Research On GaN-Based LED With High Luminous Efficiency And High Modulation Bandwidth Based On Surface Plasmon Enhancement Effect

Gallium Nitride(GaN)based light emitting diodes(LEDs)have the advantages of the small size,high efficiency,low power consumption,fast response speed,long lifetime,high reliability and others,which can simultaneously achieve lighting and communication.However,due to the limitation of the semiconductor material quality,the relatively small total reflection critical angle of the GaN-air interface(about 23.5°)and the heat dissipation performance of LEDs,the luminous efficiency and modulation bandwidth of LEDs are still not high enough and can still be improved.Based on this,the purpose of this paper is to design the GaN-based LEDs with high luminous efficiency and high modulation bandwidth.Since the luminous efficiency of LED is mainly determined by its internal quantum efficiency(IQE)and light extraction efficiency(LEE),its modulation bandwidth is mainly determined by its RC time constant and carrier recombination lifetime,and improving the IQE and heat dissipation performance of LED can reduce its carrier recombination lifetime.Therefore,the metal Ag is used to induce surface plasmons(SPs)and improve the IQE of LEDs.The surface roughening,flip-chip and patterned substrate technologies are used to improve the LEE of LEDs.The diamond heat dissipation structure is used to improve the heat dissipation performance and the upper limit of the injected current density of LEDs.The main contents of this paper are as follows:(1)A high luminous efficiency GaN-based LED is designed.The periodic Ag gratings are used to induce SPs,which can be coupled with quantum wells(QWs)to improve IQE.The indium tin oxide(ITO)triangular grating is used to improve LEE.The ITO-SiO₂quasi-symmetrical waveguide structure is used to improve the SPs extraction efficiency and LEE.The Ag/SiO₂ core-shell nanoparticles are used to reduce the absorption loss caused by the direct contact between Ag and p-GaN.The radio frequency(RF)module of the COMSOL software is used for simulation calculation and parameter optimization of the designed structure.The results show that the designed novel LED has high luminous efficiency,and its maximum radiated intensity is about 58.59 times that of the traditional LEDs at the wavelength of 460nm.This research provides important guiding significance for the development of GaN-based LEDs with high luminescence performance.(2)A high modulation bandwidth GaN-based LED is designed.The periodic Ag nanopillar array is used to induce SPs,which can be coupled with QWs to improve IQE.The periodic diamond array is used to improve the heat dissipation performance of the chip,thereby increasing the upper limit of the injection current density.The RF module and heat transfer module of the COMSOL software are used for simulation calculation and parameter optimization of the designed structure.The results show that the designed novel LED has high modulation bandwidth,the maximum average electric field mode of the novel LED is about 27 times that of the traditional LED at the wavelength of 450nm,the upper limit of the injection current density is 2.182×10⁴Acm^-2,and the injection current density under the ideal working conditions is 9.697×10³Acm^-2.This research provides important guiding significance for the development of high modulation bandwidth GaN-based LEDs,and provides favorable conditions for the development of VLC systems with high transmission rate.(3)A partitioned flip-chip GaN-based LED with high luminous efficiency and high modulation bandwidth is designed.The periodic Ag nanopillar array is used to induce SPs,which can be coupled with QWs to improve IQE.The flip-chip structure and patterned substrate technology are used to improve LEE.Diamond is embedded into the LED chip and a diamond heat sink is welded on the metal reflective layer to improve the heat dissipation performance and the upper limit of the injected current density.The RF module and heat transfer module of the COMSOL software are used for simulation calculation and parameter optimization of the designed structure.The results show that the designed partitioned flip-chip LED has high luminous efficiency and modulation bandwidth,its radiated intensity is 15.44 times that of the face-up chip,the upper limit of the injection current density is up to 4.89×10⁴Acm^-2,and the injection current density under the ideal working conditions is up to 1.78×10⁴Acm^-2.The designed novel GaN-based LED can be applied to some special occasions such as mines,aerospace and underwater submarines.