Research On Structure Design And Characteristics Of GaN-Based Micro LEDs

In this thesis,due to the low power consumption,long lifetime,short response time and other outstanding characteristics,micro LEDs and their arrays have a wide range of application potential in display,communication,medical treatment and other fields,such as display backlight units,self-emissive display units,and emitting light source of visible light communication system,etc.There is an urgent need to design and prepare high-efficiency and high-performance micro LEDs to meet the requirements.In view of the influencing factors of light efficiency and-3d B bandwidth characteristics of micro LED,simulation analysis and experimental research on device structure,sidewall structure and its integration were carried out from the perspective of improving light efficiency.At the same time,p-electrode structure and device connection mode were optimized based on-3d B bandwidth.The main contents are as follows:1.The characteristics and principles of current spreading inside the LED have been discussed.The Monte Carlo ray-tracing simulation method was used to simulate the relationship between chip structure and photon escape.Combined with the multiphysics coupling finite element method,the analysis of the influence of the chip structure on the uniformity of the current density distribution was supplemented.The influence of the chip structure on the characteristics of the micro LED were studied through experimental comparison.The results show that,compared with the micro LED with chip structure of circular-type,the light output power of the micro LED with chip structure of pentagon-type is increased by 6.08% due to the reduction of the total internal reflection effect.In addition,the relationship between the size of the micro LED and its injection saturation current density and capacitance is compared and analyzed.2.The influence of various sidewall structures on the light extraction efficiency of micro LEDs were analyzed by using the finite difference time domain method.Based on the inductively coupled plasma(ICP)etching technology,the influence of the types and sizes of sidewall structures on the current-voltage characteristics,light output power,wall-plug efficiency of the micro LEDs were compared and studied.The results show that,compared with the flat sidewall structure,the concave-convex circular composite structure sidewalls was more conducive to the escape of photons and the improvement of light efficiency of the micro LEDs.When the radius of the convex-circle is 2 ?m,the light output power achieves the maximum value,which is 7.2% higher than that of the micro LED with flat sidewall structure.3.The influence of snowflake-shaped p-electrode structure with different number of branches on the current density distribution of micro LEDs were analyzed by using the multiphysics coupling finite element simulation method.The influence of the hybrid structure with different sidewall structures and different p-electrode patterns on its current-voltage characteristics,light output power,current distribution and other properties were compared and studied.A hybrid structure integrating composite structure sidewall and snowflake p-electrode pattern was designed on the micro LEDs.Among them,the composite structure sidewall reduces the total internal reflection at the GaN/air interface,and the snowflake p-electrode structure improves the uniformity of current distribution,thereby significantly improving the optical performance of the micro LEDs.And an integrated hybrid structure technology for improving the light output power is obtained.4.Using multiphysics simulation method,the relationship between the area,branch number,shape of the p-electrode and current density distribution of micro LEDs was explored.The characteristics of the current spreading inside the LED is discussed.And the effects of branch numbers and branch shapes of the p-electrode structure on the photoelectric characteristics of micro LEDs are comparatively studied.By optimizing the number and shape of the branches of the p-electrode structure,the uniformity of the current distribution inside the micro LED can be improved,thereby improving the photoelectric performance.In addition,a comparative analysis of its influence on the modulation characteristics of micro LED is conducted,and it is found that the improved current distribution can not only increase the injection saturation current density of the device,but also reduce the series resistance,thereby increasing the-3 d B bandwidth of the micro LED.Compared with the micro LED using the disk p-electrode structure,the saturated light output power and the-3 d B bandwidth of the micro LED using the 6-branch spiral p-electrode structure have been increased by39.48% and 76.61%,respectively.5.By adopting a micro LED array with a parallel connection structure to increase the light output power,and the influence of the pixel number and the pixel pitch on its photoelectric performance or modulation characteristics is explored.The results show that by changing the number of pixels connected in parallel,the light output power of the micro LED arrays have improved to varying degrees due to the increase in the area of the active area.The corresponding-3 d B bandwidth exhibit similar characteristics at the same current density due to the complementary effects of the increased capacitance and the decreased dynamic resistance.In addition,the pixel pitch has a slight influence on the optical performance of the micro LED arrays without the introduction of isolation grooves,but it is almost negligible.