AIGaN基紫外LED关键制备技术的研究

发布时间：2018-05-03 05:17

本文选题：Al_xGa_(1-x)N + 金属有机物化学气相沉积　；参考：《东南大学》2015年博士论文

【摘要】：AlxGa1-xN是直接带隙宽禁带半导体材料,化学性质稳定,耐高温,抗辐射,波长在200～365 nm范围内连续可调,在空气净化、杀菌与消毒、半导体固态照明等领域具有广泛的应用前景。AlGaN薄膜晶体质量对器件光电性能有很大影响,尤其制备紫外LED所需的高A1组份AlGaN材料的生长、量子阱结构的设计、极化效应的影响等一直是制约紫外LED发展的关键因素。因此,对AlGaN薄膜生长和表征的深入研究显得尤为重要。本论文采用金属有机物化学气相沉积(MOCVD)的方法制备了高质量的不同Al组分的AlGaN薄膜,并且系统地研究了AlGaN材料的物性,进而生长和表征了更具实用价值的AlInGaN四元材料的物性,同时从理论上研究了AlInGaN四元材料对于提高LED光电性能的影响。通过对生长工艺的优化,制备了高质量的AlGaN/GaN多量子阱,为制备AlGaN基紫外LED打下了坚实的基础。另外,对基于非极性与半极性蓝宝石衬底上的GaN与AlGaN外延生长进行了系统的实验探究。采用高分辨X射线衍射(HR-XRD)、扫描电子显微镜(SEM)、光致发光谱(PL)、X射线光电子能谱(XPS)、同步辐射X射线光谱等手段,对外延材料的晶体质量、晶格畸变、表面形貌、表面化学态和光学特性进行了表征分析。本论文的研究内容与取得的成果如下：1. 采用优化的MOCVD脉冲生长工艺,首先在蓝宝石衬底上高温生长了AlN缓冲层,进而得到了高质量的AlxGa1-xN外延薄膜,其中Al组分为0～-87%。并且系统地研究了高温AlN缓冲层对减少裂纹密度,提高晶体质量的作用。测试结果表明当高温AlN缓冲层的厚度为200 nm时,可以极大地改善AlGaN外延层的晶体质量。研究还发现：随着AlxGa1-xN薄膜中Al组分的增加,晶格发生了收缩,即晶格常数c、a以及c/a的比值均有所减小；与之相反的是内参数u的数值反而随着Al组分的增加而增大,这种变化趋势可以解释为由于Al的并入增加,Al-N键的离子化效应增强所导致的。2.采用Raman光谱研究了AlGaN薄膜中应力的变化行为。研究结果表明：AlxGa1-xN薄膜的A1(LO)模式的声子频移随Al组分的变化较为明显,并且是单模行为；而Al(LO)模式的声子频移峰的展宽推测主要源于AlxGa1-xN薄膜材料中的长程有序。通过系统地研究AlxGa1-xN薄膜的光致发光行为,对由缺陷态发光引起的黄带机制做了深入的探讨。Al0.26Ga0.74N薄膜样品的低温光致发光谱测试结果表明：随着温度的降低,由自由载流子复合引起的317 nm的带边发射峰有“蓝移”的趋势,并且温度越低,发光强度越高,峰值的半高宽也明显减小。3. 采用同步辐射技术研究了AlGaN材料的电子结构。通过分析Ga的K边延长的X射线吸收精细结构光谱(EXAFS)探究了不同壳层原子键长与Al组分的依赖关系。研究结果表明：位于第一壳层的Ga-N键长与Al组分的变化无关,其值只与离Ga原子最近的N原子相关；然而第二壳层的Ga-Ga键长与Al组分的关系较大。计算结果发现Ga-Ga键长要大于Ga-Al键长,并且随着AlxGa1-xN薄膜样品中Al组分的增加,Ga-Ga键长有减小的趋势,分析这可能与Al原子的原子半径较小有关。本论文还进一步地研究了AlxGa1-xN薄膜的表面化学态。通过测量Ga 3d、Al 2p, N Is的XPS能谱,以及对XPS能谱进行拟合,分析研究了AlxGa1-xN薄膜表面的氧化行为。结果显示：AlxGa1-xN薄膜样品表面同时存在着氮化物与氧化物,并且随着Al组分的增加,Al的氧化要强于Ga的氧化。研究还发现,Ga的俄歇跃迁与O-Ga键或者Ga的其他化合物相关。4. 探究了AlInGaN四元材料的生长工艺,系统地研究了生长温度对相分离现象的影响和富In区域形成的物理机制,优化得到较为理想的生长温度为890℃。光致发光谱测试结果表明随着生长压力的减小,缺陷杂质发光得到抑制,说明较低的生长压力会改善AlInGaN薄膜的晶体质量,发现其中的“Ⅴ”型缺陷的密度和尺寸都随着压力的降低而减小；高Al/In摩尔比会抑制AlInGaN薄膜中的相分离,可能是因为富In团簇的减少导致了这一结果。通过Raman光谱测量验证了AlInGaN四元薄膜中确实存在In的团簇,同时该结论也说明了“Ⅴ”型缺陷的来源与In的并入有很大关系。AlInGaN四元薄膜的变温光致发光谱揭示了AlInGaN发光峰峰值能量随温度的变化呈“S”形变化的关系,并对这一现象作了合理的解释。5.深入研究了AlGaN/GaN多量子阱的生长工艺条件,特别是异质结界面的H2吹扫时间对量子阱界面质量与光学性能的影响。实验发现,当生长AlGaN势垒层后的H2吹扫时间为4分钟,生长GaN阱层后H2的吹扫时间为2分钟时,可以获得界面平滑、组分变化陡峻的量子阱界面。通过对量子阱界面质量的分析,进一步探讨了量子阱中的缺陷形成机制。在此基础上,并通过优化生长工艺条件,最终制备得到了高质量、界面清晰的AlGaN/GaN多量子阱样品。光致发光谱测试结果表明,由于存在内建电场,因量子限制斯塔克效应引起的能带弯曲,导致了AlGaN/GaN多量子阱发光峰的“红移”；而当量子阱宽降低时,量子限制效应占主导地位,导致发光峰波长的“蓝移”。6.对半极性R面与非极性A面、M面蓝宝石衬底上GaN与AlGaN的外延生长工艺进行了优化。发现生长成核层时采用高的Ⅴ/Ⅲ比有利于改善GaN外延薄膜的晶体质量,但所获得的晶体为沿着c[0001]方向生长的极性材料。本研究也在非极性M面蓝宝石衬底上进行了GaN材料的生长,获得了晶体质量较好的具有[1122]晶向的半极性样品。本研究还在A面和M面蓝宝石衬底上生长了AlGaN材料,并且进行了Si掺杂。发现在A面衬底上生长的AlGaN经过Si掺杂后表面形貌和晶体质量都得到了改善,C的并入量有所减少,蓝带发光强度减弱。而在M面蓝宝石衬底上生长的AlGaN经过Si掺杂以后,表面形貌和晶体质量却有所下降,C的并入量增加,蓝带发光强度减弱。本研究所开展的半极性、非极性GaN和AlGaN材料的生长实验,为制备高亮度非极性AlGaN基紫外LED打下了坚实的基础。7. 采用APSYS光学器件模拟软件分析计算了p-AlInGaN四元材料以及p-AlInGaN/GaN超晶格结构作为GaN基LED电子阻挡层对LED芯片光电性能的影响。通过对量子阱中的极化电场以及极化场下能带结构、载流子浓度分布、自发辐射复合速率的研究,发现采用与GaN晶格匹配的p-In0.018Al0.089Ga0.893N/GaN超晶格作为电子阻挡层,不仅可以减小由于极化电场引起的能带弯曲效应,而且通过p-GaN层注入到有源区的空穴注入效率得到了很大的提高,同时漏电流也获得明显减小。并且在大电流注入条件下,研究结果表明采用p-In0.018Al0.089Ga0.893N/GaN超晶格电子阻挡层结构的GaN基LED的“效率下降”现象得到了明显的改善。
