Design And Fabrication Of Vertical Structure LED Chip For Visible Light Communication

Visible light communication technology,as an emerging wireless communication method,is expected to alleviate the spectrum crisis caused by the rapid growth of global data demand.LED(Light-Emitting Diode)devices are considered to be one of the most ideal light sources for visible light communication systems because of their fast response time,excellent optoelectronic performance and low cost.Currently,commercial lighting LEDs often limit the further development of visible light communication due to low modulation bandwidth.Therefore,it is of great importance to develop LED chips with high bandwidth and excellent optoelectronic performance for visible light communication.Compared with the traditional lateral and flip-chip structures,vertical structure LED chips have the advantages of high power and high luminous efficiency.Therefore,this paper conducts a study based on the epitaxial structure,electrode structure and array technology of Ga N-based vertical structure LED chips.1.An epitaxial structure with a small number of MQWs and a thin EBL(Electron Blocking Layer)was designed with the guidance of APSYS software,which improved the 3 d B bandwidth of LED.The LED epitaxial structure is modeled by APSYS finite element simulation software.And the ABCD model,which complements the traditional ABC model describing the carrier recombination mechanism,is used to analyze the effects of the number of LED quantum well periods and the EBL thickness on the bandwidth factor.The simulation results show that a small number of quantum well periods and a thin EBL layer can improve the percentages of auger recombination or electron leakages,which are beneficial to the preparation of high-bandwidth LED epitaxial structures.LED epitaxial wafers with a quantum well period number of 4 and an EBL thickness of 7 nm were grown by MOCVD(Metal-Organic Chemical Vapor Deposition).The prepared LED devices with dimensions of 800μm×800μm showed a 33%bandwidth enhancement at 1000 m A injecting current.2.Vertical structure micro-LED devices with via-hole structure for visible light communication were designed and prepared.The differences in optoelectronic performance as well as communication performance between the conventional linear vertical structure and the new vertical structure with via-hole electrode were then compared,demonstrating the advantages of the via-hole structure in preparing high current injection density LED devices due to its better light distribution and current extension capability.A variety of LEDs with via-hole structure ranging in size from 500μm to 30μm were also prepared,and the test results showed that the smaller size LEDs can withstand higher current densities and also achieve higher bandwidths,although the light output power is lower.LED devices with a size of 30μm can achieve a 3 d B bandwidth of 256 MHz at a high current injection density of 15.8 k A/cm~2.3.The effect of parallel array technology on the optoelectronic performance and communication performance of micro-LED devices with via-hole structure was investigated.Parallel micro-LED array chips from 1×1 to 6×6 with via-hole structure in diameters of 30μm and 50μm were prepared.The optoelectronic and communication performance of the array chips were tested and analyzed,and it was found that the RC time constant of the devices decreases as the number of arrays increases,and the light output power of the LEDs under the same current density undergoes a simultaneous increase with the bandwidth.However,the current density that the LED device can withstand decreases as the number of arrays increases.Under the combined effect of RC time constant and withstand current density,the 30μm 3×3array LED can reach the highest 606 MHz bandwidth,while the light output power can reach15.0 m W.The aging test results show that:after aging with small injection current density,the aging damage of the array LED device is smaller,so in practical application scenarios,the LED array chip should be chosen the appropriate operating current to improve the stability of the device and the system.