Experiment Of The Nitride LEDs With Surface 2-D Photonic Crystals

The photonic crystal?PCs?was considered to be an effective method to improve the light output efficiency?LOE?of GaN-based LED.So it has become one of the hot spots of LED.Therefore,it was of great value to study the mechanism of the effect of the surface PCs structure on the LO E of LED,and to fabricate the LED with the high LOE.The LED with different surface 2-D PCs was simulated by using the FDTD.It was found that when the duty ratio,the period and the height of PCs was in the range of 0.5 0.7,500 800 nm and 80 160 nm,respectively.The LO E of LED could be improved more effectively.On the basis of this,the commom LED?CLED?with different surface 2-D SiO₂ PCs structure was fabricated by nanoimprint lithography and LED chip preparation equipment.Then,the LED was tested.The results showed that the 2-D SiO₂ PCs structure could improve the output power?LOP?of LED.The LED with the square lattice SiO₂ PCs,which period was 600 nm,had a maximum LOP.Which was 14.95% @20mA higher than that of the LED without surface microstructure.In addition,the chip with the surface 2-D SiO₂ PCs structure was fabricated on the ultraviolet?UV?,blue and green LED epitaxial wafers by using the preparation process,respectively.The experimental results showed that the surface SiO₂ PCs structure could improve the LO E of UV and green LED more effectively than that of the LED without surface microstructure.It increased by 27.51% and 32.63% @20mA,respectively.And the square lattice PCs could improve the LOE of the LED more effectively than that of the hexagonal lattic PCs.From the far field radiation pattern of the LEDs,it was found that the radiation energy of the green LED with the square lattic PCs was the largest.The flip-chip thin-film LED?FC-TFLED?model was established by using the FDTD.The results showed that the higher LOE of FC-TFLED could be obtained with a short cavity length,suitable p-GaN layer thickness and PCs structure.After optimization,the LO E of FC-TFLED with the surface PCs reached 53.0%.Which is 56% and 103.8% higher than that of the non-surface microstructure and the unoptimized cavity length,respectively.Meanwhile,the surface PCs did not change the resonant cavity effect of FC-TFLED.