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標題: | 發光二極體內表面電漿子耦合行為之理論與數值研究 Theoretical and Numerical Studies of Surface Plasmon Coupling Behaviors in a Light-Emitting Diode |
作者: | Yang Kuo 郭仰 |
指導教授: | 江衍偉 |
關鍵字: | 侷域表面電漿子,輻射偶極,金屬奈米粒子,反饋效應,發光二極體, localized surface plasmon,radiating dipole,metal nanoparticle,feedback effect,Light-Emitting Diode, |
出版年 : | 2013 |
學位: | 博士 |
摘要: | 本論文中,我們根據半古典模型提出一套處理侷域表面電漿子(LSP)與輻射偶極間耦合的理論公式。此套公式考慮了LSP對偶極行為的反饋效應。藉此理論,我們發表了一些數值結果,包括偶極強度變化與系統總輻射功率增強之頻譜及其與偶極-奈米粒子間距的關係等,並作了說明與解釋。結果顯示,偶極與LSP耦合可以增強總輻射功率。由於反饋效應的引入,使得偶極強度增強,總輻射功率的增強效果更為明顯。我們發現徑向偶極輻射功率的增強主要來自LSP偶極共振模態的耦合,而切向偶極之增強則主要來自高階LSP共振模態的耦合。這些結果可以用偶極的輻射與LSP模態的輻射間的干涉效應以及銀奈米球的波長相依性吸收行為來解釋。我們亦論及在InGaN/GaN 量子井中偶極實際的指向對LSP耦合的影響。LSP耦合強度或輻射功率增強不受限於金屬結構近場分布的穿透深度。論文中亦討論兩個偶極與一個金屬奈米粒子上LSP的耦合行為。在此耦合過程中有三個機制造成輻射功率增強:兩個偶極相位延遲造成的干涉現象、兩個偶極間的交互作用,以及LSP共振耦合。結果顯示總輻射功率的增強與起始相差以及兩個偶極的相對位置有關。最後,我們探討了在GaN材質中的輻射偶極與表面銀奈米粒子感應的LSP共振模態耦合所造成的輻射功率增強。從輻射功率增強之頻譜圖可以看出對應於LSP偶極模態與高階模態的頻譜峰值。模態場主要分布在銀奈米粒子的底面,使得增強的輻射功率大部分向下輻射。頻譜峰值一般隨偶極與銀奈米粒子間的距離增加而紅移。對特定波長而言,輻射功率增強未必然隨距離增加而遞增。藉由輻射極子的橫向移動,輻射功率增強的頻譜峰值會紅移,且峰值大小隨著橫移距離增加而減小。 In this dissertation, we propose theoretical formulations of the localized surface plasmon (LSP) coupling with a radiating dipole based on a semi-classical model, in which the feedback effect of LSP on the dipole behavior is included. We report the numerical results of LSP-dipole coupling based on the proposed model. The spectral and dipole-nanoparticle distance dependencies of dipole strength variation and total radiated power enhancement of the coupling system are demonstrated and interpreted. The results show that the dipole-LSP coupling can enhance the total radiated power. The enhancement is particularly effective when the feedback effect is included and hence the dipole strength is increased. We find that the enhancement of radiated power of a radial dipole is induced through the coupling with the LSP dipole resonance. On the other hand, that of an orbital dipole is mainly induced through the coupling with the higher-order LSP resonance. These results are interpreted with the interference behaviors between the radiations of the source dipole and the LSP mode and with the wavelength-dependent absorption behaviors of the Ag nanosphere. The LSP coupling behaviors in considering the practical situation of dipole orientation in an InGaN/GaN quantum well are also discussed. It is learned that the LSP coupling strength or radiated power enhancement is not limited by the penetration depth of the near field distribution induced around the metal structure. We also discuss the coupling behaviors between two radiating dipoles and LSP induced on a nearby Ag nanoparticle (NP). Three mechanisms are involved in the coupling process for radiated power enhancement, including the interference of the two phase-retarded dipole contributions, the interaction between the two dipoles, and the LSP resonant coupling. The results show that the total radiated power can be enhanced significantly, depending on the un-coupled relative phase and the relative position of the two dipoles. Finally, the radiated power enhancement of a radiating dipole within a GaN material coupling with LSP resonance modes induced on a surface Ag NP is demonstrated. It is found that the radiated power enhancement shows the spectral peaks corresponding to the dipole and higher-order LSP resonance modes with mode fields mainly distributed around the bottom of the Ag NP such that the enhanced radiated power is mainly in the downward direction. The spectral peaks generally red shift with increasing distance between the radiating dipole and the Ag NP. At a given wavelength, the radiated power enhancement does not necessarily decay monotonically with increasing distance. By moving the radiating dipole laterally away from the bottom of the Ag NP, the spectral peaks of radiated power enhancement red shift and their levels diminish with increasing lateral distance. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/61470 |
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顯示於系所單位: | 光電工程學研究所 |
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