In源流量与Ⅲ族流量之比对InGaN/GaN多量子阱性质的影响

利用x射线三轴晶衍射和光致发光谱研究了生长参数In源流量与Ⅲ族流量之比对InGaN/GaN多量子阱结构缺陷(如位错密度和界面粗糙度)和光致发光的影响.通过对（0002）对称和（1012）非对称联动扫描的每一个卫星峰的ω扫描，分别测量出了多量子阱的螺位错和刃位错平均密度，而界面粗糙度则由（0002）对称衍射的卫星峰半高全宽随级数的变化得出.试验发现多量子阱中的位错密度特别是刃位错密度和界面粗糙度随In源流量与Ⅲ族源流量比值的增加而增加，导致室温下光致发光性质的降低，从而也证明了刃位错在InGaN/GaN 关键词： x射线三轴晶衍射 界面粗糙度 位错 InGaN/GaN多量子阱     

Evaluation of polarization field in InGaN/GaN multiple quantum well structures by using electroluminescence spectra shift

In order to investigate the inherent polarization intensity in InGaN/GaN multiple quantum well(MQW) structures,the electroluminescence(EL) spectra of three samples with different GaN barrier thicknesses of 21.3 nm, 11.4 nm, and 6.5 nm are experimentally studied. All of the EL spectra present a similar blue-shift under the low-level current injection,and then turns to a red-shift tendency when the current increases to a specific value, which is defined as the turning point.The value of this turning point differs from one another for the three InGaN/GaN MQW samples. Sample A, which has the GaN barrier thickness of 21.3 nm, shows the highest current injection level at the turning point as well as the largest value of blue-shift. It indicates that sample A has the maximum intensity of the polarization field. The red-shift of the EL spectra results from the vertical electron leakage in InGaN/GaN MQWs and the corresponding self-heating effect under the high-level current injection. As a result, it is an effective approach to evaluate the polarization field in the InGaN/GaN MQW structures by using the injection current level at the turning point and the blue-shift of the EL spectra profiles.     

具有超晶格应力调制结构的绿光InGaN/GaN多量子阱的发光特性

研究了具有InGaN/GaN超晶格(SL)插入结构的绿光InGaN/GaN多量子阱(MQW)的发光特性。结构测试表明,SL插入结构并没有引起MQW中平均In组份的增加,而是改变了In组份的分布,形成了高In组份的量子点和低In组份量子阱。其电致发光(EL)谱和光致发光(PL)谱均出现了双发光峰。我们认为这两个 峰分别来自于量子点和量子阱,且存在着载流子从阱向点转移的输运机制。最后变温PL积分强度的Arrhenius 拟合表明,SL插入结构并没有在MQW中引入新的缺陷,使其发光效率下降。     

Effects of multiple interruptions with trimethylindium-treatment in the InGaN/GaN quantum well on green light emitting diodes

In this study, the influence of multiple interruptions with trimethylindium(TMIn)-treatment in InGaN/GaN multiple quantum wells(MQWs) on green light-emitting diode(LED) is investigated. A comparison of conventional LEDs with the one fabricated with our method shows that the latter has better optical properties. Photoluminescence(PL) full-width at half maximum(FWHM) is reduced, light output power is much higher and the blue shift of electroluminescence(EL) dominant wavelength becomes smaller with current increasing. These improvements should be attributed to the reduced interface roughness of MQW and more uniformity of indium distribution in MQWs by the interruptions with TMIn-treatment.     

