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 (F_p) 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 F_p 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.

We propose a unidirectional surface plasmon polariton (SPP) launcher with high coupling efficiency and long propagation length. The structure consists of a metallic slanted grating and a metal film that are separated by a SiO₂ layer on a quartz substrate. By inserting the SiO₂ layer, strong interaction between the metal grating and metal film can significantly increase the conversion of incident light into SPPs. Meanwhile, due to the characteristics of the smooth interface between metal film and substrate, the dissipation of SPP originating from the propagation process will be remarkably reduced. Numerical simulations show that this structure with 11 grating periods will obtain high contrast and efficiency of launching. Compared with the rough metal–quartz interface, the smooth one can improve the efficiency of light conversion to SPPs by more than 22.6% and extend the propagating distance by approximately 158%.

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 (F_P) 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.

We investigate a method to improve the efficiency of green InGaN light-emitting diodes (LEDs) using various metal-doped indium tin oxide (ITO) transparent contact layers. The resistance and transmittance of metal-doped ITO with different metal thicknesses and different rapid thermal annealing conditions were studied and analyzed systematically. It is found that extinction coefficient and surface roughness of ITO layer are distinctly reduced by doping suitable metal and annealing in a mixture of N2/O2 (200:35) ambient at 600 °C for 3 min. In addition, it is useful to decrease the sheet resistance and provide more uniform current distribution by using the metal-doped ITO. Compared with conventional green LEDs with 80-nm ITO layer, there are an 18.9% increase in light-output power and a 1.5 V decrease in forward voltage at 120 mA for the green LEDs with 3-nm Al-doped ITO layer.