[Abstract]:AlxGa1-xN is a direct band gap wide band gap semiconductor material with stable chemical properties, high temperature resistance, radiation resistance and continuous adjustable wavelength in the range of 200~365 nm. It has a wide application prospect in the fields of air purification, sterilization and disinfection, semiconductor solid-state lighting and so on. The crystal quantity of.AlGaN films has a great influence on the photoelectric properties of the devices, especially in the preparation of UV. The growth of high A1 component AlGaN material required by LED, the design of quantum well structure and the influence of polarization effect have been the key factors that restrict the development of UV LED. Therefore, it is very important to study the growth and characterization of AlGaN thin films. This paper uses the method of chemical vapor deposition of metal organic compounds (MOCVD) to prepare the high quality. The physical properties of AlGaN materials are systematically studied with the AlGaN film of the Al component, and the physical properties of the more practical AlInGaN four element materials are grown and characterized. At the same time, the effect of AlInGaN four yuan material on improving the photoelectric properties of LED is theoretically studied. The high quality AlGaN/GaN multi quantum is prepared by optimizing the growth process. Well, a solid foundation was laid for the preparation of AlGaN based UV LED. In addition, a systematic experiment was carried out on the epitaxial growth of GaN and AlGaN based on the non polar and semi polar sapphire substrates. High resolution X ray diffraction (HR-XRD), scanning electron microscopy (SEM), photoluminescence (PL), X ray photoelectron spectroscopy (XPS), and synchrotron radiation X ray were used. The crystal quality, lattice distortion, surface morphology, surface chemical and optical properties of the epitaxial materials are characterized by spectroscopic methods. The contents and achievements of this paper are as follows: 1. the AlN buffer layer was first grown on the sapphire substrate by the optimized MOCVD pulse growth process, and the high quality was obtained. The AlxGa1-xN epitaxial film, in which the Al group is divided into 0 ~ -87%., and the effect of the high temperature AlN buffer layer on reducing the crack density and improving the crystal quality is systematically studied. The test results show that when the thickness of the high temperature AlN buffer layer is 200 nm, the crystal quality of the AlGaN epitaxial layer can be greatly improved. The study also shows that with the Al in the AlxGa1-xN thin film, the crystal quality can be greatly improved. With the increase of the component, the lattice of the lattice is contracted, that is, the ratio of the lattice constant C, a and c/a decreases. In contrast, the internal parameter u increases with the increase of the Al component. This trend can be explained by the Raman spectrum studied by Raman spectrum due to the increase of Al's incorporation and the enhancement of the ionization effect of the Al-N bond. The change of stress in the GaN film shows that the phonon shift of the A1 (LO) mode of the AlxGa1-xN film is more obvious with the change of the Al component, and it is a single mode behavior, while the broadening of the phonon frequency shift peak in the Al (LO) mode is mainly derived from the long range order in the AlxGa1-xN film material. The light of the AlxGa1-xN thin film is systematically studied. The luminescence behavior and the mechanism of the yellow band caused by the defect