具金屬結構的氮化銦鎵/氮化鎵量子井發光元件及雷射成形金屬奈米顆粒之表面電漿子特性分析

在本論文中，我們首先研究與金屬結構有關的表面電漿子和藍光氮化銦鎵量子井之間的耦合作用；實驗使用的樣品中，金屬結構距離量子井10奈米。我們比較在半導體表面蒸鍍銀薄膜和銀奈米顆粒時，表面電漿子和量子井耦合作用的差異。實驗發現，光激螢光強度的減弱程度和時域解析螢光頻譜的衰變速率皆與金屬的表面型態有關。我們也建立了一個表面電漿子和量子井耦合過程中載子釋放現象的速率方程式模型，用以進一步擬合分析時域解析螢光頻譜並獲取載子與表面電漿子的衰變期時間常數。再者，我們分析在表面電漿子和量子井耦合過程中，量子史塔克效應的載子屏蔽效應對增強量子井放光的影響。我們先進行變激發功率光激螢光和時域解析螢光頻譜實驗，再利用衰變速率方程式模型擬合時域解析螢光頻譜的數據。分析發現當激發變強，量子史塔克效應的載子屏蔽效應不僅增強發光，同時也因為放光頻譜的藍移而增強表面電漿子的耦合效率。因為如此，相較於純粹量子井放光，來自表面電漿子放光的比例會隨著激發強度而增強。此外在擬合分析中也發現表面電漿子和量子井的耦合強度會隨著激發強度增強而有飽和現象。此外，我們也利用一個與鄰近銀金屬光柵具有表面電漿子耦合作用的氮化銦鎵雙層量子井結構，分析單一維度銀金屬光柵結構中表面電漿子的特性。我們建構了一套角度解析光激螢光光譜自動量測系統，以記錄量測表面電漿子的特徵。我們觀察到具有特定偏光特性的螢光，其來源是經由光柵繞射提供動量匹配的表面電漿子。此外我們也利用了觀測到的電漿子色散曲線，測定出表面電漿子的群速度。我們也驗證了在實驗中使用的金屬光柵，可以經由改變其周圍環境介質而改變其表面電漿子的色散特性。最後，我們展示一種利用波長266奈米的脈衝雷射照射，在不同基板(包含藍寶石，氮化鎵，二氧化矽)上製作近似球型的金奈米顆粒的方法。金奈米顆粒的粒徑、與基板的接觸角、顆粒密度和表面覆蓋百分比可利用以下參數控制：雷射能量密度、基板種類、雷射照射時覆蓋金薄膜氣體或液體。因為奈米顆粒排列具有固定的方向性，光學穿透量測顯示此種奈米顆粒具有明顯的平面和非平面的表面電漿子共振特徵。這些特徵中，似空氣共振態主要受奈米顆粒所處介質影響；平面基板共振態受基板材料和接觸角影響；非平面共振特徵則明顯地受基板材料和接觸角影響。利用有限元素法得到的數值模擬結果顯示出與實驗一致的侷域性表面電漿子共振頻譜變化特徵。模擬結果也顯示出奈米顆粒的吸收與散射效率對其光滅減率的影響。這種以簡單的雷射照射製作而成的金奈米顆粒具備固定方向性、奈米顆粒間不易聚集與牢固的基板附著等特點，可應用於具偏振靈敏度的侷域性表面電漿子共振生化檢測技術上。

