Polarity selection mechanism of III-nitride semiconductor epitaxial films

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K04933
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 29020:Thin film/surface and interfacial physical properties-related
• Research Institution: Tohoku University
• Principal Investigator: Hanada Takashi 東北大学, 金属材料研究所, 助教 (80211481)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 窒化物半導体 / 極性 / エピタキシャル成長 / 表面構造

Outline of Final Research Achievements

The polarity of GaN crystal has been identified by X-ray diffraction using X-ray with an energy slightly higher than the absorption edge at which the most inner-shell electrons of Ga are excited. Next, by using the crystal-truncation-rod X-ray scattering measurements, the surface atomic structure of the cleavage surface of ScAlMgO4, which can be a lattice matching growth substrate of GaN, was analyzed. It was found that there is oxygen deficiency on the ScAlMgO4 cleavage surface under a reducing atmosphere. The Ga polarity selection mechanism on this substrate was proposed based on this result. Lastly, a growth model of N-polar group-III nitrides was proposed based on thermodynamics and statistical physics. The measured growth rates of an NTT group were reproduced by this model using realistic parameters, which depend on the experimental growth temperature and the flow rates of the source and carrier gases.

Free Research Field

表面界面

Academic Significance and Societal Importance of the Research Achievements

ウルツ鉱型結晶構造を持つ窒化物半導体は陰イオンとなる窒素層と陽イオンとなるIII族層が交互に積層しており、陰・陽イオンの局所的な重心の微妙なずれにより積層方向に内部電界が生じる。結晶の表裏が反転したGa極性面とN極性面では、この内部電界の向きが逆転するため、それに応じてデバイス構造を最適化する自由度ができる。従来平坦な成長表面が得やすいGa極性面が用いられてきたが、N極性面成長の改善により、第5世代移動通信に利用できる高電子移動度トランジスタでN極性がGa極性を凌ぐ特性を持つことが報告されている。本研究では極性の判定法、極性選択機構の解明、N極性成長の平坦性の改善などにつながる成果を得た。