Study On The Reliability Of AlGaN-based Deep Ultraviolet Light Emitting Diodes

AlGaN-based ultraviolet light-emitting diodes(UV-LEDs),as a new generation of UV light source,with the advantages of continuous tunable wavelength,can satisfy the precision of present various fields for UV wavelength requirements.It has the advantages of energy saving,environment friendly,small size,low working voltage,low working environment requirements,the advantages of the use of high flexibility,UV-LEDs has gradually replaced the traditional mercury vapor UV light source in the market.Due to the short life span of Al Ga N-based UV LED and the continuous improvement of its performance requirements,people need to have a deeper understanding of the failure mechanism of Al Ga N-based UV LED,that is,to study its reliability.The main research contents and results of this paper are as follows:(1)Based on the deficiency of the current UV LED testing system,we have designed a set of reliability testing system for UV light emitting devices.The system meets the requirements of scientific research and testing and has good human-computer interaction.It can monitor a variety of test parameters of multiple samples in real time during aging,and has the function of automatically processing test data,The system shortens the scientific research cycle.And we can expand the program and instrument of the system to meet the needs of the gradual development of scientific research.(2)The reliability of 280 nm LED was analyzed.The result of the study shows that in the quantum well closer to the sapphire substrate,the carriers would redistribute with aging time and stress current.Stress has a significant influence on the polarization charge and quantum well doping of Al Ga N/Al Ga N heterojunction.With the decrease of lattice mismatch between the barriers,the quantum well will relax under the action of current stress,and this phenomenon is more obvious in the quantum well near the substrate.Strain relaxation may indicate a new dislocation diffusion mechanism which affects the piezoelectric polarization charge at the heterojunction.In addition,the migration and diffusion of donor also impurities with current flow.These mechanisms lead to the mass of quantum well crystals decrease under stress,resulting in the attenuation of optical power.(3)The structure of the device had been optimized,and analysed the reliability of the optimized LED.The result of the study shows that the optical power curve increases with time and can be divided into three parts: fast decline,slow rise and slow decline.This phenomenon may be caused by the related defects of Mg or the new change of polarization electric field under the new structure.