GaN基激光器多量子阱垒材料的研究

在(0001)蓝宝石衬底上分别用金属有机化学气相沉积技术外延生长了InGaN/GaN, InGaN/InGaN, InGaN/AlInGaN多量子阱激光器结构, 并分别制作了脊形波导GaN基激光器。同步辐射X射线衍射,电注入受激发射光谱测试及光功率-电流(L-I)测试证明,相对于GaN垒材料,InGaN垒材料,AlInGaN四元合金垒材料更能改善多量子阱的晶体质量,提高量子阱的量子效率及降低激光器阈值电流。相关的机制为：组分调节合适的四元合金垒层中Al的掺入使得量子阱势垒高度增加,阱区收集载流子的能力增强;In的掺入能更多地补偿应力,减少了由于缺陷和位错所产生的非辐射复合中心密度;In的掺入还减小了量子阱中应力引致的压电场,电子空穴波函数空间交叠得以加强,使得辐射复合增加。     

InGaN/GaN超晶格厚度对Si衬底GaN基蓝光发光二极管光电性能的影响

采用有机金属化学气相沉积技术在Si(111)衬底上生长蓝光多量子阱发光二极管(LED) 结构, 通过在量子阱下方分别插入两组不同厚度的InGaN/GaN超晶格, 比较了超晶格厚度对LED光电性能的影响. 结果显示: 随超晶格厚度增加, 样品的反向漏电流加剧; 300 K下电致发光仪测得随着电流增加, LED发光光谱峰值的蓝移量随超晶格厚度增加而减少, 但不同超晶格厚度的两个样品在300 K下的电致发光强度几乎无差异. 结合高分辨X射线衍射仪、扫描电子显微镜、透射电子显微镜对样品的位错密度和V形坑特征分析, 明确了两样品反向漏电流产生巨大差异的原因是由于超晶格厚度大的样品具有更大的V形坑和V形坑密度, 而V形坑可作为载流子的优先通道, 使超晶格更厚的样品反向漏电流加剧. 通过对样品非对称(105)面附近的X射线衍射倒易空间图分析, 算得超晶格厚度大的样品其InGaN量子阱在GaN上的弛豫度也大, 即超晶格厚度增加有利于减小InGaN量子阱所受的应力. 综合以上影响LED发光效率的消长因素, 导致两样品最终的发光强度相近.     

High-efficiency InGaN/AlInGaN multiple quantum wells with lattice-matched AlInGaN superlattices barrier

A new approach to fabricating high-quality AlInGaN film as a lattice-matched barrier layer in multiple quantum wells(MQWs) is presented. The high-quality AlInGaN film is realized by growing the AlGaN/InGaN short period superlattices through metalorganic chemical vapor deposition, and then being used as a barrier in the MQWs. The crystalline quality of the MQWs with the lattice-matched AlInGaN barrier and that of the conventional InGaN/GaN MQWs are characterized by x-ray diffraction and scanning electron microscopy. The photoluminescence(PL) properties of the InGaN/AlInGa N MQWs are investigated by varying the excitation power density and temperature through comparing with those of the InGaN/GaN MQWs. The integral PL intensity of InGaN/AlInGaN MQWs is over 3 times higher than that of InGaN/GaN MQWs at room temperature under the highest excitation power. Temperature-dependent PL further demonstrates that the internal quantum efficiency of InGaN/AlInGaN MQWs(76.1%) is much higher than that of InGaN/GaN MQWs(21%).The improved luminescence performance of InGaN/AlInGaN MQWs can be attributed to the distinct reduction of the barrier-well lattice mismatch and the strain-induced non-radiative recombination centers.     

Effects of a prestrained InGaN interlayer on the emission properties of InGaN/GaN multiple quantum wells in a laser diode structure

The electroluminescence (EL) and photoluminescence (PL) spectra of InGaN/GaN multiple quantum wells (MQWs) with a prestrained InGaN interlayer in a laser diode structure are investigated. When the injection current increases from 5 mA to 50 mA, the blueshift of the EL emission peak is 1 meV for the prestrained sample and 23 meV for a control sample with the conventional structure. Also, the internal quantum efficiency and the EL intensity at the injection current of 20 mA are increased by 71% and 65% respectively by inserting the prestrained InGaN interlayer. The reduced blueshift and the enhanced emission are attributed mainly to the reduced quantum-confined Stark effect (QCSE) in the prestrained sample. Such attributions are supported by the theoretical simulation results, which reveal the smaller piezoelectric field and the enhanced overlap of electron and hole wave functions in the prestrained sample. Therefore, the prestrained InGaN interlayer contributes to strain relaxation in the MQW layer and enhancement of light emission due to the reduction of QCSE.     

