图形化蓝宝石衬底上LED外延的形核机理及衬底图案设计
发布时间：2019-05-08 22:25
【摘要】：随着能源危机的加剧,低能源消耗的发展模式日益受到重视。在照明领域,LED作为新一代固态照明源,符合节能减排的发展要求,但目前仍有难题亟待攻破。一来,用于异质外延的蓝宝石衬底与GaN外延薄膜存在巨大的晶格失配和热膨胀差异,导致外延层存在大量缺陷,非辐射复合中心增多,LED的内量子效率下降;二来,LED芯片材料折射率远高于外部空气,使得有源区产生的光线在芯片与空气的界面处发生显著的全反射,光线透射出芯片表面的几率低,LED的光提取效率降低。针对上述难题,近期发展的图形化蓝宝石衬底技术(Patterned Sapphire Substrate,PSS)显示了很好的优势,但技术瓶颈仍然突出。论文总结了目前图形化蓝宝石衬底技术存在的难题,并围绕技术难题开展基础研究。分阶段观察半球形图案PSS上GaN外延的形核过程,研究了PSS促进GaN横向生长的原因。研究表明GaN岛状生长阶段的奥斯特瓦尔德熟化过程是PSS加速薄膜愈合的关键。图案沟壑处的GaN小岛不断吞噬图案顶部的GaN团簇而成为薄膜生长的“主力军”,加之有序排布的图案为GaN小岛生长提供相同的外部环境,GaN小岛能在同一时间全方位覆盖图案,改善薄膜均匀性,从而缩短薄膜愈合周期。与平面蓝宝石衬底上的GaN外延相比,相同生长条件下PSS上外延的GaN薄膜厚度增加12%。论文在上述研究基础上,在半球形图案PSS上生长完整的LED外延结构,通过观察外延结构的微观缺陷,结合GaN外延形核过程,揭示PSS改善LED外延薄膜晶体质量的内因。研究发现PSS对薄膜位错的抑制主要来自堆垛层错的阻挡和薄膜生长模式的诱导。一方面,PSS诱发堆垛层错在图案顶部形成,阻挡了来自图案处的位错攀移;另一方面,PSS促使GaN横向生长,在横向生长模式的带动下,图案沟壑处衍生的位错有随薄膜的横向生长而弯曲的倾向。最终位错更少地攀移至量子阱层,改善了LED外延薄膜的晶体质量。针对PSS的设计难题,论文提出了基于TracePro的图案设计手段,并得到了实验结果的有力验证。应用该图案设计方法,论文研究了底宽大于3μm、高度大于1.6μm的大尺寸圆锥图案PSS的出光效果,获得光提取效果优于常用PSS的大尺寸圆锥图案PSS。对模拟的大尺寸圆锥图案PSS进行制备和LED外延,分析了大尺寸圆锥图案PSS对光散射、薄膜晶体质量、薄膜应力的影响。与目前商用的PSS-LED相比,设计的大尺寸圆锥图案PSS-LED的光输出功率提升12.7%。综上,论文从微观尺度分析了PSS上LED外延的形核机理,并提出了图案设计的新方法。论文将对PSS上高质量LED外延薄膜的生长提供理论指导,对设计、制备高效PSS-LED提供技术支撑。
[Abstract]:With the aggravation of energy crisis, the development mode of low energy consumption has been paid more and more attention. In the lighting field, as a new generation solid-state illumination source, LED accords with the development requirements of energy saving and emission reduction, but there are still some problems to be solved. First, there is a great difference in lattice mismatch and thermal expansion between the sapphire substrate used for heteroepitaxial epitaxy and the GaN epitaxial film, resulting in a large number of defects in the epitaxial layer, the increase of the non-radiative recombination centers and the decrease of the internal quantum efficiency of LED. Secondly, the refractive index of the LED chip material is much higher than that of the external air, which makes the light generated in the active region reflect significantly at the interface between the chip and the air, and the probability of light transmission from the chip surface is low, and the efficiency of LED light extraction is reduced. In response to the above problems, the recent development of graphic sapphire substrate technology (Patterned Sapphire Substrate,PSS) shows good advantages, but the technical bottleneck is still prominent. In this paper, the existing problems of graphic sapphire substrate technology are summarized, and the basic research is carried out around the technical problems. The nucleation process of GaN epitaxial growth on hemispherical pattern PSS was observed in stages, and the reason why PSS promoted the transverse growth of GaN was studied. The results show that the Ostwald ripening process in the island growth stage of GaN is the key to accelerate the healing of PSS thin films. The island of GaN in the gully region continues to devour the GaN cluster at the top of the pattern and become the "main force" for thin film growth. In addition, the orderly arrangement of the pattern provides the same external environment for the growth of the island of GaN, and the island of GaN can cover the pattern in all directions at the same time. Improve the uniformity of the film, thus shorten the healing period of the film. Compared with GaN epitaxial on planar sapphire substrate, the thickness of GaN thin film grown on PSS increases by 12% under the same growth conditions. On the basis of the above research, the complete LED epitaxial structure was grown on the hemispherical pattern PSS. By observing the micro-defects of the epitaxial structure and combining with the nucleation process of the GaN epitaxy, the internal cause of the improvement of the crystal quality of the LED epitaxial film by PSS was revealed. It is found that the inhibition of dislocation caused by PSS is mainly due to the barrier of stacking fault and the induction of thin film growth mode. On the one hand, PSS induces stacking fault formation at the top of the pattern, blocking dislocation climbing from the pattern; On the other hand, PSS promotes the transverse growth of GaN. Under the drive of the transverse growth mode, the dislocation derived from the pattern gully tends to bend with the transverse growth of the film. The final dislocation moves to the quantum well layer less, which improves the crystal quality of LED epitaxial films. Aiming at the difficult problem of PSS design, this paper proposes a pattern design method based on TracePro, and gets the strong verification of the experimental results. Using this pattern design method, this paper studies the light output effect of the large size cone pattern PSS with the base width greater than 3 渭 m and the height greater than 1.6 渭 m. The result shows that the light extraction effect of the large size cone pattern PSS. is better than that of the common PSS cone pattern. The simulated large-size cone pattern PSS was fabricated and LED epitaxial was used to analyze the effects of large-size cone pattern PSS on light scattering, crystal quality and film stress. Compared with the commercial PSS-LED, the optical output power of the large-size conical pattern PSS-LED is increased by 12.7%. In this paper, the nucleation mechanism of LED epitaxy on PSS is analyzed from the micro-scale, and a new method of pattern design is put forward. This paper will provide theoretical guidance for the growth of high-quality LED epitaxial films on PSS and technical support for the design and preparation of high-efficiency PSS-LED films.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN312.8
