Study On The Optoelectrical Properties Of GaN-based LEDs During Short-term Current-stress Aging

Being a great challenge,solutions to luminous efficiency attenuation and device aging of blue and green LEDs under high-current driving condition are still of paramount importance.In this work,we study the light efficiency attenuation GaN-based blue and green LEDs during a short-term aging via various detection methods.We present mechanisms related to the photoelectric properties of GaN-based LEDs from various aspects.The details are as follows:1.We studied the luminous efficiency Droop effect of blue and green LED under cryogenic temperature and low current combined with short-term aging.To date,the commercial prospect of LEDs is greatly limited by the Droop effect of LEDs,especially that high-power LEDs that operate under the current in which luminous efficiency Droop effect occurs.Although much progress has been achieved on the luminous efficiency Droop effect at normal temperature and high current,it is still controversial that the cause of the decline for luminous efficiency under large current.In this work,we conducted the LEDs test under vacuum-cryogenic temperature environment,and the study showed that the luminous efficiency of blue and green light LEDs would decrease under cryogenic temperature and low current as the current density increase,however,it would not happen at normal temperature.According to previous studies,this phenomenon is due to the nonuniform injection of holes under cryogenic temperature and low current.Compared with the difference of the In component between the blue and green LEDs,as well as the experimental phenomenon and the test results after the short term aging of green LED,we found that the point defect would generate the energy potential well in the quantum well and act as non-radiational center,thus impacting on the luminous efficiency of blue and green LEDs under cryogenic temperature.In this article,we built a physical model to illustrate the influence mechanism of point defects on the external quantum efficiency of blue and green LEDs under different current excitation densities and temperatures.2.We studied the evolution of optical performance of green LED during short-term aging process by means of the microscopic hyperspectral image technology.In this study,through the microscopic hyperspectral image technology we analyze the evolution of the spatially-resolved optical performance of green LED surface,during the short-term aging process.The experimental data illustrate lots of small bright spots on the surface of the chip before aging,most of which disappear after short-term aging,accompanied by reduction of the overall luminescence intensity of the.The peak wavelength shifts towards blue end within 1 hour,and then turn to red-shift for the rest of aging.These phenomena are related to the evolution of defects and In components in green LED during aging process.In addition,the peak photon energy and luminous intensity in the region near the cathode are significantly higher than those in the remote regions,under low current density.As the current density increases,these distributions become uniform.Based on the comparative analysis of experimental data,we believe that this is related to the inhomogeneous currents distribution under low current excitation density.In this study,we have successfully applied microscopic hyperspectral image technology to LED detection.These studies have laid the foundation for the research of Micro-LED display in our future works.