In组分渐变提高InGaN/GaN多量子阱发光二极管发光性能

利用金属有机物化学气相沉积系统在蓝宝石衬底上通过有源层的变温生长,得到In组分渐变的量子阱结构,从而获得具有三角形能带结构的InGaN/GaN多量子阱发光二极管(LED)(简称三角形量子阱结构LED).变温光致发光谱结果表明,相对于传统具有方形能带结构的量子阱LED(简称方形量子阱结构LED),三角形量子阱结构有效提高了量子阱中电子和空穴波函数的空间交叠,从而增加了LED的内量子效率;电致发光谱结果表明,三角形量子阱结构LED器件与传统结构LED器件相比,明显改善了发光峰值波长随着电流的蓝移现象.通过以上     

具有三角形InGaN/GaN多量子阱的高内量子效率的蓝光LED(英文)

对InGaN量子阱LED的内量子效率进行了优化研究。分别对发光光谱、量子阱中的载流子浓度、能带分布、静电场和内量子效应进行了理论分析。对具有不同量子阱数量的InGaN/GaN LED进行了理论数值比对研究。研究结果表明,对于传统结构的LED而言,2个量子阱的结构相对于5个和7个量子阱具有更好的光学性能。同时还研究了具有三角形量子阱结构的LED,研究结果显示,三角形多量子阱结构具有较高的电致发光强度、更高的内量子效率和更好的发光效率,所有的优点都归因于较高的电子-空穴波函数重叠率和低的Stark效应所产生的较高的载流子输入效率和复合发光效率。     

Performance improvement of InGaN/GaN multiple quantum well visible-light photodiodes by optimizing TEGa flow

The performance of an InGaN/GaN multiple quantum well(MQW) based visible-light Schottky photodiode(PD)is improved by optimizing the source flow of TEGa during In Ga N QW growth. The samples with five-pair InGaN/GaN MQWs are grown on sapphire substrates by metal organic chemical vapor deposition. From the fabricated Schottky-barrier PDs, it is found that the smaller the TEGa flow, the lower the reverse-bias leakage is. The photocurrent can also be enhanced by depositing the In GaN QWs with using lower TEGa flow. A high responsivity of 1.94 A/W is obtained at 470 nm and -3-V bias in the PD grown with optimized TEGa flow. Analysis results show that the lower TEGa flow used for depositing In Ga N may lead to superior crystalline quality with improved InGaN/GaN interface, and less structural defects related non-radiative recombination centers formed in the MQWs.     

Luminescent Characteristics of Near Ultraviolet InGaN/GaN MQWs Grown on Grooved Sapphire Substrates Fabricated by Wet Chemical Etching

InGaN/GaN multiple quantum wells （MQWs） are grown on planar and maskless periodically grooved sapphires by metal organic vapour phase epitaxy （MOCVD）. High-resolution x-ray rocking curves and transmission electron microscopy （TEM） are adopted to characterize the film quality. Compared with the MQWs grown on planar sapphire, the sample grown on grooved sapphire shows better crystalline quality： a remarkable reduction of dislocation densities is achieved. Meanwhile, the MQWs grown on grooved sapphire show two times larger PL intensity at room temperature. Temperature-dependent PL measurements are adopted to investigate the luminescence properties. The luminescence thermal quenching based on a fit to the Arrhenius plot of the normalized integrated PL intensity over the measured temperature range suggests that the nonradiative recombination centres （NRCs） are greatly reduced for the sample grown on grooved sapphire. We assume that the reduction of dislocations which act as NRCs is the main reason for the sample grown on pattern sapphire having higher PL intensity.     