本文编号：2472266
[Abstract]:With the aggravation of energy crisis, the development mode of low energy consumption has been paid more and more attention. In the lighting field, as a new generation solid-state illumination source, LED accords with the development requirements of energy saving and emission reduction, but there are still some problems to be solved. First, there is a great difference in lattice mismatch and thermal expansion between the sapphire substrate used for heteroepitaxial epitaxy and the GaN epitaxial film, resulting in a large number of defects in the epitaxial layer, the increase of the non-radiative recombination centers and the decrease of the internal quantum efficiency of LED. Secondly, the refractive index of the LED chip material is much higher than that of the external air, which makes the light generated in the active region reflect significantly at the interface between the chip and the air, and the probability of light transmission from the chip surface is low, and the efficiency of LED light extraction is reduced. In response to the above problems, the recent development of graphic sapphire substrate technology (Patterned Sapphire Substrate,PSS) shows good advantages, but the technical bottleneck is still prominent. In this paper, the existing problems of graphic sapphire substrate technology are summarized, and the basic research is carried out around the technical problems. The nucleation process of GaN epitaxial growth on hemispherical pattern PSS was observed in stages, and the reason why PSS promoted the transverse growth of GaN was studied. The results show that the Ostwald ripening process in the island growth stage of GaN is the key to accelerate the healing of PSS thin films. The island of GaN in the gully region continues to devour the GaN cluster at the top of the pattern and become the "main force" for thin film growth. In addition, the orderly arrangement of the pattern provides the same external environment for the growth of the island of GaN, and the island of GaN can cover the pattern in all directions at the same time. Improve the uniformity of the film, thus shorten the healing period of the film. Compared with GaN epitaxial on planar sapphire substrate, the thickness of GaN thin film grown on PSS increases by 12% under the same growth conditions. On the basis of the above research, the complete LED epitaxial structure was grown on the hemispherical pattern PSS. By observing the micro-defects of the epitaxial structure and combining with the nucleation process of the GaN epitaxy, the internal cause of the improvement of the crystal quality of the LED epitaxial film by PSS was revealed. It is found that the inhibition of dislocation caused by PSS is mainly due to the barrier of stacking fault and the induction of thin film growth mode. On the one hand, PSS induces stacking fault formation at the top of the pattern, blocking dislocation climbing from the pattern; On the other hand, PSS promotes the transverse growth of GaN. Under the drive of the transverse growth mode, the dislocation derived from the pattern gully tends to bend with the transverse growth of the film. The final dislocation moves to the quantum well layer less, which improves the crystal quality of LED epitaxial films. Aiming at the difficult problem of PSS design, this paper proposes a pattern design method based on TracePro, and gets the strong verification of the experimental results. Using this pattern design method, this paper studies the light output effect of the large size cone pattern PSS with the base width greater than 3 渭 m and the height greater than 1.6 渭 m. The result shows that the light extraction effect of the large size cone pattern PSS. is better than that of the common PSS cone pattern. The simulated large-size cone pattern PSS was fabricated and LED epitaxial was used to analyze the effects of large-size cone pattern PSS on light scattering, crystal quality and film stress. Compared with the commercial PSS-LED, the optical output power of the large-size conical pattern PSS-LED is increased by 12.7%. In this paper, the nucleation mechanism of LED epitaxy on PSS is analyzed from the micro-scale, and a new method of pattern design is put forward. This paper will provide theoretical guidance for the growth of high-quality LED epitaxial films on PSS and technical support for the design and preparation of high-efficiency PSS-LED films.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN312.8
【参考文献】
相关期刊论文 前2条
1 颜建;钟灿涛;于彤军;徐承龙;陶岳彬;张国义;;图形化蓝宝石衬底上InGaN/GaN多量子阱发光二极管的光谱特性研究[J];光谱学与光谱分析;2012年01期
2 王恩哥;薄膜生长中的表面动力学(Ⅰ)[J];物理学进展;2003年01期
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