| The development of modem optics and electronics technology has shown great improvement, especially the research on sub-wavelength structure has broken the bottle-neck of improvement of LED light extraction efficiency (LEE), which has given the brand new idea for national energy saving and emission reduction.The study of basic physics problems such as energy transmission, waveguide mode and the near and far field energy distribution characteristics in the nanostructures electromagnetic field, both with the deeply understanding of the waveguide mode, energy transmission, waveguide coupling physical laws of the electromagnetic field and the surface nanostructure interaction, can provide theory guiding for improving LED light extraction efficiency with surface nanostructure.Around problems above, for improving the luminous efficiency, this dissertation studied those problems by using computer simulation and other means, focused on the following issues closely around the surface nanostructure and GaN-based blue light emitting diodes.Through finite difference time domain method (FDTD), realize the numerical simulation of surface nanometer structure of light emitting diode.Deriving the basic physical properties from different model of regional nanostructure interaction with electromagnetic field through the Maxwell equations.Exploring the way of improving light extraction efficiency of LED and the related theoretical basis through the study of light emitting principle of LED and the energy conversion process between the light and electricity.By comparing and analyzing varied surface nano structure, different characters and benefits for anti-reflection of surface structure have been shown.By all kinds of material and electromagnetic parameters numerical simulation on nanometer microlens structure, the regulation of surface nanometer microlens acting on enhancing the LEE of LED has been achieved.Combined the regulation of surface microlens structure on improving the LEE with the waveguide model analysis method, the parameters of GaN-based LED structure has been optimized.This dissertation is mainly studying on the nanometer micro structure working principle on improving the LEE and the positive effects on promoting the efficiency of converting electricity to light. Closely around the energy-saving and emission-reduction premise, the subwavelength microlens structure on the small LED surface has been constructed. Further exploring the improvement method on promoting the LEE of GaN-based LED, which will offer the valuable experience for experiment in the lab or large scale commercial production is proposed. Comparing and analyzing multiple methods with basic principle and experiment effects on improving the LEE of GaN-based LED, including flip-chip structure, surface pattern, photon crystal and so on. The pros and cons of varied methods have been comprehensive demonstrated on fabrication techniques and benefit cost anaysis.According to these research purpose and contents, the innovations of this dissertation are covering the four aspects:1. The numerical simulation of surface micro structure on LED has been achieved by the3D GaN-based LED model. According to varied period and structure GaN-based LED of the luminescence characteristics and field distribution characteristics, the concept of equivalent refractive index has been introduced, and the optical transmission mode has been analyzed, at last, the correctness of the method is verified.2. In order to verifying the influence of the efficiency of GaN based LED of same structure under different materials, varied refractive index waveguide material such as GaN, ZnO, SiO2, PS have been first introduced in the same surface microstructure. Periodic effect regulation of varied material acting on the LEE of GaN-based LED has been obtained in subwavelength field.3. Based on the previous work, numerical simulation by finite difference time domain method, the significant effect of surface micro structure raised LEE of GaN based LED has been determined. The various parameters of nano microlens hexagonal array have ultimately been optimized by defining the depth with variable angle and then defining radius with changing relative depth. At last, the light extraction efficiency of the final model can reach more than five times enhancement than that of those planar ordinary LED.This work in this dissertation is supported by the National Natural Science Foundation of China, the National Basic Program of China (973program). Through the analysis of the microlens structure in sub-wavelength scale and the waveguide mode theory in light emitting diode, the theory of light in the diode waveguide material and practice of the photoelectric conversion have been explored. New ideas and direction have been provided for developing a high-tech, technology-breakthrough materials and high brightness blue light emitting diodes, while theoretical support and innovation have also been provided for high efficiency LED by using the surface microlens structure. |
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