Study on improving the extraction efficiency of blue light LED by metal gratings

In order to improve the light extraction efficiency of light-emitting diodes (LED), the influences of different grating shapes on the light extraction efficiency of LED were compared.The flip chip LEDs, which was integrated with rectangle, isosceles triangle and isosceles trapezoidal grating, were optimized by rigorous coupled wave method to make the transmittance of the light-exiting surface best. Finite-difference time-domain method was used to simulate the efficiency of light extraction. After simulation calculation and theoretical analysis, the optimal grating parameters (grating duty ratio f, grating period p, grating thickness h) and transition layer thickness d of the LEDs with 3 different structures can be obtained: f=0.35, p=150nm, h=80nm, d=190nm; f=0.45, p=175nm, h=80nm, d=190nm; f=0.7, p=150nm, h=80nm, d=190nm. The results show that, in the wavelength of 0.4μm to 0.5μm, the flip-chip LED of the rectangular grating and the flip-chip LED of the isosceles triangle grating have the same transmittance.The flip-chip LED of The isosceles trapezoidal grating has the lowest transmittance. Because of the lowest transmittance, the light extraction efficiency of the flip-chip LED of the isosceles trapezoidal grating is lower and the highest is only 58.07%. The optical extraction efficiency of the flip-chip LED of the isosceles triangle grating with special grating shape can reach 77.75%.The study can provide theoretical guidance for manufacturing high light extraction efficiency LED in the future.