奈米金屬光柵與共振腔應用於增強矽量子點的量子侷限放光效應

Abstract

以矽材料為基礎的光電子元件 (Silicon-based Optoelectronic devices)，是未來整合光互聯 (Optical Interconnects) 和互補式金屬氧化物半導體 (CMOS) 系統，很重要的研究方向。特別是以矽量子點 (Silicon Quantum Dots) 為發光源的發光元件，被認為是高速傳遞訊號的光互聯系統中最重要的元件。因此，如何去提升矽量子點元件的發光特性並研究其物理機制，是很重要的研究方向。 本論文成功研製世界上第一個具金屬-介電質-金屬奈米共振腔結構(Metal-Insulator-Metal Nano-cavity) 的非晶矽量子點發光源 (Amorphous Silicon Quantum Dots Light Emitter)，並深入分析與驗證其新穎的放光增強物理機制。此研究利用光場模擬去設計最佳化與對照組奈米結構，並實驗性的去驗證利用表面電漿子 (Surface Plasmons) 提升非晶矽量子點放光特性的各種新穎的物理機制。 本論文提出一個新穎的物理機制，是世界上第一個利用奈米金屬光柵 (Metal Nano-gratings) 的侷域性表面電漿共振效應 (Localized Surface Plasmons Resonances, LSPRs)，與奈米共振腔 (Nano-cavity) 中的共振腔模態耦合效應 (Modes Coupling)，成功有效提升奈米共振腔中的非晶矽量子點的輻射性複合量子侷限放光特性 (Quantum-Confinement-Induced Radiative Emission) 的研究。此新穎的物理機制有效提升非晶矽量子點發光元件的發光強度 (Emission Intensity)，以及大幅度改善全世界應用表面電漿子窄化矽量子點放光頻譜的程度(Bandwidth narrowing)，窄化其半高寬值 (Emission Bandwidth) 至只有15 nm，有效增加矽量子點發光源應用在光互聯系統中的實用性。此外，我們成功的在低溫環境之下成長出矽量子點 (below 450℃)，使得矽量子點在互補式金屬氧化物半導體系統整合中，更具有實用性的應用。 本論文主要的研究可以分成三個部分: 第一部份 (第四章)，此研究是世界上第一個利用Fabry–Pérot type LSPRs效應，有效提升非晶矽量子點發光強度的研究。我們利用電子束微影技術 (E-beam Lithography) 製作奈米金屬光柵，研究奈米共振腔中的表面電漿子彼此之間的共振耦合效應，成功的使奈米共振腔中的表面電漿共振，呈現侷域性的表面電漿共振子 (Localized Surface Plasmon, LSPs)，並在奈米金屬線的側壁 (sidewall) 呈現Fabry–Pérot resonance型態，並在量子力學的物理基礎下，耦合非晶矽量子點和表面電漿子的近場強電場 (strong near-field)，有效提升非晶矽量子點發光元件的發光強度。 第二部份 (第五章)，此研究是世界上第一個利用具結構對稱性的次波長奈米金屬交叉光柵 (Subwavelength Crossed Metallic Gratings)，有效提升非晶矽量子點發光強度的研究。我們設計具有結構對稱性的次波長奈米金屬交叉光柵以及次波長奈米共振腔結構，成功的利用其較強的表面電漿共振耦合輻射效應 (Out-coupling)，以及較高的光萃取效率 (Light-Extraction Efficiency)，並在量子力學的物理基礎下，耦合非晶矽量子點和表面電漿子的近場強電場，大幅度有效的提升非晶矽量子點發光元件的發光強度。 第三部份 (第六章)，此研究是世界上第一個成功利用次波長奈米共振腔中的侷域表面電漿模態 (Localized Surface Plasmon mode, LSPs mode) 與光學上的共振腔模態 (Optical Fabry–Pérot cavity mode) 互相耦合的效應，有效提升非晶矽量子點發光強度的研究。此研究成功改善非晶矽量子點發光元件的發光特性，和沒有奈米金屬陣列結構的元件互相比較，優化的奈米金屬光柵發光元件，其發光峰值可大幅提升2.77倍，並且，其發光頻譜半高寬縮小至只有15 nm，有效增加矽量子點發光源應用在光互聯系統中的實用性。 本論文提出一個具有實用性的次波長奈米共振腔搭配奈米金屬光柵結構，在量子力學、表面電漿共振，以及奈米共振腔的物理基礎下，成功耦合非晶矽量子點、表面電漿模態，以及共振腔模態，有效提升非晶矽量子點發光元件的發光特性，有效增強矽量子點發光源應用在光互聯系統中的實用性。

