Study On Photoelectric Properties And Aging Reliability Of GaN-based Yellow LED On Silicon Substrate

With the improvement of science and technology,GaN-based LED is gradually entering people's life and becoming an indispensable part due to its advantages of good performance,high luminous efficiency,long service life,relatively small light decay,energy saving and environmental protection.Because phosphors have an adverse effect on the reliability of the LED device,not environmentally friendly and easy to pollute,so no fluorescent powder high quality white LED because of its high color rendering index,low color temperature,less blue,and pollution-free etc it gradually becomes the mainstream of the semiconductor lighting industry.But the biggest obstacle to this technology is the luminous efficiency of yellow leds.In 2019,Jiang Feng-Yi's team has successfully achieved the luminous efficiency of 26.7%of GaN-based yellow LED with Si substrate with a peak wavelength of 565 nm.As an important part of full-spectrum white LED,yellow LED cannot be commercially produced if its reliability fails to meet certain standards.However,due to the late development of yellow LED,the international reliability analysis of yellow LED is less.Therefore,this paper studies the photoelectric performance and reliability of GaN-based yellow LED.1.We studied the effect of growth temperature on InGaN/GaN superlattice preparation layer of GaN based yellow LED on Si substrate including photoelectric and aging properties.It was found that the external quantum efficiency of the sample with higher growth temperature of the preparation layer was higher than that of the samples with the lower growth temperature.After 1000 hours of aging at 500 mA,the light decay of the samples with higher growth temperature of the preparation layer is relatively larger.The electroluminescent spectra of 100 K before and after aging showed that the hole injection pathway of high-temperature-grown sample changed after aging,and the non-radiative composite center of high-temperature sample increased more after aging.Fluorescence microscope showed that a large number of dark spots appeared before aging,the color of high-temperature sample was darker,and the color of low temperature sample was lighter and red.The number of dark spots of high-temperature sample increased after aging,but the quantity of low temperature sample did change small,which may also be one of the reasons for the higher light decay of samples with high superlattice temperature.2.On the growth of yellow light LED cap layer GaN time adjustment,after studied the different trap cap layer thickness on the Si substrate GaN based yellow LED photoelectric properties and aging properties.At low current density,EQE of sample B with relatively thick cap layer is relatively small,while at high current density,EQE of sample B is larger than that of sample A.This is because under low current density,the cap layer of sample B is thicker,and the local state density is lower,and the probability of non-radiative recombination increases,so the luminescence efficiency is lower.Under high current density,samples with thick cap layer have steep barrier interface and better quantum well quality,which have stronger restriction on carrier and make the luminous efficiency higher.Under the same current density,the half-peak width of sample A with A relatively thin cap layer is wider than that of sample B with A relatively thick cap layer,possibly because the relative blurring of the quantum well interface of sample A makes the quantum well uneven in width.Aging after 1000 hours,the sample of the cap layer is relatively thick B its maximum droop,probably because the cap layer is relatively thick sample B,and under the small current density into chip carrier is captured at more easily in the defect,or through the tunnel current path,so that it has more flaws,SRH non radiative recombination is more serious,resulting in a decline in the efficiency of the larger.3.Accelerated aging experiments were carried out to study the aging mechanism of GaN based yellow light LED on Si substrate.The optical distribution instrument showed the chip current expansion of the two samples after aging,and it was found that the part of sample B with a large aging current far away from the chip electrode emitted less light.This may be caused by too much aging current,which causes congestion and burns to parts of the electrode,resulting in poor light distribution.In addition,after aging for 24 hours,EQE of the two groups of samples decreased significantly,and the aging temperature of sample A under the conventional aging mode was relatively high,so the defect was activated by heat,and the probability of SRH non-radiation recombination increased,and the radiation recombination decreased,so that the efficiency attenuation of sample A was more serious and EQE decreased more.The reverse leakage current of the three samples increased with the increase of the test temperature and the reverse voltage,but the reverse leakage current of sample B was the largest at room temperature.This is because the aging current of sample B is greater than that of sample A,and the potential barrier at the defect center is more prone to tilt,making the carrier easy to escape from the defect center and forming a greater leakage current.The chip quality near the middle position is better than that at the edge position,and the light attenuation is relatively small.This is because in epitaxial growth,at the edge of the platform,the stress of the material is alleviated,making it easier for In component to be incorporated,making the In component at the edge of the platform relatively high,making the barrier interface worse and the crystal mass worse.