Influence of growth parameters on the properties of InGaN/GaN multiple quantum well grown by metalorganic chemical vapor deposition

The effects of growth parameters such as barrier growth time, growth pressure and indium flow rate on the properties of InGaN/GaN multiple quantum wells (MQWs) were investigated by using photoluminescence (PL), high resolution X-ray diffraction (HRXRD), and atomic force microscope (AFM). The InGaN/GaN MQW structures were grown on c-plane sapphire substrate by using metalorganic chemical vapor deposition. With increasing barrier growth time, the PL peak energy is blue-shifted by 18 nm. For InGaN/GaN MQW structures grown at different growth pressures, the PL intensity is maximized in the 300 Torr – grown structure, which could be attributed to the improved structural quality confirmed by HRXRD and AFM results. Also, the optical properties of InGaN/GaN MQW are strongly affected by the indium flow rate.     

Photoluminescence study of InGaN/GaN multiple-quantum-well with Si-doped InGaN electron-emitting Layer

InGaN/GaN multiple-quantum-well (MQW) structure with Si-doped InGaN electron-emitting layer (EEL) was grown by metal–organic chemical vapor deposition and their characteristics were evaluated by photoluminescence (PL) measurements. In a typical structure, a low indium composition and wide potential well was used to be an EEL, and a six-fold MQW was used to be an active layer where the injected carriers recombine. By comparing the PL spectral characteristics of the MQW samples, the PL intensity of MQW with EEL is about 10 times higher than that of typical MQW. Experimental results indicate that the high electron capture rate of the MQW active region can be achieved by employing EEL.     

垒层厚度对InGaN/GaN多量子阱电注入发光性能的影响及机理

研究了不同垒厚对InGaN/GaN多量子阱电注入发光性能的影响及机理。实验发现,当GaN垒层的厚度从6 nm增大到24 nm时,垒厚的样品发光强度更强,而且当注入电流增加时,适当增加垒厚,可以更显著增加发光强度。进一步结合发光峰位和光谱宽度的研究表明,由于应力和极化效应的存在,当垒层厚度在6~24 nm范围内时,适当增加垒层厚度不仅会使得能带的倾斜加剧,减少电子泄露,而且也会增加InGaN阱层的局域态深度,从而改善量子阱的发光性能。     

Strain Effect on Photoluminescences from InGaN MQWs with Different Barriers Grown by MOCVD

InGaN/GaN MQWs, InGaN/AlGaN MQWs and InGaN/AlInGaN MQWs are grown on （0001） sapphire substrates by MOCVD. Membrane samples are fabricated by laser lift-off technology. The photoluminescence spec-ra of membranes show a blue shift of peak positions in InGaN/GaN MQWs, a red shift of peak positions in InGaN/AlGaN MQWs and no shift of peak positions in InGaN/AIlnGaN MQWs from those of samples with substrates. Different changes in Raman scattering spectra and HR-XRD （0002） profile of InGaN/AlInGaN MQWs, from those of InGaN/GaN MQWs and InGaN/AlGaN MQWs, are observed. The fact that the strain changes differently among InGaN MQWs with different barriers is confirmed. The AIlnGaN barrier could adjust the residual stress for the least strain-induced electric field in InGaN/AIlnGaN quantum wells.     

Influence of barrier thickness on the structural and optical properties of InGaN/GaN multiple quantum wells

The structural and optical properties of InGaN/GaN multiple quantum wells(MQWs) with different barrier thicknesses are studied by means of high resolution X-ray diffraction(HRXRD), a cross-sectional transmission electron microscope(TEM), and temperature-dependent photoluminescence(PL) measurements. HRXRD and cross-sectional TEM measurements show that the interfaces between wells and barriers are abrupt and the entire MQW region has good periodicity for all three samples. As the barrier thickness is increased, the temperature of the turning point from blueshift to redshift of the S-shaped temperature-dependent PL peak energy increases monotonously, which indicates that the localization potentials due to In-rich clusters is deeper. From the Arrhenius plot of the normalized integrated PL intensity, it is found that there are two kinds of nonradiative recombination processes accounting for the thermal quenching of photoluminescence,and the corresponding activation energy(or the localization potential) increases with the increase of the barrier thickness.The dependence on barrier thickness is attributed to the redistribution of In-rich clusters during the growth of barrier layers,i.e., clusters with lower In contents aggregate into clusters with higher In contents.     

