以表面電漿子耦合效應製作偏振化發光二極體

Fabrication of Polarized Light-emitting Diodes Based on Surface Plasmon Coupling Effects

沈坤慶(Kun-Ching Shen)

指導教授 ： 楊英杰

共同指導教授 ： 楊志忠

國立臺灣大學/電機資訊學院/電子工程學研究所/博士(2010年)

https://doi.org/10.6342/NTU.2010.10641

摘要

在本論文中，我們研究了與金屬結構有關的表面電漿子和藍綠光雙波長氮化銦鎵量子井之間的耦合作用，分析單一維度銀金屬光柵結構中表面電漿子的特性。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。
其次，將金屬光柵提供之表面電漿子與量子井所產生的耦合效果運用於綠光發光二極體上。在已知的發光二極體研究文獻上，這是第一個證實使用金屬光柵所提供之表面電漿子與量子井耦合所產生之偏振特性發光二極體。為了滿足金屬光柵所提供之表面電漿子與發光二極體中的量子井耦合之有效距離，發光二極體的p型結構設定為70奈米。藉由電流注入激發量測，在適當的金屬週期結構，其整體輸出功率可提昇至200%，且輸出光之偏振比可達1.51。
除外，如何在發光二極體上，進一步改善表面電漿子與量子井的耦合效應也是本論文中的一個重點。我們採用一些介電物質來改變表面電漿子的共振頻率，使其表面電漿子的消散場分布範圍可以更深入量子井區，同時也配合金屬光柵的週期變化，以產生更大的耦合效應。從我們的電流注入激發量測，輸出光之偏振比可達1.81。此元件在取代液晶顯示器後端之光源與偏振片上，反映出極大潛力。

關鍵字

表面電漿子 ； 發光二極體

並列摘要

In this dissertation, we report the observation of a polarization-dependent surface plasmon (SP) feature on a 1-D Ag-grating structure through the SP coupling with an InGaN/GaN quantum-well structure beneath the metal grating. Because only the momentum matching condition of the SP component (TM mode) propagating in the direction perpendicular to the grating grooves can be reached through the scattering of the fabricated grating, the SP radiation efficiency is significantly enhanced only in this polarization. Hence, polarized photon output is observed. The dispersion curve of the observed SP mode shifts along the wavenumber axis according to the change of the metal grating period.
Next, the enhanced and partially polarized output of a green light-emitting diode (LED), in which its InGaN/GaN quantum well (QW) couples with surface plasmons on a surface Ag grating structure is demonstrated. Compared with another LED sample of flat Ag coating, the output intensity of the grating LED is enhanced by ~200 % and its polarization ratio reaches 1.51 when the grating period and groove depth are 500 nm and 30 nm, respectively. Based on the comparison with a sample of larger spacing between the metal and QW and numerical simulation, it is concluded that the output enhancement and polarization behaviors are mainly attributed to the QW coupling with localized surface plasmons generated on the grating grooves.
Finally, the output polarization ratio enhancement of an InGaN/GaN quantum well (QW) light-emitting diode (LED) with surface plasmon (SP) coupling by the insertion of a SiO2 layer between the p-GaN layer and a surface Ag grating structure is demonstrated. The insertion of the SiO2 layer is expected to reduce the metal dissipation of SP energy and to further extend the near-field distribution range of induced SP for effectively increasing the SP-QW coupling effect. The Ag grating period for optimizing SP-QW coupling is increased when a SiO2 layer is added to the device that is consistent with the simulation results of the momentum matching of surface plasmon polariton and the resonance of localized surface plasmon. The almost un-polarized outputs from other LED samples fabricated with an epitaxial structure of thicker p-GaN layer, which leads to weak SP-QW coupling, indicate that the observed polarization ratios are due to near-field SP-QW coupling, instead of far-field diffraction

並列關鍵字

surface plasmon ； LED

參考文獻

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