成果報告書詳細
管理番号20130000000877
タイトル*平成24年度中間年報 次世代高効率・高品質照明の基盤技術開発 LED照明の高効率・高品質化に係る基盤技術開発 窒化物等結晶成長手法の高度化に関する基盤技術開発(1)
公開日2013/10/18
報告書年度2012 - 2012
委託先名株式会社イノベーション・センター 国立大学法人大阪大学 国立大学法人名古屋大学
プロジェクト番号P09024
部署名電子・材料・ナノテクノロジー部
和文要約
英文要約Title:(FY2012-FY2013) FY2012 Annual Report "GaN-base high efficiency and high quality LED lighting"

In the last year, extremely low-dislocation GaN crystals could be grown on "GaN point seed" by the Na flux method, which allows the elimination of dislocations propagating from a seed layer by necking technique. However, growth of large-diameter GaN crystals remains an issue. In order to fabricate larger GaN crystals with extremely low dislocation density, we have grown GaN crystals via coalescence of GaN crystals grown on isolated point seeds and obtained a free-standing GaN crystal with the size of 1-inch. In this year, we have tried the coalescence growth of 2-inch GaN wafers with large radius of curvature.
Two-inch multi-point seeds substrate was fabricated by the chemical etching of a commercially available 2-inch c-GaN template (5 ~ 10 m-thick c-GaN layer on sapphire). After the Na-flux growth on the multi-point seeds substrate, the sapphire substrate was naturally separated from the grown crystal, leading to the 2-inch GaN substrate without cracks. X-ray diffraction measurements showed that the radius of curvature of the GaN template was 4.4 m, while that of the multi-point seeds and the grown GaN substrate was over 100 m. These results could be considered as follows. Low radius of curvature of the GaN template results from the difference of thermal expansion coefficient between the GaN layer and the sapphire substrate. When the GaN template was converted to the multi-point seeds, the strain could be released, resulting in a large radius of curvature of the multi-point seeds substrate. And then, the coalesced GaN crystal grown on such multi-point seed substrate by Na-flux method seemed to have a large radius of curvature.
From these results in this year, it was concluded that the coalescence growth on the multi-point seeds substrate is extremely useful for fabricating large-diameter GaN substrates without dislocations and strains.
LED wafer grown on GaN substrate was diced with the inclined blade, by which slanted side walls were formed. Light extraction efficiency improved two times compared with the chip diced by the conventional square blade.
In-situ X-ray CTR measurement was performed to clarify the interface flatness of InGaN quantum well and GaN barrier. Two monolayers GaN cap before the increase of the temperature for barrier growth is very effective to realize atomically flat InGaN/GaN interface.
Density of stacking fault is found to be dependent on the substrate temperature during growth and not related to the In flux. PL i9ntegrated intensity of InGaN nanowire is strongly dependent on the density of stacking fault.
Flow channel was changed from graphite to quartz, by which parasitic decomposition of metalorganic sources were much reduced. In incorporation rate and growth rate was much improved.
LEDs emitting different emission wavelengths were fabricated on Na-flux-grown (0001) GaN substrates. Internal quantum efficiency(IQE) is much improved compared with whose grown on sapphire substrates. IQE of green LED reached 60%, showing the potential of the realization of 200lm/W and CRI 80.
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