Effect Of Preparing Layer Structure On Performance Of InGaN-based LED On Silicon Substrtate

Thanks to the rapid improvements in epitaxial and novel structuring techniques,InGaN-based LEDs grown on silicon substrate employ InGaN/GaN multi quantum wells(MQWs)as active region,covering a wide spectral region from near ultraviolet to near infrared,making them attractive in solid-state lighting.Compared with blue LEDs,for LEDs emitting at green spectral region,InGaN/GaN MQWs with higher indium(In)composition are required.At present,growing InGaN quantum wells with high quality and high In composition is still challenging,resulting in the luminous efficiency of green LEDs being significantly lower than that of blue LEDs.And their typical external quantum efficiency(EQE)rises with increasing current and then appears a reduction after reaching a maximum.This phenomenon has been called as the efficiency droop effect of LED,and several mechanisms have been proposed as explanations,such as Auger recombination,carrier leakage.In order to further explore the luminescence mechanism and obtain silicon-based InGaN LEDs with better overall performance,this paper analyzes LEDs with different preparation layer structures.The effects of preparing layer design on the photoelectric performance and reliability of InGaN-based green LED grown on silicon substrate were studied.The main achievements are listed as follows:1.Combined with experimental and numerical simulation methods,the effect of n-AlGaN hole blocking layer(HBL)on the photoelectric performance of V-pits-containing InGaN-based green LEDs grown on silicon substrates was studied.And for the first time,we have direct observed hole overflow from MQWs and enter into InGaN/GaN superlattices(SLs)preparation layer recombine with electrons at room temperature.Experimental results show that sample with n-AlGaN HBL shows higher EQE and smaller efficiency droop at high current density range,even though it exhibits severe hole leakage.Numerical simulation suggests that the HBL can change the carrier flow path and allow more electrons to be injected into the MQWs through c-plane region,which could reduce nonradiative recombination near the sidewalls of V-pit.This will increase the carrier concentration in the MQWs,and eventually lead to higher EQE.Meanwhile,less electrons transported through V-pit allowed more holes injecting into deeper layers via V-pit sidewalls,and electroluminescence emission from the SLs layer became stronger when HBL was inserted.These results provide new understanding on the carrier transportation and recombination mechanisms in V-pits-containing InGaN-based LEDs.2.The effects of Si-doped InGaN/GaN blue-light multiple quantum wells(BMQWs)and traditional InGaN/GaN SLs preparing layers on the performance photoelectric and electro-static discharge(ESD)were studied.Compared to SLs,it is found that using BMQWs as part of preparing layer can increase the working voltage.Furthermore,when the position of Si-doped in BMQWs is adjusted from the middle of the quantum barrier to the well/barrier interface,the conduction band close to the quantum well bends downward,weakening the electron blocking barrier and reducing the working voltage of LED device.At the same time,the doping of Si in the preparing layer will increase the number of electrons injected into the active region,enhance the blocking of holes,and make it difficult for holes to leak into the preparing layer.In addition,using BMQWs as the preparing layer will also reduce the density of small V-pits in the active region,thereby improving the ESD performance of the device.3.The agig mechanism of blue and green LEDs using BMQWs as the preparing layer with the same epitaxial structure was studied.The aging results show that the EQE attenuation of blue LED sample was significantly greater than that of green LED sample after aging.XRD reciprocal space mapping results show that the stress in the quantum well of blue LEDs relaxes after aging.It is speculated that the possible reason for EQE attenuation significantly of blue LEDs with the same epitaxial structure after aging is that the aging process causes stress relaxation in the quantum well,forming new defects,resulting in increased nonradiative recombination.This work has reference value and guidance significance for revealing the aging mechanism of LED devices grown on silicon substrate.