带有分布式布拉格反射镜的紫外LED制备研究

发布时间：2018-02-10 06:07

本文关键词： AlGaN MOCVD 分布式布拉格反射镜紫外LED　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：随着GaN基发光二极管(LED)研发的不断深入,其技术创新与应用领域也在不断拓展,以AlGaN作为有源区的紫外LED逐渐成为研究重点。AlGaN基紫外LED在固化、医疗、短距离通信等领域有重要应用价值。且相较于传统的紫外光源,具有高效节能、无汞环保、可靠耐用、体积小等优点。另外,由于分布式布拉格反射镜(DBR)可以反射特定波长的光,已被广泛应用到发光器件中以提高光提取效率。在本文中,我们分别在蓝宝石衬底和SiC衬底上开展了AlGaN基紫外DBR的制备工作,并基于SiC衬底初步研制了带有DBR的紫外LED,具体工作如下:我们从理论上计算分析了生长在蓝宝石衬底/GaN模板层上的AlxGa1-xN薄膜开裂临界厚度与Al组分x之间关系,并结合实验中外延得到的不同厚度AlGaN薄膜开裂情况与Al组分值之间的关系验证了理论计算结果的可靠性。实验上,我们利用金属有机物化学气相沉积(MOCVD)方法在蓝宝石衬底上制备AlGaN/GaN DBR,通过引入低温AlN插入层调控薄膜内应力,获得了无裂纹的AlGaN/GaN DBR。我们又研究了Al N插入层对DBR特性的影响,发现低温AlN插入层的引入在防止裂纹产生的同时会引起外延层表面平整度退化,这可能是由不平整的低温AlN插入层表面造成的。随着DBR对数的增加,其表面平整度得到逐步改善。经过系列实验,我们在蓝宝石衬底上制备得到了中心波长在390 nm,峰值反射率为94%,阻带宽度16 nm的25对无裂纹Al0.32Ga0.68N/GaN DBR,其表面粗糙度为0.46nm。为下一步研制带有DBR的近紫外LED奠定了基础。相比于蓝宝石衬底,SiC衬底与AlGaN晶格失配小,可有效改善AlGaN外延层晶体质量。同时,SiC衬底良好的导电性能使其可以被用来外延制备垂直导电结构LED,与水平结构相比垂直结构LED可以有效解决电流拥堵现象,提高有源区利用率。我们在n型6H-SiC衬底上制备了Si掺杂AlGaN基DBR,通过引入低温AlN模板层,获得了表面均方根粗糙度为0.4 nm且导电性能良好的15对无裂纹n型Al0.19Ga0.81N/Al0.37Ga0.63N DBR,其在369 nm处峰值反射率为68%,阻带宽度为10 nm。在获得导电DBR的基础上,我们进一步在n型6H-SiC衬底上构建了有、无DBR的垂直结构紫外LED。对比两者电致发光光谱,发现DBR结构的引入可以明显增强LED紫外发光强度。
[Abstract]:With the development of GaN based LED, its technology innovation and application fields are also expanding. Ultraviolet LED with AlGaN as its active region is becoming the focus of research. AlGaN-based UV LED is solidified and treated. Short distance communication and other fields have important application value. Compared with traditional ultraviolet light sources, they have the advantages of high efficiency, energy saving, no mercury, environmental protection, reliability, durability, small size, etc. Distributed Bragg reflector (DBR) can reflect light of specific wavelength, so it has been widely used in light-emitting devices to improve the efficiency of optical extraction. We have prepared AlGaN based UV DBR on sapphire and SiC substrates, respectively. Based on SiC substrate, UV LED with DBR has been developed. The main work is as follows: we calculated and analyzed the relationship between critical cracking thickness of AlxGa1-xN film grown on sapphire substrate / gan template layer and Al component x. The reliability of the calculated results is verified by the relationship between the cracking of AlGaN thin films with different thickness and the Al component in the experiment. AlGaN/GaN DBRs were prepared on sapphire substrates by metal-organic chemical vapor deposition (MOCVD) method. The crack free AlGaN/GaN DBRs were obtained by introducing a low temperature AlN intercalation layer to regulate the internal stress of the films. We also studied the effect of the AlN intercalation layer on the DBR properties. It is found that the introduction of the low temperature AlN intercalation layer can not only prevent the formation of cracks, but also cause the degradation of the surface smoothness of the epitaxial layer, which may be caused by the uneven low temperature AlN intercalation layer surface. With the increase of the DBR logarithm, Its surface smoothness has been gradually improved. After a series of experiments, We have prepared on sapphire substrates 25 pairs of crack-free Al0.32Ga0.68N/GaN DBRs with a central wavelength of 390nm, a peak reflectivity of 94nm and a stopband width of 16nm, the surface roughness of which is 0.46nm. this will lay a foundation for the next development of near-ultraviolet LED with DBR. The lattice mismatch between sic substrate and AlGaN substrate is smaller than that on sapphire substrate. The crystal quality of AlGaN epitaxial layer can be improved effectively. At the same time, sic substrate can be used to epitaxially fabricate vertical conductive structure. Compared with horizontal structure, vertical structure LED can effectively solve the problem of current congestion. We prepared Si-doped AlGaN based DBRs on n-type 6H-SiC substrates by introducing low temperature AlN template layer. Fifteen pairs of crack free n-mode Al0.19Ga0.81N/Al0.37Ga0.63N DBRs with a surface RMS roughness of 0.4 nm and good conductivity were obtained. The peak reflectivity at 369 nm was 68 and the stopband width was 10 nm. On the basis of obtaining conductive DBR, We have further constructed the vertical structure LED with and without DBR on n-type 6H-SiC substrates. Compared with the electroluminescent spectra, it is found that the introduction of DBR structure can obviously enhance the UV luminescence intensity of LED.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN312.8

【参考文献】