具金屬奈米結構之表面電漿子耦合發光二極體

為使表面電漿子與量子井有效耦合以提升發光二極體效率,本研究中,我們於發光二極體上設計並製作三種不同之周期性金屬奈米結構，並利用此結構產生的表面電漿子和綠光發光二極體之量子井耦合，提升發光二極體之發光效率。第一個結構是在發光二極體上製作週期性的奈米銀突起陣列，藉由深入p型氮化鎵內的銀突起陣列結構，可以縮短銀金屬結構和量子井間的距離，誘發在銀尖端附近更強的近場和量子井產生耦合。結果顯示,當注入電流為100毫安培時，具有奈米銀突起陣列之發光二極體結構和發光二極體對照組相比，發光增強74.6%。此外，此結構之模擬吸收頻譜得到的共振波長和實驗之反射頻譜所得到之結果吻合。另外兩組表面電漿子耦合發光二極體結構是在不同厚度的p型氮化鎵之發光二極體上製作。第二組表面電漿子耦合發光二極體的結構是製作在厚的p型氮化鎵之發光二極體上。為了減少銀奈米顆粒和量子井間的距離以提升耦合強度，我們將銀的奈米顆粒放置在已蝕刻出週期性孔洞結構的p型氮化鎵內部，並將二氧化矽小球覆蓋孔洞的剩餘空間以降低漏電流。而第三組表面電漿子耦合發光二極體是將週期性排列的銀奈米顆粒放置在薄的p型氮化鎵之發光二極體上。為改善電流擴散我們於這兩組表面電漿子耦合之發光二極體、僅有孔洞結構之發光二極體，以及沒有任何結構之發光二極體表面利用分子束磊晶成長氧化鎵鋅作為透明導電層。儘管因為氧化鎵鋅的覆蓋導致表面電漿子共振波長紅移，使得量子井與表面電漿子的耦合變弱，但從內部量子效率及發光強度看，表面電漿子耦合發光二極體之效率都有明顯的提升。

關鍵字

發光二極體；表面電漿子；奈米壓印；三五族半導體；銀

並列摘要

For generating surface plasmon coupling (LSP) with the radiating dipoles in the InGaN/GaN quantum-wells (QWs) of green light emitting diodes (LEDs) and enhancing the LED emission, we fabricate three sets of SP-coupled LEDs. First, an Ag protrusion array is fabricated on the p-GaN layer of an InGaN/GaN QW LED for generating surface plasmon coupling with the radiating dipoles in the QWs and hence LED emission enhancement. The tips of the Ag protrusions penetrating into the p-GaN layer are close to the QWs such that the induced SP near field around the tips can strongly interact with the dipoles in the QWs. With the Ag protrusions, the fabricated flip-chip LED shows a 74.6 % enhancement compared with the control LED in output intensity at 100 mA in injection current. Besides, the simulation results of Ag protrusion absorption agree reasonably well with the experimental data of protrusion reflectance. Then the other two sets of SP-LEDs are based on two epitaxial structures of different p-GaN layer thickness. In the second set based on the epitaxial structure of thick p-GaN, to reduce the distance between the Ag nanoparticles (NPs) and the QWs for increasing the coupling strength, Ag NPs are filled into a hole array fabricated on the p-GaN layer. To minimize current leakage, SiO2 NPs are used to cover the Ag NPs in the holes. In the third set based on the epitaxial structure of thin p-GaN, Ag NPs are fabricated on the surface of p-GaN. The SP-LEDs and the control LEDs with flat surface or empty holes are covered with the transparent conductor GaZnO. The SP-LEDs show the significant enhancements of LED output intensity and internal quantum efficiency even though the coverage of GaZnO red-shifts the LSP resonance peak such that the QW emission can only couple with the short-wavelength shoulder feature of LSP resonance. With the Ag NP design in this work, the current leakage is significantly reduced.

並列關鍵字

light emitting diodes ； surface plasmons ； nano imprint lithography ； III-V semiconductors ； silver

參考文獻

1. R. H. Ritchie, “Plasma Losses by Fast Electrons in Thin Films,” Phys. Rev. 106, 874 (1957)

2. W. H. Chuang, J. Y. Wang, C. C. Yang, and Y. W. Kiang, "Differentiating the contributions between localized surface plasmon and surface plasmon polariton on a one-dimensional metal grating in coupling with a light emitter," Appl. Phys. Lett. 92, 133115, (2008).

3. W. L. Barnes, A. Dereux, and T. W. Ebbesen, "Surface plasmon subwavelength optics," Nature 424, 824 (2003).

4. J. R. Sambles, G. W. Bradbery, and F. Z. Yang, “Optical excitation of surface plasmons: an introduction,” Contemp. Phys. 32, 173 (1991).

5. E. Kretschmann, and H. Reather, “Radiative decay of non-radiative surface plasmons excited by light,” Z. Naturf. 23A, 2135, (1968).

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具金屬奈米結構之表面電漿子耦合發光二極體

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