Study On Electrical Stress Aging Of GaN-based Green LED On Silicon Substrate

GaN-based LEDs are widely used in high-quality display,lighting and other fields because of its advantages of high brightness,long life,energy conservation,environmental protection,moisture resistance,shock resistance and so on.It has made an important contribution to global energy conservation and environmental protection.At present,multi-primary colors mixed LEDs lighting technology is considered to be the mainstream of high-quality full-spectrum LED lighting in the future due to its advantages such as low color temperature,high color rendering index,and high efficiency.However,the key to realizing multi-primary colors mixed LED lighting is to improve the luminous efficiency of LEDs in the yellow-green light band.In addition,the reliability problems reflected in the applications of GaN-based LEDs are becoming increasingly prominent.As an important part of the multi-primary colors mixed LED lighting technology,it is particularly important to improve the luminous efficiency and reliability of GaN-based green LEDs to realize the wide application of high-quality multi-primary colors mixed LEDs lighting.Since the quantum well as active region and its pre-well preparation layer have a crucial impact on the photoelectric performance of LED,this dissertation studies the effect of quantum well and preparation layer on the photoelectric properties of GaN-based green LEDs on silicon substrate under electrical stress aging.The main conclusions are as follows:1.The effect of AlGaN interlayer on the luminous efficiency and reliability of green LEDs was investigated by inserting AlGaN interlayers of a certain thickness into the four quantum barriers near the n-layer and the final barrier near the p-layer in the InGaN/GaN multi-quantum well of green LED.The results show that the AlGaN interlayers in the quantum barriers can effectively improve the role of V-pits in screening dislocations and regulate the carrier distribution,thereby greatly improving the luminous efficiency of LED devices and reducing the forward leakage current.However,the insertion of AlGaN interlayers could more easily induce the generation or proliferation of defects in the active region of the device during electrical stress aging,which leads to a large light decay of the LED devices at low current density.2.The effect of the number of quantum wells on the photoelectric properties of GaN-based green LEDs on silicon substrates before and after electrical stress aging was studied.The results show that with the increase of the number of quantum wells,the distribution of In component in the quantum wells is more uniform,and the phase separation of In is weakened.However,when the number of quantum wells is increased to 9,it will adversely affect the well/barrier interface and crystal quality of the quantum wells,resulting in lower external quantum efficiency(EQE)of the device at low current density.As the number of quantum wells increases,the effective active region volume of radiation recombination increases,and more carriers are restricted to participate in the emission in the active region,so that the carrier leakage decreases,and the average carrier concentration in the quantum well is relatively small,Thereby improving the efficiency of the device at high current density and the reliability of the device.In this paper,the optimal number of quantum wells for the green LED structure is 9.3.The thickness of the preparation layer was changed by changing the growth rate of the preparation layer,and the effect of the thickness of the preparation layer on the photoelectric properties of the GaN-based green LEDs before and after electrical stress aging was studied.The results show that the thicker the preparation layer of the sample,the worse the crystal quality of the quantum wells,so it shows lower luminous efficiency at low current density.Nevertheless,increasing the thickness of the preparation layer also increases the size and density of the V-pits in the active region,which can shield dislocations and inhibit non-radiative recombination,thus improving the efficiency of device at high current density and the reliability of the device.