Enhanced Light Extraction Efficiency Of GaN VLED With The Microstructures Arrays

The vertical structure of GaN-based LED has become a hotspot of GaN-based LED because of its good heat dissipation performance and uniform current spreading.However,the preparation process of vertical structure LED is complex and unmature.In this paper,the highpower vertical structure LEDs were obtained by Laser lift-off sapphire substrate technology and KOH wet etching while improving the critical process flow of vertical structure LED.The mechanism of improving the external quantum efficiency of this composite process was studied.The conditions of KOH wet etching were optimized and the Monte Carlo ray tracing simulation of vertical structure LED with surface preiodic microstructure was carried out to further improve the light extraction efficiency of VLED.The optical power of the vertical structure LED prepared by laser lift off patterned sapphire substrate and KOH wet etching is increased by 123.8% compared to the conventional vertical structure LED at 20 mA injection current.By analyzing the electroluminescence spectra,it was confirmed that KOH solution could improve the light extraction efficiency,while laser lift off patterned sapphire substrate could improve the light extraction efficiency and internal quantum efficiency of vertical structure LED simultaneously.At the same time,it was found that KOH surface roughening would exacerbate the decrease in external quantum efficiency,and laser lift off patterned sapphire substrate was alleviated external quantum efficiency droop by reducing the polarization field.Simulation results based on the photoelectric coupling model show that the droop of the vertical structure LED with rough surface is faster than that of the vertical structure LED with flat surface due to the exacerbation of the current crowding effect.The conditions of KOH wet etching vertical structure LED have been optimized.For the etching of plane VLED,when etching the VLED by 25% KOH at 80 ? for 9min,the maximum light output power of the VLED is increased by 164.28% under a 100 mA injection current;For the wet etching of the vertical structure LED with periodic microstucture,when etching the VLED by 10% KOH at 100? for 6min,the maximum light output power of the LED is increased by 27.98% under a 100 mA injection current.The light extraction efficiency of VLED with surface periodic microstructure was simul-ated by Monte Carlo ray tracing method.The effects of different shape periodic surface micr-ostructures on the efficiency of light extraction were studied.The composite microstructure arrays of of the spherical and hexagonal pyramid on the surface of GaN were proposed.The light extraction efficiency of vertical structure with the composite microstructure was compa-red with the vertical structure LED without the composite microstructure wai increased by 234.4%.