關鍵字

surface plasmon；InGaN；nanoparticle；laser irradiation；gratings；dispersion

並列摘要

In this dissertation, we first study the metallic-structure dependent surface plasmon (SP) coupling behaviors with a blue-emitting InGaN/GaN quantum well (QW), which is 10 nm away from the metallic structures. The SP-QW coupling behaviors in the areas of semiconductor surface coated with Ag thin film and Ag nanoparticles are compared. It is found that both the suppression of photoluminescence (PL) intensity and the reduction of time-resolved PL (TRPL) decay time strongly depend on the metallic morphology. A phenomenological rate-equation model of carrier relaxation in the SP-QW coupling process is built to fit the TRPL decay profiles for calibrating the reasonable decay time constants of carrier and SP. Next, we analyze the contribution of the screening of the quantum-confined Stark effect (QCSE) to the emission enhancement behavior in the process of SP coupling with an InGaN/GaN QW, which is 20 nm away from an Ag thin film that supports the SP. From the measurements of excitation power-dependent PL and TRPL spectroscopy, and the fitting to the TRPL data based on the modified rate-equation model, it is found that when the excitation level is high, the QCSE screening effect not only contributes significantly to the emission enhancement, but also increases the SP coupling rate because of the blue shift of emission spectrum caused by the screening effect. Therefore, the emission strength from SP radiation, relative to that from QW radiative recombination, increases with the excited carrier density. Also, a saturation behavior of SP-QW coupling is observed from the fitting procedure. Besides, we report the characterizations of the SP features on a 1-D Ag-grating structure through the SP coupling with an InGaN/GaN dual-QW structure closely below the metal grating. We build an angle-resolved PL measurement system to observe the SP features. Polarized photon output is observed because only the momentum matching condition of the SP mode propagating in the direction perpendicular to the grating grooves can be reached through the diffraction of the fabricated grating. Hence, the SP radiation efficiency is significantly enhanced only in this polarization. We also calibrate the group velocity of the observed SP mode from the measured dispersion curves. With the Ag-grating structure used in the experiment, the SP dispersion properties can be manipulated by changing the dielectric material surrounding the grating structure. Finally, we demonstrate the fabrications of sphere-like Au nanoparticles (NPs) of similar shapes and alignments on sapphire, GaN, and SiO2 substrates through the irradiation of a few pulses of 266-nm laser onto Au thin films deposited on the substrates. The top-view diameter, contact angle on substrate, surface population density, and surface coverage percentage of the NPs can be controlled by the Au thin film thickness, laser energy density, substrate choice, and the gas or liquid, in which the Au thin film is immersed during laser irradiation. Due to the fixed orientation of NPs, optical transmission measurements show clear in-plane and out-of-plane localized surface plasmon resonance (LSPR) features, including the air resonance feature dictated by the gas or liquid immersing the NPs during transmission measurement, the in-plane substrate resonance feature controlled by the substrate material and the contact angle, and the out-of-plane resonance feature, which is strongly influenced also by the substrate material and the contact angle. Numerical simulations based on the finite-element method using the experimental parameters show highly consistent LSPR spectral positions and their variation trends. From the simulation results, one can also observe the relative importance between NP absorption and scattering in contributing to the extinction. This simple laser-irradiation method for fabricating fixed-orientation sphere-like Au NPs of no aggregation and of strong adhesion to the substrate is useful for developing polarization-sensitive LSPR bio-sensing.

並列關鍵字

表面電漿；氮化銦鎵；奈米顆粒；雷射照射；光柵；色散

參考文獻

1. W. P. Halperin, “Quantum size effects in metal particles,” Rev. Mod. Phys. 58, 533 (1986).

2. P. Drude, “Zur Elektronentheorie der Metalle,” Ann. Phys. 1, 566–613 (1900).

3. P. Johnson and R. Christy, “Optical Constants of the Noble Metals,” Phys. Rev. B. 6, 4370(1972).

5. H. Ditlbacher, A. Hohenau, D. Wagner, U. Kreibig, M. Rogers, F. Hofer, F. R. Aussenegg, and J. R. Krenn, “Silver Nanowires as Surface Plasmon Resonators,” Phys. Rev. Lett. 95, 257403 (2005).

6. C. Sönnichsen, T. Franzl, T. Wilk, G. von Plessen, and J. Feldmann, “Drastic Reduction of Plasmon Damping in Gold Nanorods,” Phys. Rev. Lett. 88, 077402 (2002).

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具金屬結構的氮化銦鎵/氮化鎵量子井發光元件及雷射成形金屬奈米顆粒之表面電漿子特性分析

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