ABSTRACT
Out-of-plane lattice plasmons (OLPs) show great potential in realizing high-quality factors due to the strong interparticle coupling. However, the strict conditions of oblique incidence bring challenges to experimental observation. This Letter proposes a new, to the best of our knowledge, mechanism to generate OLPs: through near-field coupling. Notably, with specially designed nanostructure dislocation, the strongest OLP can be achieved at normal incidence. The direction of energy flux of the OLPs is mainly determined by the wave vectors of Rayleigh anomalies. We further found that the OLP exhibits symmetry-protected bound states in the continuum characteristic, which explains the failure of previously reported symmetric structures to excite OLPs at normal incidence. Our work extends the understanding of the OLP and brings benefit to promote the flexible design of functional plasmonic devices.
ABSTRACT
Tamm plasmons (TPs), whose plasmon modes are confined at the Bragg reflector/metal interface due to the photonic stopband of the reflector and the negative dielectric constant of the metal, exhibit many advantages over the conventional surface plasmons (SPs) and potential applications in sensors, filters, optical circuits and light-emitting devices. In this paper, a TP-cavity structure has been proposed for accelerating the light emission and alleviating the large metal loss, which is hopeful for solving the efficiency droop and "green gap" problems in InGaN green light-emitting diodes (LEDs). The light emission performance of TP-cavity LEDs was systematically investigated based on transfer matrix and finite-difference time domain methods. Purcell factor (Fp) and light extraction efficiency (LEE) were both remarkably enhanced, which would be attributed to the presence of the TP and/or SP modes induced by the TP-cavity structure. In addition, two important factors including the thicknesses of the top Ag film and medium layer were investigated in detail and taken into account for the balance between the Fp and the LEE. Finally, light emission intensity was significantly enhanced for the TP-cavity green LEDs after the structure optimization as compared to the conventional green LEDs.