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Study Of Luminescence Properties On InGaN/GaN Multi-quantum Well Based LED

Posted on:2023-05-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:R LiFull Text:PDF
GTID:1528306614983689Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
As a new lighting sources,light-emitting diodes(LEDs)have attracted extensive attention and great interest of researchers due to the advantages of long life,low power consumption and friendly environment.According to their different implementations,white LEDs can be divided into three types:phosphor-converted white LEDs,multi-chip white LEDs,and monolithic white LEDs.The monolithic white LEDs can not only avoid the Stokes’loss in phosphor-converted white LEDs,but also avoid the lighting color drift in multi-chip white LEDs,which is the development direction of white LEDs lighting in the future.As the third generation semiconductor material,InGaN is an ideal candidate for the preparation of monolithic white LEDs,because of its wide adjustable band gap range(0.73-44 eV)and the corresponding wavelength covering the whole visible light range(theoretically,white light can be obtained by designing the active region of the LED epitaxial structure as InGaN multilayer stacks that emits blue,green,and red light,respectively).Currently,InGaN/GaN multiple quantum well(MQW)-based LEDs with short wavelengths(such as blue)have been found to have a high external quantum efficiency(EQE)of about 80%and has been realized for commercial application.However,with increasing the In component(i.e.,the emission wavelength gradually increases),the EQE of InGaN/GaN MQW-based LEDs decreases significantly,and this has become one of the biggest constraints to the realization of monolithic white LEDs.Therefore,in order to realize the preparation of InGaN/GaN MQW-based LEDs with high efficiency and long wavelength,and facilitate their commercial application,based on the relatively mature preparation techniques(including growth techniques and structural parameters)of InGaN/GaN MQW-based LEDs with short wavelength(blue),we continuously optimize or improve these techniques and parameters to gradually increase their emission wavelength and improve their emission efficiency.Such as,the effects of well layer growth rate(Rwell)and well layer growth temperature(Twell)on the emission characteristics of blue-emitting InGaN/GaN MQW samples are studied,and the experiences in improving their emission properties are obtained,which provide experimental and theoretical references for improving the emission efficiency of InGaN/GaN MQW sample with long wavelength in the next step;InGaN/GaN MQW samples with long wavelength(green)were prepared by appropriately reducing the growth temperature of well and barrier layers to increase the In component,and the effect of Twell on their emission characteristics was analyzed,which provides references for the preparation of InGaN/GaN MQW sample with longer wavelength;based on the comprehensive analysis of the relevant research results of blue and green-emitting samples,InGaN/GaN trapezoidal MQW(TMQW)samples with longer wavelength(red)were prepared by using energy band engineering and stress regulation(such as introducing low-temperature interlayers(ITILs)into the active region)and further reducing the growth temperature of well and barrier layers,and the effect of ITILs on its luminescence properties was studied.The main research contents of the dissertation are as follows:1.Effect of Rwell on luminescence characteristics of InGaN-based blue-emitting samplesSeveral blue-emitting samples with different Rwell were prepared,and the temperature-dependence of their luminescence spectra indicated that,within the Rwell range in this work,the InGaN well layers of all samples are composed of two separate phases(In-rich clusters and an InGaN matrix),also,with increasing Rwell,the density of states of the In-rich clusters should increase significantly relative to that of the InGaN matrix,the depths of the localized states in their respective phases become more homogeneous and the internal quantum efficiency(IQE)increases.These characteristics are interpreted thus:an increasing Rwell can shorten exposure of the upper layer face to the atmosphere during the growth of InGaN well layers,and this suppresses the migration of In atoms on the surface from the In-rich clusters to the surrounding InGaN matrix,thus suppressing the dissociation of In-rich clusters,the composition fluctuations in their respective phases,and the production of non-radiative centers.2.Effect of Twell on luminescence characteristics of InGaN-based blue-emitting samplesSeveral blue-emitting samples with different Twell were prepared,and the temperature-dependence of their luminescence spectra indicated that,within the scope of this work,a decreasing Twell can result in a conversion of the well layer structure from a one-zone structure into a two-zone(zone-Ⅰ and zone-Ⅱ)structure,due to the increased In content-induced enhanced component fluctuation.In addition,we also found that,ⅰ)the two-zone structure of low Twell sample leads to an unusual "M-shaped" temperature-dependent behavior of EQE at the intermediate fixed currents,this behavior is considered to be related to the transfer of localized carriers between two zones,since this transfer leads to a marked loss in optical energy due to interfacial misfit defect-related non-radiative decay;ⅱ)compared with the high Twell sample,the low Twell sample exhibits higher EQEs at 300 K,which was attributed to its stronger zone-Ⅱ-related localization effect.3.Effect of Twell on luminescence characteristics of InGaN-based green-emitting samplesSeveral green-emitting samples with different Twell were prepared,and the excitation power-dependence of their luminescence spectra indicated that,the emission processes of all the samples in this work are dominated simultaneously by the carrier scattering effect and Coulomb screening effect,but both the scattering effect and the screening effect in the process are stronger for low Twell sample than for high Twell sample.These characteristics can be ascribed to the fact that,compared with the high Twell sample,the low Twell sample has a higher In content in the MQWs,and this results in the more significant compositional fluctuation-induced potential fluctuation and the stronger well/barrier lattice mismatch-induced QCSE.In addition,we also found that,within the scope of this work,with increasing Twell,the IQE increases in the initial excitation power range and decreases in the high excitation power range.The former is due to the stronger carrier localization effect,and the latter is mainly because of the presence of more numerous defect-related non-radiative centers.4.Effect of LTILs in active-region on luminescence characteristics of InGaN-based red-emitting samplesTwo red-emitting samples with different LTILs(GaN and AlN)were prepared,and the excitation power and temperature-dependence of their luminescence spectra indicated that,for the AlN LTILs sample,the InGaN well layers are composed of two separate phases(In-rich QDs and InGaN matrix);in contrast,for the GaN LTILs sample,the InGaN well layers demonstrate a significant and disordered component fluctuation.Meanwhile,compared with the latter,the former also have a better structural quality,more significant carrier localization effect,and superior IQE.This can be explained by the fact that due to the stability of Al-N bond and strain compensated effect of AlN,compared with the GaN LTILs,the AlN LTILs grown on the InGaN well layer with embedded In-rich QDs,cannot only reduce threading dislocation densities,but also prevent the diffusion of In atoms from In-rich QDs into the InGaN matrix and/or from the InGaN well into the GaN barrier layer,thus suppressing degradation of QDs,the weakening of localization effect,and production of non-radiative centers.
Keywords/Search Tags:InGaN/GaN multiple quantum wells, Light emitting diode, Carrier localization effect, Photoluminescence, Electroluminescence, Low-temperature interlayer
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