Beam Shaping And Light Extraction Efficiency Enhancement Of GaN-LED

Compared with the traditional light source, light emitting diode(LED) with high photoelectric conversion efficiency, good stability, long service life, no pollution, and many other advantages, become a new generation of green lighting light source. In addition, it has the advantages of small size and narrow spectrum makes it a good signal, display light source, which can be used in micro projection system, pulse ranging, etc. All the applications have higher requirements in the volume of source, light efficiency, quasi laymen and uniformity. Often using the secondary optical design for beam shaping, but this method not only increases the volume of the optical system, but also weaken the illumination intensity.For the LED light source can be directly applied in such a system, two questions need to be solved: improving the efficiency and controlling the divergence angle of LED. In the production of life, often using the LED surface roughness and other methods to increase the emergent light, and add catadioptric system outside the LED to adjust the direction of propagation of the light.However, although simple surface roughness can improve the efficiency of the light, but unable to accurately control the beam divergence angle, and that through the secondary optical design to control the divergence angle can not fundamentally improve the efficiency of the light.In this paper, it is put forward that using the sub-micron Fresnel circles realize evenly LED lighting and using sub-micron gratings structure realize collimating light. Making sub-micron Fresnel circular ring structure and grating structure on P-GaN layer, using the finite difference time domain method(FDTD) to analyze the light efficiency and divergence angle with different thickness of P-GaN, depth of structure, light wavelength and grating period. Simulation results show that in terms of uniformity, when the light wavelength is 465 nm, P-GaN layer’s thickness is 6.6microns and the depth of Fresnel circles is 0.18 microns, the light intensity is 3.1times of the original. When light intensity reduced to only 1/e of the peak, the divergence angle is 70°, and within 50° divergence angle, light intensity was homogeneous. If the wavelength is 420 nm to 495 nm range transformation, light intensity distribution basically remains unchanged, the total light intensity slightly decreased to 2.3times. In laymen terms, when the grating period is 400 nm, P-GaN layer’s thickness is 3.3microns and the structure depth is 0.1microns, the simulation results show that the light output of the far field intensity distribution changed compared with no structure, about 50% of the emergent light collected in the 14° divergence angle range.In preparation of submicron Fresnel circular ring and grating, laser direct writing and interference exposure technology are used, which can be able to quickly get the required structure. Preparation effect was observed under electron microscope, it is found that there is still an adhesion between Fresnel circular rings and the central part has a little residue, preparation effect remains to be improved. The grating stripe is straight, and can well fit the requirements of size which is required in the simulation.