Study On Aging Mechanism Of Gan-Based Yellow LED On Silicon Substrate

After years of research and development,GaN-based LED has shown excellent photoelectric performance,and made great contributions to the cause of energy conservation and environmental protection.Nowadays,GaN-based LED have been widely used in efficient lighting systems,and there is also a great space for the development of visible light communication in the future.For lighting systems,the best technical route is multi-color LED technology.This method not only makes up for the lack of spectra,but also avoids the loss of Stokes.The roadblock of multi-color lighting is a high efficiency yellow LED.After a lot of research,the efficiency of yellow LED has been improved significantly.But multicolor LED lighting technology requires not only high efficiency yellow LED,but also a high-reliability yellow LED.Nevertheless,the research on the reliability of yellow light LED is barely and needs to be studied urgently.In this paper,the reliability and aging mechanism of yellow LED are studied and the main conclusions are as follows:1.The yellow LEDs with dominate wavelength of 561 nm were selected out and aged by increasing the current stress method.With the increase of aging time,the degree of non-radiative recombination increased,resulting in light optical power and external quantum efficiency decline obviously in the small current density.And with the current density increased,non-radiative recombination center were saturated gradually,the decline was reduced.After aging,due to the increase of defects,the degree of positive leakage increases,which leads to the red-shift of peak wavelength for the LED.Furthermore,the aging process caused the degradation in the p-side layer,and then induced the increase in the voltage difference applied to the c-plane region and side wall of V-pits.Based on the EL spectra at 100 K,this voltage change caused more holes injected into SLs via sidewall of V-pits,which means lesser current participating in radiation recombination in MQWs after aging than before.This mechanism may also work for devices at room temperatures,which needs more investigation in the future.2.Different strain relief layer structures will impact the photoelectric performance of yellow LED.Therefore,the aging experiment was carried out for two samples with different strain relief layer structure,and the difference of reliability was analyzed as well.It was found that Si doping in the strain relief layer after n-GaN will cause the decrease in depletion width,which can enhance the internal electric field and also increase the tunnelling probability of diodes.Leading to the increase of the reverse current.After aging,for the sample with Si-doped,the external quantum efficiency decreased more significantly under the small current density.And the reason is that during the aging process,there were more doping diffused into the quantum well in the Si-doped sample,resulting in a more obvious decrease in efficiency.3.In addition to the epitaxial structure will have an impact on the reliability of LED,different package structure will also cause differences in reliability.Therefore,the aging experiment was carried out on the samples of three different yellow LED packaging structures.It was found that the initial aging operating voltage decreased significantly.The main reason is that in the process of aging,the ohmic contact between the metal-semiconductor becomes better under the common action of temperature and current.This made the resistance of the device decrease and the operating voltage becomes small.As the early operating voltage becomes smaller,the input power decreases.The attenuation of early optical power is mainly caused by the decrease of input power.Secondly,the different encapsulation mode has obvious influence on the attenuation of optical power,and the light failure of yellow-ray dispensing package mainly comes from the deterioration of the chip itself.For polycarbonate lens packaging,because of the difference of expansion coefficient between silica gel and polycarbonate lens,the interface between silica gel and polycarbonate lens changed,which affects the light output.For polycarbonate lens package,the silver mirror on the bracket is directly in contact with the air.In the high temperature environment,the silver mirror was oxidized and blackening,which affected the light output and has lagest light output power decay.