Study On Improving Light Emitting Efficiency Of LED By Using Silver Nanodisk Array

With the advantages of saving energy, small size, high reliability, long life etc., light emitting diodes (LED) are widely used in many fields of social life. GaN-based LED could be used as illuminating source of general lighting. With the continuous development of related technologies, GaN-based LED is promised to be the right replacement of conventional light sources and the ideal choice for green lighting. However, the conventional LED has a very low emitting efficiency under the influence of the total internal reflection and Fresnel diffraction effect. Nowadays, with the development of nanotechnology, optimizing the structure of LED in nanoscale has been proved to be an effective method in theory and experiments.In the recent years, photonic crystal technology and surface plasmon technology, which have been the research focus of nano-optic field, received considerable attention by many researchers to be used in improving emitting efficiency of LED. As a periodic structure, photonic crystal fabricated in LED could convert the waveguide mode to radiation mode by grating vector. Thus the light extraction efficiency could be improved by photonic crystal. Some metallic structures could be added in LED as the generated surface plasmon polariton would couple with quantum well. As a result, spontaneous efficiency could get enhanced and the internal quantum efficiency could be improved.Based on the periodic structure and plasmonic theory, a new LED structure with silver nanodisk array embedded in the vicinity of quantum well is proposed in this paper. With the numerical analysis method, the impact to light emitting efficiency by silver nanodisk array is investigated. The detailed research work and corresponding results are as follows:1) The electromagnetic numerical simulation to LED containing metallic structures has been realized with finite-difference time-domain method and metallic dispersion data is fitted by modified Drude model.2) The LED model with silver nanodisk array embedded above quantum well is designed. Enhancement of spontaneous efficiency in the case of different parameters is calculated. Through the analysis to calculated results and near-field distribution, it could be proved that the thickness of silver nanodisk is a predominant influence in the enhancement of spontaneous efficiency while lattice constant of nanodisk array is a very slight influence factor. Furthermore, through the analysis to the model consisting by a single disk and an electric dipole, it is theoretically demonstrated that the interaction between dipole and various SPP modes could play different roles in enhancing spontaneous efficiency.3) The impact of light extraction efficiency by silver nanodisk array is calculated and analyzed. It can be found that both light extraction efficiency and internal quantum efficiency are enhanced by means of the silver nanodisk array. Moreover, the near-field distribution could indicate that localized SPP could radiate to space because of the compensation for wave vector of SPP by lattice vector of silver nanodisk array. As a result, the light extraction could be improved.The structure of silver nanodisk array embedded above quantum well shows a good prospect to improve light emitting efficiency of LED. The research work and corresponding results provide a theoretical reference on the practical design and optimization of highly efficient GaN-based LED.