Abstract
The light extraction behavior of an AlGaN-based deep-ultraviolet LED covered with Al nanoparticles (NPs) is investigated by three-dimensional finite-difference time-domain simulation. For the transmission spectra of s- and p-polarizations in different emission directions, the position of maximum transmittance can be changed from (θ = 0°, λ = 273 nm) to (θ = 0°, λ = 286 nm) by increasing the diameter of Al NPs from 40 nm to 80 nm. In the direction that is greater than the critical angle, the transmittance of s-polarization is very small due to the strong absorption of Al NPs, while the transmittance spectrum of p-polarization can be observed obviously for the 80 nm Al NPs structure. For a ~284 nm AlGaN-based LED with surface plasmon (SP) coupling, although the luminous efficiency is significantly improved due to the improvement of the radiation recombination rate as compared with the conventional LED, the light extraction efficiency (LEE) is lower than 2.61% of the conventional LED without considering the lateral surface extraction and bottom reflection. The LEE is not greater than ~0.98% (~2.12%) for an SP coupling LED with 40 nm (80 nm) Al NPs. The lower LEE can be attributed to the strong absorption of Al NPs.
Highlights
Surface plasmon polaritons (SPP) exist at an interface of the metal and dielectric material, evanescently confined in the perpendicular direction [1]
For surface plasmon (SP)-lightemitting diodes (LEDs), the of Al NPs is set to 40 nm and 80 nm, s − polarization
That for SP-LED appears in the same position
Summary
Surface plasmon polaritons (SPP) exist at an interface of the metal and dielectric material, evanescently confined in the perpendicular direction [1]. The new recombination channel of dipoles can be expected to improve the emission efficiency of the emitter It has been reported in the literature that through surface plasmon (SP)–quantum well (QW) coupling, the internal quantum efficiency (IQE) of nitride lightemitting diodes (LEDs) can be significantly improved [2,3,4], and the efficiency droop can be suppressed [5]. It can be well understood that the recombination rate of the radiation dipole can be significantly improved through SP coupling, the light extraction behavior of an SP-coupled deep-ultraviolet LED is theoretically less studied [11]. The numerical results show that, compared with the conventional QW structure, the light output intensity of the SP-coupled LED structure is significantly improved, but the extraction efficiency is low without considering the lateral surface extraction and bottom reflection. The reasonable design of metal nanostructures can improve the extraction efficiency of SP-coupled LEDs
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