High Modulation Bandwidth of a Light-Emitting Diode With Surface Plasmon Coupling

The enhancement of the modulation bandwidth (MB) of a light-emitting diode (LED) by reducing its mesa size, decreasing its active layer thickness, and inducing surface plasmon (SP) coupling with its quantum well (QW) is illustrated. The results are demonstrated by comparing three different LED surface structures, including bare p-GaN surface, Ga-doped ZnO current-spreading layer, and Ag nanoparticles for inducing SP coupling. In a single-QW LED with a circular mesa of 10 μm in radius, SP coupling leads to a record-high LED MB of 528.8 MHz in the visible range. A smaller RC time constant can generally lead to a higher MB. However, when the RC time constant is smaller than ~0.2 ns, its effect for increasing MB saturates. The results also confirm that the MB is essentially proportional to the square roots of carrier decay rate and injected current density.