reaches 6.40×1012 Jones, which is the highest value reported for plasmonic MoS2 photodetectors. This dissertation demonstrates that integrating TMDCs with multicomponent nanostructures and multifunctional semimetal offers a new approach for realizing high-performance and energy-efficient TMDC optoelectronic devices.

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