| With the rapid growth of mobile communication data in recent years,traditional radio frequency communication is facing a spectrum crisis.GaN LED-based visible light communication technology is an important solution.The wide application of solid-state lighting technology(SSL)provides an unique opportunity for the development of visible light communication.All kinds of LED light sources can be used as communication hotspots.By loading the data to the LED,the optical information is transmitted through free space and then received by the photodetector to realize wireless transmission.However,the development of visible light communication technology still faces many difficulties.The limited bandwidth of commercial lighting LEDs limits the data transmission rate of the visible light communication system,and the complex LED driver circuit reduces the reliability of the visible light communication system.It is of great significance to the development of visible light communication technology by LEDs with high bandwidth,high optoelectronic properties and simple driving.Aiming at solving the above problems,this work studies the size,array,electrode structure and optoelectronic integrated devices of LEDs.The specific research contents and conclusions are as follows:First,the effect of size and array on the performance of LED was investigated.A LED epitaxial wafer with a thin MQWs structure suitable for visible light communication was grown by metal organic chemical vapor deposition(MOCVD).Then,Micro-LED chips with cross-shaped electrode structure with sizes of 15μm,30μm and 50μm were designed and fabricated.The results show that the smaller size Micro-LED can carry higher current density and has higher bandwidth characteristics.In order to further improve the optoelectronic characteristics and bandwidth characteristics,parallel array Micro-LED chips with different cell numbers were prepared.The saturated light output power of the 30μm 2×2 array chip is3.1 mW and the 3 dB bandwidth reaches 368 MHz.Then,the effect of the electrode structure of the LED on the device performance was investigated.We compared the LED’s performance of the cross-shaped electrode structure and the ring-shaped electrode structure through Silvaco Atlas software simulation and then corresponding device were prepared.Compared with the cross-shaped electrode,the ring-shaped electrode structure can effectively improve the uniformity of the current expansion in the chip,and the light output power of the LED is increased by 56.4%.Applying the ring-shaped electrode to the parallel Micro-LED array chips,the optoelectronic and bandwidth characteristics are significantly improved.The saturated light output power of the 30μm 2×2array chip reaches 7.3 mW,and at a current density of 6.67 kA/cm~2,the 3 dB bandwidth reaches 785 MHz.The quality of communication information is significantly improved in VLC system.Finally,HEMT-LED optoelectronic integrated devices were designed and fabricated.By integrating the HEMT with the LED optoelectronics,the voltage control of the LED is realized.By etching the source and drain regions and using the multi-finger gate structure,we effectively improve the current driving capability and reduce the on-resistance of the device.The integrated device shows great linearity in gate voltage modulation of LED optical output power.At a drain voltage of 10 V and gate voltage of 2 V,the current of the HEMT-LED integrated device is 221.7 mA,and the optical output power is 58.3 mW.In summary,this work proposes a high optical output power,high bandwidth Micro-LED device based on parallel array structure.By optimizing the electrode structure,the current spreading uniformity and the performance of the LED are further enhanced.Besides,the gate voltage modulation of LED is realized by HEMT-LED hybrid integrated.This thesis provides new ideas for the preparation of LED devices for VLC,and has certain guiding and reference significance for the further research and development of visible light communication technology. |
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