| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 105 === In this thesis, mitigating efficiency droop of a light-emitting diode (LED) through the coupling between a quantum well (QW) and a surface plasmon (SP) resonance is numerically investigated. With a metal nanostructure near a QW, through SP coupling the radiative recombination rate in the QW can be increased due to the Purcell effect. We modify the carrier-density rate equation of the so-called “ABC” model to include the Purcell effect as well as the absorption in the metal nanostructure. Furthermore, we derive the formulas for various current components, carrier density, carrier lifetime and injection efficiency.
With a properly designed metal nanostructure, an Ag nanoparticle is placed on the top surface of a thick GaN layer with an embedded thin QW layer. By varying the vertical and horizontal separations between a radiating dipole and the Ag nanoparticle, we calculate the Purcell factor and the absorption factor under various situations. With these numerical data as well as assumed maximum internal quantum efficiency (IQE) and the corresponding QW injection current of a reference LED, we can evaluate the IQE, injection efficiency, carrier density and current components of an SP-coupled LED. Numerical results show that SP coupling can enhance the radiative recombination rate and the injection efficiency. At the same time, both the carrier density in the QW and Auger recombination rate are reduced. As a result, the emission efficiency of either blue or green LEDs can be enhanced and efficiency droop mitigated through SP coupling.
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