Optical Power Attenuation Characteristics Analysis And Application Research Of AlGaN Based 255 Nm LED

In COVID-19 era,AlGaN based deep ultraviolet light emitting diodes（UV LED）with the characteristics of energy conservation,environmental protection,safety and efficiency,low voltage and fast switching are expected to open up a new era of portable disinfection and sterilization.However,the quantum efficiency in UV LED is far lower than that in blue LED and the phenomenon of being easily affected by the environment limits the application and development of UV LED.Exploring the internal mechanism that restricts the optical power and life of UV LED is the focus of reliability analysis,and its failure mechanism is not fully understood,especially for the 255 nm LED with high Al component with the best disinfection efficiency.Up to now,there are few studies on the mechanism of optical power degradation for 255 nm LED.The main research contents and achievements of this paper are as follows:（1）We discovered that the increase in leakage current in the low forward bias region is accompanied by a decrease in apparent carrier concentration（ACD）of quantum wells near the p side during the thermal droop process at high temperature（>300 K）,indicating that the activation of thermal defects enhances the trap-assisted tunneling effect and causes the optical power to decrease more significantly at low current.Compared with room temperature,the low emission power at low temperatures is attributed to the minority trap H₁,which has an activation energy of 0.527 e V at 190 K,according to DLTS spectrum analysis.At low temperatures above 175 K,the optical power increases as the temperature rises due to enhanced hole injection.By analysis of the droop characteristics,we concluded that the activation of thermal defects is the most probable cause of high temperature thermal droop in 255 nm AlGaN quantum well light emitting diodes,whereas hole trap H₁,which is linked to gallium vacancy complexes related defects,is the most likely source of low temperature thermal droop.（2）The aging process of AlGaN based 255 nm LED with rapid life decline under constant current stress was studied by using a variety of photonic/electronic characterization methods.The change of donor concentration of the third quantum well on the p side obtained by experiment and simulation is related to the rapid decline of optical power.It is speculated that the generation of deep level related defects in the third quantum well enhances non radiative recombination,resulting in the rapid decline of optical power.（3）Taking advantage of the characteristics of AlGaN based 255 nm LED,such as small size,low opening voltage,energy conservation and environmental protection,a disinfection robot with telescopic structure is studied and designed,which can automatically move and adjust the sterilization power and sterilization time according to the distance from the object.It can also detect the distance between the surrounding human body and animals to judge the disinfection switch,so as to avoid the direct UV exposure to human being.