圖形化藍寶石襯底上LED外延的形核機理及襯底圖案設計
發(fā)布時間：2019-05-08 22:25
【摘要】：隨著能源危機的加劇,低能源消耗的發(fā)展模式日益受到重視。在照明領域,LED作為新一代固態(tài)照明源,符合節(jié)能減排的發(fā)展要求,但目前仍有難題亟待攻破。一來,用于異質外延的藍寶石襯底與GaN外延薄膜存在巨大的晶格失配和熱膨脹差異,導致外延層存在大量缺陷,非輻射復合中心增多,LED的內(nèi)量子效率下降;二來,LED芯片材料折射率遠高于外部空氣,使得有源區(qū)產(chǎn)生的光線在芯片與空氣的界面處發(fā)生顯著的全反射,光線透射出芯片表面的幾率低,LED的光提取效率降低。針對上述難題,近期發(fā)展的圖形化藍寶石襯底技術(Patterned Sapphire Substrate,PSS)顯示了很好的優(yōu)勢,但技術瓶頸仍然突出。論文總結了目前圖形化藍寶石襯底技術存在的難題,并圍繞技術難題開展基礎研究。分階段觀察半球形圖案PSS上GaN外延的形核過程,研究了PSS促進GaN橫向生長的原因。研究表明GaN島狀生長階段的奧斯特瓦爾德熟化過程是PSS加速薄膜愈合的關鍵。圖案溝壑處的GaN小島不斷吞噬圖案頂部的GaN團簇而成為薄膜生長的“主力軍”,加之有序排布的圖案為GaN小島生長提供相同的外部環(huán)境,GaN小島能在同一時間全方位覆蓋圖案,改善薄膜均勻性,從而縮短薄膜愈合周期。與平面藍寶石襯底上的GaN外延相比,相同生長條件下PSS上外延的GaN薄膜厚度增加12%。論文在上述研究基礎上,在半球形圖案PSS上生長完整的LED外延結構,通過觀察外延結構的微觀缺陷,結合GaN外延形核過程,揭示PSS改善LED外延薄膜晶體質量的內(nèi)因。研究發(fā)現(xiàn)PSS對薄膜位錯的抑制主要來自堆垛層錯的阻擋和薄膜生長模式的誘導。一方面,PSS誘發(fā)堆垛層錯在圖案頂部形成,阻擋了來自圖案處的位錯攀移;另一方面,PSS促使GaN橫向生長,在橫向生長模式的帶動下,圖案溝壑處衍生的位錯有隨薄膜的橫向生長而彎曲的傾向。最終位錯更少地攀移至量子阱層,改善了LED外延薄膜的晶體質量。針對PSS的設計難題,論文提出了基于TracePro的圖案設計手段,并得到了實驗結果的有力驗證。應用該圖案設計方法,論文研究了底寬大于3μm、高度大于1.6μm的大尺寸圓錐圖案PSS的出光效果,獲得光提取效果優(yōu)于常用PSS的大尺寸圓錐圖案PSS。對模擬的大尺寸圓錐圖案PSS進行制備和LED外延,分析了大尺寸圓錐圖案PSS對光散射、薄膜晶體質量、薄膜應力的影響。與目前商用的PSS-LED相比,設計的大尺寸圓錐圖案PSS-LED的光輸出功率提升12.7%。綜上,論文從微觀尺度分析了PSS上LED外延的形核機理,并提出了圖案設計的新方法。論文將對PSS上高質量LED外延薄膜的生長提供理論指導,對設計、制備高效PSS-LED提供技術支撐。
[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.
【學位授予單位】：華南理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TN312.8
本文編號：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.
【學位授予單位】：華南理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TN312.8
【參考文獻】
相關期刊論文 前2條
1 顏建;鐘燦濤;于彤軍;徐承龍;陶岳彬;張國義;;圖形化藍寶石襯底上InGaN/GaN多量子阱發(fā)光二極管的光譜特性研究[J];光譜學與光譜分析;2012年01期
2 王恩哥;薄膜生長中的表面動力學(Ⅰ)[J];物理學進展;2003年01期
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