Study On The Optical Properties Of InGaN/AlGaInN Quantum Wells

Group ? nitride semiconductor has great physical and chemical properties,making it a promising material for optoelectronic devices.In 1990s,the realization of high brightness GaN based blue LEDs promoted the research on Group III nitride based LEDs,the solid state lighting technology on the basis of it have been developed immediately as well.Comparing with conventional lightings,LEDs have many advantages like high brightness,long lifetime,energy-saving,environment-friendly and so on.The researches on the luminescence mechanism and performance enhancement of InGaN/GaN quantum wells,which is the core structure of LEDs,have been the research hotspot for many years.Quantum wells can effectively confine the carriers,being good for QWs luminescence.Besides,the bandgap can be continuously adjusted from 0.7eV to 3.4Ev by adjusting the In component.In the past decades,the researches on the InGaN/GaN quantum wells have made great progress,but there are still many problems need to be resolved.Based on the previous reports,the polarization effect in InGaN/GaN QWs which is induced by the lattice mismatch can seriously degrade the luminescence efficiency.In order to elevate the luminescence efficiency by weaken the strain,we designed a InGaN/AlGaInN QWs structure,taking place of GaN barrier layers by InGaN/AlGaN super lattices.Theoretically,the equivalent crystal constants of the InGaN/AlGaN super lattice can match that of InGaN well layers by adjusting the In and Al component.Regarding this,we took InGaN/GaN QWs and InGaN/AlGaInN QWs as samples.Then,we examined the surface morphology by SEM and obtained the luminescence properties by testing the PL spectra.By analyzing the surface morphology and the luminescence properties under different exciting power and temperature,we obtained the following conclusions,(1)The V-pits density of InGaN/GaN QWs is 2.79 × 107/cm2 and the V-pits density of InGaN/AlGaInN QWs is 8.43 × 105/cm2.Since the formation of V-pits is related to the strain,the phenomena shows the strain in InGaN/AlGaInN QWs has been effectively reduced by using the InGaN/AlGaN super lattice.(2)The peak wavelength of InGaN/GaN QWs has a blue shift about 10nm with the increasing exciting power,while the peak wavelength of InGaN/AlGaInN QWs have no obvious change with the increasing exciting power.Calculation result shows that the polarization electric filed strength in InGaN/GaN QWs is 2.04×105 V/cm2.Since the peak wavelength of InGaN/AlGaInN QWs is almost free from the increasing exciting power,it means that there is no obvious polarization effect in InGaN/AlGaInN QWs.(3)When the excitation power reaches 400mV/cm2,the integral intensity of the InGaN/AlGaInN MQWs is 3.6 times larger than that of InGaN/GaN MQWs.The result indicate that by reducing the strain in the MQWs can effectively enhance the light intensity of MQWs.(4)With the rose of the temperature,the FWHM of InGaN/GaN MQWs increase.It can be attributed to the thermal excitation of carriers and multi-level participation in radiation recombination.The FWHM of InGaN/AlGaInN MQWs only increase 2nm with the rose of temperature indicating that only thermal excitation effect the increase of the FWHM.This result show that the In composition in InGaN/AlGaInN MQWs is more even.(5)The integral intensity of InGaN/GaN MQWs decrease with the rose of temperature.It can be attributed to the activity of non-radiation recombination center.The decrease of integral intensity of InGaN/AlGaInN MQWs after 125K can also be attribute to the activity of non-radiation recombination center.In the range of 6K?125K,the integral intensity increases with increasing temperature,which can be explained by the low probability of exciton scattering at low temperature,long lifetime,low radiation probability,and therefore low integral intensity;the increase in temperature leads to enhanced lattice scattering,and exciton The probability of radiation increases so that the integral intensity of the quantum well luminescence gradually increases.By calculating the room temperature,the internal quantum efficiency of InGaN/GaN quantum wells is 19%,and the internal quantum efficiency of InGaN/AIGaInN quantum wells is 35%.The results show that the InGaN/AlGaInN quantum wells can improve the integral intensity of the quantum well luminescence by improving the weakening stress and improving the quality of the sample.