state luminescence have been deeply discussed. The results of low temperature photoluminescence spectrum test of.Al0.26Ga0.74N film samples show that with the decrease of temperature, the 317 nm edge emission peak caused by free carrier recombination has a "blue shift" trend, and the lower the temperature, the higher the luminescence intensity, the peak value. The electronic structure of AlGaN materials was studied by.3. by synchrotron radiation technology. The dependence of the bond length of different shell atoms and the Al component was investigated by analyzing the X ray absorption fine structure spectrum (EXAFS) of the K edge extension of Ga. The results showed that the Ga-N bond length in the first shell was independent of the Al component. Its value is only related to the N atom nearest to the Ga atom; however, the length of the Ga-Ga bond of the second shell is closely related to the Al component. The calculation results show that the length of the Ga-Ga bond is larger than the Ga-Al bond length, and the Ga-Ga bond length decreases with the increase of the Al component in the AlxGa1-xN film samples. This analysis may be related to the smaller atomic radius of the Al atom. The surface chemical state of the AlxGa1-xN film is further studied. By measuring the XPS energy spectrum of Ga 3D, Al 2p, N Is and the fitting of the XPS spectrum, the oxidation behavior of the AlxGa1-xN film surface is analyzed and studied. The results show that there is a nitride and oxide on the surface of the AlxGa1-xN film sample and the increase of the Al components. The oxidation of L is stronger than the oxidation of Ga. It is also found that the Ga's auger transition is related to the O-Ga bond or other compounds associated with Ga to explore the growth process of the AlInGaN four element material, and systematically study the effect of the growth temperature on the phase separation and the physical mechanism of the formation of the rich In region. The optimum growth temperature is 890. The results of the hair spectrum test show that with the decrease of the growth pressure, the luminescence of the defective impurities is suppressed. It shows that the lower growth pressure will improve the crystal quality of the AlInGaN film. It is found that the density and size of the "V" type defects decrease with the decrease of pressure, and the high Al/In molar ratio will inhibit the phase separation in the AlInGaN film. This result is caused by the reduction of the rich In cluster. The cluster of In in the AlInGaN four element film is verified by the Raman spectrum measurement. The conclusion also shows that the origin of the "V" type defect and the incorporation of In have a great relationship with the.AlInGaN four element thin film, which reveals the peak energy of the AlInGaN luminescence peak. The change of temperature shows a "S" shape change, and a reasonable explanation of this phenomenon is made by.5.. The growth process conditions of AlGaN/GaN multiple quantum well are deeply studied, especially the influence of H2 blowing time on the quality and optical properties of the quantum well interface at the heterojunction interface. The experiment shows that the time of H2 blowing after the growth of the AlGaN barrier layer is 4. When the blower time of the GaN