Metal Nano-grating and Nano-cavity for the Enhancement of Quantum-Confinement-Induced Photoluminescence of Silicon Quantum Dots
Date Issued
2016
Date
2016
Author(s)
Tsai, Tsung-Han
Abstract
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.
Subjects
Silicon Quantum Dots (Si QDs)
Quantum Confinement Effect (QCE)
Photoluminescence (PL)
Surface Plasmons (SPs)
Localized Surface Plasmons (LSPs) mode
Optical Fabry–P?rot (FP) resonance mode
Subwavelength Nano-cavity
Subwavelength metallic nano-grating
Crossed grating
Metal-insulator-Metal (MIM) sandwich nanostructures
Near-field
Evanescent electric field
Mode coupling
Out-coupling of LSPs
Optical Interconnects (OIs)
Si-based optoelectronics integrated circuit (OEICs).
Type
thesis
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