Modeling and analysis of the effects of inhomogeneous carrier distributions in InGaN multiple quantum wells

It is well known that carrier distribution in InGaN multiple quantum wells (MQWs) can be significantly inhomogeneous. However, the conventional ABC recombination model assumes that carriers are uniformly distributed throughout the MQW. In this paper, a modified ABC model that considers the unequal carrier density in the QWs was developed. From the analysis of the developed ABC model, the effective recombination coefficients and modified internal quantum efficiency (IQE) were obtained for an arbitrary carrier distribution in MQWs. The efficiency droop was found to be aggravated as the carrier distribution was increasingly inhomogeneous. However, it was also found that the effect of inhomogeneous carrier distribution alone was not sufficient to explain the IQE droop with the theoretical Auger recombination coefficient based on indirect Auger processes. The developed ABC model is expected to provide insight into the influence of inhomogeneous carrier distributions in MQWs on the efficiency droop in GaN-based light-emitting diodes.     

局域表面等离激元对InGaN/GaN多量子阱发光效率的影响

Ag纳米粒子的形貌对InGaN/Ga N多量子阱(MQWs)的光致发光(PL)效率有着显著影响。本文采用离子束沉积(IBD)技术将Ag沉积在InGaN/Ga N MQWs上,然后通过快速热退火处理制备Ag纳米粒子。通过改变Ag的沉积时间获得了具有不同Ag纳米粒子形貌的样品。用原子力显微镜对各样品的Ag纳米粒子形貌和尺寸进行了表征,并且测试了吸收谱、室温和变温PL谱及时间分辨光致发光(TRPL)谱。结果表明:随着Ag沉积时间的延长,所得Ag纳米粒子粒径增大,粒子纵横比先增大后减小且吸收谱峰红移。由于不同形貌的Ag纳米粒子在入射光作用下产生的局域表面等离激元(LSPs)与MQWs中激子耦合强度不同,光发射能力也不同,与没有Ag纳米粒子的样品相比,沉积时间为15 s的样品室温PL积分强度被抑制6.74倍,沉积时间为25 s和35 s的样品室温PL积分强度分别增强1.55和1.72倍且峰位发生红移,沉积时间为45 s的样品室温PL积分强度基本没有变化。TRPL与变温PL的测试结果证明,室温PL积分强度的改变是由于LSPs与MQWs中的激子耦合作用引起的。纵横比大且吸收谱与MQWs的PL谱交叠大的Ag纳米粒子能够更好地增强InGaN/Ga N MQWs的发光。     

Effects of strain-compensated AlGaN/InGaN superlattice barriers on the optical properties of InGaN light-emitting diodes

In this article, metalorganic chemical vapor deposition (MOCVD)-grown InGaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with Al_0.03Ga_0.97N and Al_0.03Ga_0.97N/In_0.01Ga_0.99N superlattices-barrier layers on c-plane sapphire were studied for the influence of the strain-compensated barrier on the optical properties of the LEDs. High-resolution X-ray diffraction (HRXRD) analysis shows that the LEDs with a strain-compensated superlattice barrier (SC-SLB) have better interface quality than those using AlGaN. This difference in quality may result from the alleviation of strain relaxation in superlattice layers to improve the crystalline perfection of the epitaxial structures. It was also found that the degree of the exciton localization effect rises considerably as InGaN grows directly on the AlGaN barrier layers. However, the increase in the strength of the polarization fields within the MQWs (as evaluated from bias-dependent photoluminescence (PL) measurement) could reduce the radiative efficiency of the LEDs and shift their PL peaks toward long wavelengths. With suitable control of crystalline quality and the reduced quantum-confined Stark effect in the MQWs, the SC-SLB LEDs operating at 150-mA-current show a 22.3% increase in light output power as compared to their conventional counterparts.