Study Of Improving Light-emitting Efficiency Of GaN Based LED By Surface Micro Structures

Facing the increasingly serious energy crisis, all the countries around the world have taken various measures to develop the energy-saving methods. LED which has the advantages of long service life, high energy conversion efficiency, fast response speed and so on, has gained more and more attention in recent years. Among the performance indexs of the LED, the external quantum efficiency is a very important one, and it is decided by two factors (inner quantum efficiency and the light extraction efficiency). Under the background of the internal quantum efficiency can reach more than80%, to enhance the LED light extraction efficiency has become a pressing matter of the moment, and kinds of studies of light extraction efficiency have also carried out like a raging fire.Nowadsys lots of methods for light extraction efficiency enhancement has emerged, such as the transparent substrate, metal film reflection technology, surface micro structure technology and flip chip technology. Among them the method of surface micro structure was especially paied widly attention, and the related experiments have already achieved remarkable results. However, most of the research is based in the experiment, and the importance of computer simulation doesn’t get a enough value. Computer simulation can help a lot in the study of experimental phenomena and the optimized structure parameters, which can saving a lot of experimental preparation time and material. In addition, the simulation methods in the current mainstream include finite element method, the finite difference time domain method and the ray tracing method. However, different algorithms have different advantages and disadvantages. The micro nano composite structure which appeared in the past few years is more complex, so that it is difficult to have an effective simulation with one single algorithm. So there is an urgent need to find a reasonable solution for the composite structure.This paper is based on the FDTD and the ray tracing method algorithm, and its aim is to explore the influence of different surface micro arrays on light extraction efficiency of LED. This paper briefly introduces the basic knowledge of LED development history and light-emitting principle, and the main content of this paper includes two parts:1. In order to improve the light emitting efficiency(LEE) of GaN-based blue LED, two LED models covered by ZnO nano-structures, including nano-rod and nano-cone structures, are simulated in the method of FDTD. The results of these simulations show that the light emitting efficiency of LED is varying regularly with the different nanostructures’geometric parameters (such as the period:P, the wide of bottom:W, and the length:L). We get the optimized model structure, and we can find that both ZnO nano-rod and nano-cone can bring obviously incensement on LEE. Besides, with the analysis on the variation curve, we theoretically explain the influence of ZnO nano-structure and the reason of the optimization results.2. We exployed a novel approach to calculate the LEE of micro/nano hybrid structure by combining Finite Difference Time Domain (FDTD) method and Ray Tracing Method (RTM) through the gradient refractive index layers. In this novel method, the LEE enhancement mechanism of hybrid structure can be investigated obviously. In addition, we further seek to the optimal parameters of the hybrid micro/nanorod structure, and an optimized structure with a enhancement factor of greater than95%is achieved.Through our work, some of the mechanisms of the improving LEE of LED by surface micro structure were gotten, and these results provide a theoretical reference on the practical design and optimization of highly efficient GaN-based LED.