The Effect Of V-pit On The Photoelectric Properties Of GaN Based Long Wavelength LED On Si Substrate

Full-spectrum LED illumination is the trend of future lighting market,however,the efficiency of yellow and green LEDs are too low to meet with the requirement of full-spectrum LED illumination,which restricts the development of full-spectrum LED illumination.So,how to elevate the luminous efficiency of long-wavelength LED needs to be resolved immediately.This paper starts with the V-shaped pits located in the MQW based on our previous research achievement,and then we make use of the experiment method and numerical simulation software to study the influence of V-shaped pits on the photoelectric properties of long-wavelength LED.The research results are shown as below:1.By adjusting the thickness of AlN buffer layer prior to n-GaN layer,we have got three kinds of different V-shaped pits density samples,the effect of V-shaped pits density located in the MQW on the external quantum efficiency(EQE)of Si substrate GaN based green LED was studied.The results show that we have got the different V-shaped pits density epitaxy materials which are 7.96×108,9.17×108,11.02×108cm-2,respectively,and the quality of the well/barrier interface has not been destroyed with the increasing pits density.At low current density,the larger pit density is good to the incorporation of In atoms,which attributes to the better crystal quality of quantum well,and the EQE of three samples are elevating with the increasing pits density,the maximum of EQE increases and the peak EQE value of corresponding current density(Jmax)shifts left.At high current density,the EQE of three samples are increasing and then falling with the increasing pits density.The increasing EQE attributes to the roles of V-shaped pits in improving the hole injection;And the falling EQE is due to the small area of emissive region caused by the excessive increase of pits area ratio,which aggravates the carrier leakage and auger recombination.At the current density of 20 A/cm2,the EQE of the three samples are 35.24%,36.45%,33.9%,respectively,indicating that there is a balanced area ratio of pits between V-shaped pits enhancing hole injection and enough emissive area.According to the experimental results,the probable optimal value of V-shaped pits area ratio in the green LED is about 23%at the current density of 20 A/cm2.2.With the help of numerical simulation software named Silvaco TCAD,the effects of HBL on the hole injection and internal quantum efficiency(IQE)in the yellow LED are explored.The results show that the IQE is reduced after employing the hole blocking layer in p region(HBLP).Based on the analyses of results,the V-pit hole current ratio elevates from 23.08%to 98.44%after we employ the n-GaN layer as the hole blocking layer in p region(GaN HBLP),however,this insert layer increases the electron leakage from flat region,and then the leaked electrons will take part in non-radiative recombination with holes in the p layer,causing the lower IQE.When we employ the n-Al0.5Ga0.5N as the HBLP(Al0.5Ga0.5N HBLP),Al0.5Ga0.5N HBLP can elevate the V-pit hole current ratio to 99.05%and reduce the electron leakage from the flat region,whereas it will force the electron leakage from the V-pit into p region,the electrons will take part in non-radiative recombination with holes and this will lead to the reduction of IQE.On the basis of HBLP,we employ the unintentionally doped AlN as the hole blocking layer in n region(AlN HBLN),this insert layer can not only alleviate the electron leakage from the V-pit into p region,but also reduce the hole leakage from the V-pit into the preparation layer,elevating the IQE and forward voltage.3.The optimized analysis of yellow LED structure are studied by the use of the yellow LED numerical models.It is found that the 100-nm-thick Al0.5Ga0.5N HBLP(Si-doped:1×1017 cm-3)could decrease the electron leakage from the flat region,slightly increasing the IQE.The AlN HBLN(unintentionally doped:5×1016 cm-3)is efficient to block the holes and electrons leak from the V-shaped pit.The density corresponding to the maximum IQE value is about 3×109 cm-2 in the yellow LED,which the V-shaped pits area ratio is about 55%.