Research On GaN-based Photonic Crystal LED

Visible light communication has the advantages of good confidentiality,high transmission rate,no electromagnetic radiation,environmental protection and security.It can be used as a communication scheme to alleviate the shortage of spectrum resources,and it is the frontier technology and hot spot of current research.GaN-based LED is the key device for visible light communication.It has been commercialized in the lighting field.However,the narrow bandwidth of commercial LED chips limits the overall bandwidth of the visible light communication system.Photonic crystal structure can affect the photon lifetime and photon propagation in space,thus changing the bandwidth of LED chip and light extraction efficiency.Therefore,it is of great significance to study the photonic crystal LED.In the paper,the Purcell factor and light extraction efficiency of photonic crystal LED and flip-chip LED are studied by FDTD Solutions software in detail.The Purcell factor and light extraction efficiency of LED chip are improved by optimizing the parameters of photonic crystal period,duty cycle and height.The simulation results show that the Purcell factor and the light extraction efficiency of photonic crystal formal LED are inversely correlated,while the Purcell factor and light extraction efficiency of the photonic crystal Flip-chip LED show a positive correlation trend.When photonic crystal flip-chip LED has a period of 400 nm,a duty ratio of 0.3,and a height of 400 nm,its Purcell factor is 1.81,which is 37% higher than that of formal LED.Its light extraction efficiency is 68%,which is 32.3% higher than that of flat plate LED.Compared with the normal structure,photonic crystal flip-chip LED can improve efficiency and Purcell factor od the chip.Photonic crystal LED chips with a period of 400nm-800 nm were fabricated by nanoimprint technique.Fluorescence lifetime and Raman measurements were performed.The photonic crystal chips were characterized by good morphology,uniform pattern distribution and uniform etching depth.The effect of photonic crystal structure on photonic lifetime and stress is discussed.The results show that the peak value of Raman spectrum of photonic crystal LED is higher than that of flat plate LED.The shift of the peak position of the mode signal of InGaN material indicates that the stress of the epitaxial layer is released by the photonic crystal structure.Fluorescence lifetime test shows that the photon lifetime of the sample etched with photonic crystal structure is significantly decreased and the Purcell factor increases obviously,which is consistent with the simulation results.The photonic crystal LED with periodic 400nm-tetragonal array is optimal,and its photonic lifetime is only 0.621 ns.