Study On Light Extraction Efficiency Of GaN Led

Group ? nitrides have made a series of breakthroughs in the technical application of red,yellow,blue,and green light-emitting diodes and laser diodes,making GaN LEDs basically complete the primary color spectrum.With the realization of higher brightness and efficiency lighting technology,LED began to enter the lighting market widely,and has gradually occupied its dominant position in most lighting applications.Until recent years,the key performance of blue LEDs such as internal quantum efficiency has been almost raised to the limit,but its external quantum efficiency is much lower than the internal quantum efficiency,making LED light extraction efficiency has become a hot spot of technical research in recent years.High-power LED has entered the field of vision of researchers because the characteristics of small size,low voltage,long life,high electro-optical conversion efficiency,fast response speed,energy saving,environmental protection and so on.It has also entered the field of vision of researchers.However,due to the short period of time in which domestic research on high-power LEDs has actually begun,there are still some shortcomings in structural design and process preparation.On the one hand,due to the high refractive index between the ?-nitride layers,there is a non-negligible internal reflection inside the LED chip;therefore,reducing the optical path length inside the LED chip and minimizing the internal reflection improves the efficiency.The essential.On the other hand,the light extraction efficiency of an LED chip also depends on the structure design of the chip;extracting a large number of photons from the LED chip is the basic premise of an efficient optoelectronic device.Because the materials used to prepare semiconductor devices are usually much larger than the refractive index of air,a significant portion of the light generated travels along the surface with total internal reflection.At the same time,the current problem of device failure due to poor heat dissipation in commercial high-power LEDs has not been well resolved.Therefore,high-power LEDs on the market are generally 1W and 2W,and 5W and 10 W are rarely used.At the same time,the current problem of device failure due to poor heat dissipation in commercial high-power LEDs has not been well resolved.Therefore,high-power LEDs on the market are generally 1W and 2W,and 5W and 10 W are rarely used.Therefore,the research on the light extraction efficiency of high-power LEDs is of great significance.This paper mainly solves the problems of light extraction efficiency and current crowding of high-power LEDs.The structure and layout of high-power LEDs under different mesa widths with an injection current of 350 m A are designed,and the structure of our design is simulated.The method of how to increase the optical output power of high-power LEDs and how to effectively reduce the current crowding problem of high-power LEDs under high current injection are studied,thereby improving the heat uniform distribution of the devices.We have optimized the key manufacturing process of high-power LEDs and prepared high-power LED devices with interdigitated structures(both comb-shaped mesas and interdigitated electrodes).The main factors affecting the electrical,optical and thermal performance of high-power LEDs are analyzed.The main research contents are as follows:(1)First,using the MOCVD epitaxial growth equipment,the structure of the GaN-based LED was epitaxial on the sapphire substrate.Secondly,using FIB sample preparation,and analyzing the structure and material thickness of the epitaxial wafer through transmission electron microscope and other testing equipments,the material thickness of each layer structure such as buffer layer,n-GaN,MQWs,p-GaN,etc.And compared with the sample structure we designed.Through the Hall test,the concentration of Mg in p-GaN and Si in n-GaN were obtained.Finally,an experimental research program suitable for studying the electrical,optical,and thermal performance of high-power LEDs was developed.(2)Designed the layout of high-power LEDs under different table widths,mainly including traditional large-size structures and three comb-shaped LEDs under different table widths.According to the device size of high-power LED,the width and number of mesa are determined,and the width and number of nand p-electrodes are further determined.According to the traditional preparation process,the layout of each step of the high-power LED is determined.Through FDTD simulation,the structures we have designed was simulated,and the effect of different mesa widths on the LED light extraction efficiency was studied,and a comb-shaped mesa structure LED that was conducive to light extraction was obtained.(3)Optimized the key preparation process of LED in large size.First,by comparing the problems existing in both wet etching of ITO and IBE dry etching of ITO,a suitable etching process was determined.The factors affecting the ICP etching rate and morphology were studied,and the appropriate etching conditions were selected.Secondly,the transmission line model was used to perform orthogonal experiments on the annealing conditions of the interdigitated electrode metal,and the annealing conditions with the best luminous performance of the device under the ohmic contact condition were obtained.(4)The traditional structure of the high-power LED and the interdigitated structure of the chip were prepared under the same process conditions.The electrical and optical characteristics of the LED under different structures and processes and the thermal characteristics of the chip were tested and analyzed.By comparing the LED light extraction efficiency under different structures,the experimental results are consistent with our previous simulation results.Through the experimental results,it is found that this kind of LED with an interdigitated structure is not only helpful to improve the light extraction efficiency but also to improve the current expansion performance.