well layer is 2 minutes after the growth of the well, the interface is smooth and the composition of the quantum well can be precipitous. By analyzing the quality of the quantum well interface, the formation mechanism of the defect in the quantum well is further discussed. On this basis, the high quality, the interface clear is obtained by optimizing the growth process conditions. The results of photoluminescence spectrum test show that due to the existence of the built-in electric field, the band bending caused by the quantum confinement effect leads to the "red shift" of the luminescence peak of the AlGaN/GaN multi quantum well, while the quantum confinement effect should dominate when the width of the quantum well is reduced, leading to the "blue shift" of the wavelength of the luminescence peak. ".6. has optimized the epitaxial growth process of GaN and AlGaN on the semi polar R surface and non polar A surface and M surface sapphire substrate. It is found that the high V / III ratio is beneficial to improve the crystal quality of the GaN epitaxial film when the nucleation layer is growing, but the obtained crystal is a polar material along the c[0001] direction. This study is also in the non polar M surface blue. The GaN material was grown on the gem substrate, and the crystal quality with [1122] crystal direction was obtained. The AlGaN material was grown on the A surface and the M surface sapphire substrate, and the Si doping was carried out. It was found that the surface morphology and crystal quality of AlGaN grown on the A substrate were improved after Si doping, C. The absorption of the blue band decreases and the luminescence intensity of the blue band is weakened. The surface morphology and crystal quality of the AlGaN grown on the M sapphire substrate has declined after the Si doping, and the incorporation of C is increased and the luminescence intensity of the blue band is weakened. The growth experiments of the semi polar, non polar GaN and AlGaN materials in this study are to prepare the high brightness non polar. The sexual AlGaN based UV LED lays a solid foundation.7. using APSYS optical device simulation software to analyze and calculate the effect of p-AlInGaN four yuan material and p-AlInGaN/GaN superlattice as the GaN based LED electronic barrier layer on the optoelectronic properties of LED chip. By the polarization field in the quantum well and the band structure under the polarization field, the carrier concentration Distribution, the study of the spontaneous radiation recombination rate, it is found that using the p-In0.018Al0.089Ga0.893N/GaN superlattice matched with the GaN lattice as the electronic barrier layer, it can not only reduce the band bending effect caused by the polarization electric field, but also improve the cavity injection efficiency by injecting the p-GaN layer into the active region, and the leakage current also is also improved. The results are obviously reduced and the results show that the "efficiency decline" of the GaN based LED with the structure of the p-In0.018Al0.089Ga0.893N/GaN superlattice is obviously improved under the condition of high current injection.

【学位授予单位】：东南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TN312.8

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