Surface Plasmon Coupling with Radiating Dipole for Enhancing the Emission Efficiency and Light Extraction of a Deep Ultr
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Surface Plasmon Coupling with Radiating Dipole for Enhancing the Emission Efficiency and Light Extraction of a Deep Ultraviolet Light Emitting Diode Yafeng Yang 1 & Huiqing Sun 1,2
&
Yaohua Zhang 1 & Ha Su 1 & Xicheng Shi 1 & Zhiyou Guo 1,2
Received: 26 July 2019 / Accepted: 16 December 2019 # Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract In this paper, we numerically investigated the emission characteristics of surface plasmon (SP)-enhanced deep ultraviolet light emitting diode (DUV-LED) by employing Al/Al2O3 core-shell nanoparticle(NP) structure on the p-GaN contact layer by utilizing finite-difference time-domain (FDTD) method. The results suggest that normalized dipole power of TE (TM) polarization is enhanced (inhibited) in the DUV range by coupling with in-plane substrate localized surface plasmon (LSP) mode from Al/Al2O3 core-shell nanoparticle (NP). It is found that normalized upward extraction power for both polarizations can also be significantly increased by scattering effect when photons and excitons coupling with in-plane air LSP mode induced on the NP; thus, the light extraction efficiency (LEE) can be substantially enhanced. The depth d between quantum well (QW) and NP and NP size have a remarkable influence on LSP resonance wavelength. Through careful regulation of NP size and depth d, the emission characteristics in DUV range (240–280 nm) exhibit a considerable amelioration. Keywords Localized surface plasmon . AlGaN . Light emitting diodes . Finite-difference time-domain method
Introduction AlGaN-based DUV-LEDs have extensive potential applications in UV curing, fluorescence detection, water purification, and sterilization [1–5]. However, both the internal quantum efficiency (IQE) and LEE are poor due to high threading dislocation density (TDD) of epitaxial materials and dominated TM-polarized emission in the DUV range, respectively [6–8]. For a traditional planar DUVLED, the external quantum efficiency (EQE) is generally lower than 5%, which greatly limits its practical application. Different from common blue and green LEDs with InGaN active layer, the percentage of TM polarization in AlGaN-based DUV-LED becomes dominant as Al component increases or emission wavelength decreases, since the electric field orientation of TM mode is parallel to the c-axis; hence it is extremely hard to escape from top
* Huiqing Sun [email protected] 1
Institute of Semiconductor Science and Technology, South China Normal University, Guangzhou 510631, China
2
Guangdong Provincial Engineering Technology Research Center for Low Carbon and Advanced Energy Materials, Guangzhou 510631, China
and bottom of device due to strong total internal reflection (TIR) effect. So inhibiting TM mode or increasing LEE of TM mode is critical for practical applications of DUV-LEDs. Numerous processes have been widely used to boost the LEE of DUV-LEDs such as nanowire structure, chip structure engineering, optical reflectors, photonic crystal patterns, and so on [9–13]. Nevertheless, with such techni
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