Abstract
Planar, nanopillar and Al nanosphere structure AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) were numerically investigated via a three-dimensional finite difference time domain (3D FDTD) method. The three types of DUV-LEDs were compared and analyzed in terms of light extraction efficiency (LEE), Purcell factor (FP) and modulation bandwidth. The results showed that nanopillar structure DUV-LEDs with optimal nanopillar height, width and spacing can enhance transverse electric (TE)-polarized LEE to 39.7% and transverse magnetic (TM)-polarized LEE to 4.4%. The remarkable improvement was mainly due to the increased scattering effect, decreased absorption of the p-GaN layer and total internal reflection (TIR) effect. After adopting the Al nanospheres, the TE-polarized modulation bandwidth was increased by 71 MHz and the TM-polarized LEE was enhanced approximately 4.3-fold as compared to the nanopillar LED structure, while the Al nanosphere diameter was 120 nm. The reasons for promotion are mainly attributed to the coupling behavior of diploe and localized surface plasmon induced by Al nanospheres. The designed structures provide a meaningful solution for realization of high-efficiency DUV-LEDs.
Highlights
Academic Editors: Degang Zhao andIn recent years, AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) have been greatly developed because of their wide-ranging applications, including water and air purification [1], disinfection [2] and DUV communications [3]
external quantum efficiency (EQE) is the product of two independent factors: the internal quantum efficiency (IQE) and the light extraction efficiency (LEE)
As the Al component in AlGaN-based quantum gradually increases [7], transverse magnetic (TM) polarization of DUV-LEDs accounts for the main part of transverse electric (TE) polarization
Summary
AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) have been greatly developed because of their wide-ranging applications, including water and air purification [1], disinfection [2] and DUV communications [3]. Improving LEE of DUV-LEDs is necessary, and several strategies have been proposed including nanowire structure [8], patterned sapphire substrates [9], surface roughing [10] and photonic crystal patterns [11] Another effective way that placing metal nanoparticles on the p-GaN contact layer to stimulate localized surface plasmons (LSPs) coupling behavior is beneficial is that it enhances spontaneous emission rate and light extraction [12,13,14]. For the Al nanosphere structure, QW-LSP coupling effect induced by Al nanospheres have intention of improving the overall LEE, FP and LEE of TE and TM-polarized DUV-LEDs. the modulation bandwidths of planar and proposed structures are theoretically calculated and demonstrated. The optical characteristics, such as LEE, FP and modulation bandwidth, are carefully discussed for nanopillar and Al nanosphere structure DUV-LEDs
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