Study On The Effect Of Structure And Technology Of P-type Layer On The Performance Of GaN Based Long Wavelength LED On Si Substrate

Since the birth of the GaN based LED technology,the optimal growth of p-layer is one of the main issues to further improve the optoelectronic performance of LEDs.Among them,as an epitaxial growth technology that can effectively improve the optoelectronic performance of GaN-based LEDs on Si substrate,the V-pit technology has received extensive research and attention.During epitaxial growth,unintentionally doped GaN which grown at high temperature and pressure was adopted to cover the grown V-pits.The V-pit covering layer,as an important part of the V-pit technology,has an important influence on the optoelectronic performance of GaN-based LEDs on Si substrate.Therefore,in order to further improve the optoelectronic performance of GaN-based long wavelength LEDs on Si substrate,on the platform of the National Institute of LED on Silicon Substrate,this paper has carried out systematic research work around the optimization of the structure and growth temperature of p type layer.The effect of V-pit covering layer position,the growth temperature of p type layer and the thickness of p-AlGaN electronic barrier layer on the microstructure and optoelectronic performance of GaN based long wavelength LEDs on silicon substrate were studied.The main obtained results are as follows:1.the effect of VCL position on the optoelectronic performance of GaN-based long wavelength LED on Si substrate was studied.The results show that the VCL position has little effect on the optoelectronic performance at room temperature.When V-pits covered earlier,the reverse leakage current is smaller.The position of VCL could greater effect the carrier injection behavior near the V-pits at cryogenic temperature.When V-pits covered earlier,the holes near the V-pits are mainly injected from the platform,resulting in a sharp increase in voltage,the external quantum efficiency is higher at lower current,and lower at hight current.However the increase of voltage could lead to the opeaning of more V-pits sidewall quantum wells,and then some holes could be injected into quantum wells near the n-type layer via the sidewall of V-pits.When V-shaped pits covering later,the holes near the V-pits are mainly injected from the V-pits sidewall,so the voltage is lower,and the opeaning number of quantum wells on the V-pits sidewall is small.As a result,the holes are mainly injected from the V-pits sidewall into the quantum walls near the p-type layer.2.The effect of p type layer growth temperature on the microstructure and optoelectronic performance of GaN-based green LED on Si substrate is studied.The results show that properly reducing the growth temperature of p type layer can effectively suppression the formation of in rich clusters in quantum wells and improve the crystal quality of quantum wells.However,when the growth temperature ofp type layer is too low,such as 960?,it is not conducive to the covering of V-pits,resulting in V-shaped defects on the surface.With the increase ofp type layer growth temperature,the inerdiffusion of In atoms between quantum wells and quantum barriers could be enhanced,resulting in the increase of effective carrier recombination volume and the decrease of Auger recombination rate under the same current caused by the broadening of quantum well.But the excessive p type layer growth temperature will also lead to the increase of defects,result in the decrease of IQE under high current density.3.The effect of p-AlGaN EBL thickness on the optoelectronic performance and carrier transport of GaN based yellow LED on Si substrate was studied.The results show that properly increasing EBL thickness could enhance the effect of V-pits screen the defects,improve the efficiency of holes injected from the V-pits sidewalls into the quantum wells,and then increase the radiation recombination rate and the IQE at room temperature.However,the over thickness of EBL could result in the hole concentration in quantum wells decreased,and then the radiation recombination rate and the IQE redused.At cryogenic temperature,with the increase of p-AlGaN EBL thickness,the holes can be injected into the quantum wells which closer to n-GaN,and even the superlattice layer via the sidewall of V-pits.This is mainly due to the voltage rise of platform,which leads to the voltage of V-pits sidewall else rise,then the opeaning numbers of quantum wells on the V-pits sidewall increased and the holes could get more kinetic energy.The IQE droop increases gradually with the increase of EBL thickness at 100 K,which is mainly attribute to the decrease of effective hole concentration in quantum wells with the increase of EBL thickness.In conclusion,for the GaN-based LED on Si substrate with V-shaped pit structure,the change of p type layer structure and growth conditions have a great influence on the carrier injection near the V-shaped pit,the well/barrier interface quality,the formation of in rich clusters in the quantum well,and efficiency droop.Therefore,the subsequent research on the direction of p-layer optimization,on the one hand,could focus on how to improve the V-pits sidewall hole injection efficiency on the basis of ensuring or further improving the quality of p-layer crystal.On the other hand,could focus on the modify of the quantum well structure to further improve the efficiency of silicon-based GaN LED with the optimization ofp type layer growth temperature.