Enhancement of the Modulation Bandwidth of a light-emitting Diode through Surface Plasmon Coupling

The increases of modulation bandwidth by reducing mesa size, decreasing active layer thickness, and inducing surface plasmon (SP) coupling in blue- and green-emitting light-emitting diodes (LEDs) are illustrated. The results are demonstrated by comparing three different LED surface structures, including bare p-type surface, GaZnO current spreading layer, and Ag nanoparticles (NPs) for inducing SP coupling. In a single-quantum-well, blue-emitting LED with a circular mesa of 10 m in radius, SP coupling results in a modulation bandwidth of 528.8 MHz, which is believed to be the record-high level in visible range. A smaller RC time constant can lead to a higher modulation bandwidth. However, when the RC time constant is smaller than ~0.2 ns, its effect on modulation bandwidth saturates. The dependencies of modulation bandwidth on injected current density and carrier decay time confirm that the modulation bandwidth is essentially inversely proportional to a time constant, which is inversely proportional to the square-root of carrier decay rate and injected current density.