The development of Si-based optoelectronics integrated circuit (OEICs) devices is the key issue for the integrations of optical interconnects (OIs) and complementary metal oxide semiconductor (CMOS) technologies in the future. For the practical applications of Si-based OEICs in future Central Processing Unit (CPU) with high-speed data rates, the key component is the light source – Si quantum dots (Si QDs) light emitter. Hence, how to improve the light emission properties of the Si QDs light emitter and figure out its fundamental physical mechanisms, those are very important issues and research directions in the future. This thesis successfully developed the world's first amorphous silicon quantum dots (a-Si QDs) light emitter with metal-insulator-metal (MIM) sandwiched nanostructures, and we deeply analyzed and verified its new physical mechanism for light emission. We designed the nanostructures of optimized and reference sample by advanced optical simulation, and we experimentally verified the correctness of the new physical mechanism for surface plasmons-enhanced light emission from a-Si QDs light emitter. We do the world's first research of new physical mechanism of the mode coupling between the localized surface plasmons resonances (LSPRs) mode and the optical cavity mode in the MIM nanocavity. This new physical mechanism successfully enhanced the quantum-confinement-induced emission output of a-Si QDs, and greatly narrowed the emission bandwidth to only 15 nm, compared to the related study of spectral narrowing by surface plasmons resonance in the world. The thesis focuses in depth on the experimental researches and analysis for the enhancements of light emissions of the a-Si QDs light emitter with the MIM sandwiched nanostructures, and its basic physical mechanisms. We have successfully shown that the multifold intensity enhancements and spectral narrowing of photoluminescence of the a-Si QDs light emitter, through the coupling of the a-Si QDs and the near-field (evanescent electric field) of the localized surface plasmons (LSPs), the out-coupling effect of LSPs, and the strong coupling effect between the LSPs and optical Fabry–Pérot (FP) resonance modes in the coupled QDs–plasmonic system, based on the theories in quantum mechanics (QMs), surface plasmon (SPs), and nanocavity, by tuning the plasmonic subwavelength metallic nano-gating on the top. Besides, the Si QDs have been successfully grown by the low-temperature annealing (below 450 ℃), providing more practical applications of the Si QDs integrated into the CMOS system. The thesis has three main parts: The first part (Chapter 4), we investigated experimentally the world's first research of plasmon-enhanced light-emission of the a-Si QDs light emitter with the Ag/SiOx:a-Si QDs/Ag nanostructures, through the resonant coupling between the a-Si QDs and the near-field of FP-type LSPs resonance mode, by tuning a one-dimensional (1D) Ag gratings on the top. According to our experimental results, it is worthwhile noticing the improved design of Ag grating structure by tuning the pitch and Ag line width for the largest PL integrated emission through the strong a-Si QDs–LSPs coupling, based on the theories of QMs and SPs. The second part (Chapter 5), we have experimentally investigated the world's first research of LSPs-enhanced PL intensity and spectral narrowing of the a-Si QDs, using plasmonic subwavelength crossed Ag gratings as the top layer in the Ag/SiOx:a-Si QDs/Ag sandwich nanostructures. A 2-fold enhancement in the PL peak intensity and a 1.34-fold enhancement in the integrated PL intensity have been observed by switching the 1D Ag grating to the crossed Ag grating, through the higher light-extraction efficiency of the polarization-independent symmetric structure, the stronger a-Si QDs–LSPs coupling, and the increased out-coupling efficiency of the LSPs mode to the radiated photons. The third part (Chapter 6), we have experimentally demonstrated the world's first research of the amplified PL emission with narrowed linewidth of the a-Si QDs, through the strong coupling of the LSP and optical FP cavity modes within the MIM plasmonic nanocavity, at the emission peak wavelength of free a-Si QDs. As compared with the results of our previous report (Chapter 4), the significant spectral narrowing is achieved by further applying the resonance coupling between the LSP and optical FP cavity modes by the whole new configuration designs of the MIM plasmonic nanocavity. A maximum of 2.77-fold PL enhancement and the narrowest emission linewidth of 15 nm have been observed by using an optimized 1D Ag grating structure as the top layer in the nanocavity. A novel MIM sandwich nanocavity combined with the plasmonic subwavelength metallic gratings was proposed for efficiently enhancing the light-emission properties of a-Si QDs, through the exctions-plasmons coupling in QD–plasmonic material system, the strong out-coupling of LSPs, and the strong coupling between the LSPs and optical FP cavity modes, for the practical applications of a-Si QDs as a promising light source in future OEICs integrated with CMOS systems.