Besides lighting, LEDs can be used for indoor data transmission. Therefore, a large modulation bandwidth becomes an important target in the development of visible LED. In this regard, enhancing the radiative recombination rate of carriers in the quantum wells of an LED is a useful method since the modulation bandwidth of an LED is related to the carrier decay rate besides the device RC time constant To increase the carrier decay rate in an LED without sacrificing its output power, the technique of surface plasmon (SP) coupling in an LED is useful. In this paper, the increases of modulation bandwidth by reducing mesa size, decreasing active layer thickness, and inducing SP coupling in blue- and green-emitting 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 microns in radius, SP coupling results in a modulation bandwidth of 528.8 MHz, which is believed to be the record-high level. 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.
Chun-Han Lin, Charng-Gan Tu, Yu-Feng Yao, Sheng-Hung Chen, Chia-Ying Su, Hao-Tsung Chen, Yean-Woei Kiang, and Chih-Chung Yang, "High modulation bandwidth of a light-emitting diode with surface plasmon coupling (Conference Presentation)," Proc. SPIE 10124, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXI, 101240M (Presented at SPIE OPTO: January 31, 2017; Published: 20 April 2017); https://doi.org/10.1117/12.2249539.5398643882001.
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