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URN etd-0728109-122631
Author Ming-Horng Gau
Author's Email Address d932030005@student.nsysu.edu.tw
Statistics This thesis had been viewed 5350 times. Download 1918 times.
Department Physics
Year 2008
Semester 2
Degree Ph.D.
Type of Document
Language English
Title Growth and characterizations of AlGaN/GaN HEMT structure for spintronic application
Date of Defense 2009-06-26
Page Count 76
Keyword
  • GaN
  • AlGaN
  • 2DEG
  • MOVPE
  • MBE
  • HEMT
  • SdH
  • spin-splitting
  • spintronics
  • LCAO
  • Abstract The design, fabrication, and characterizations of the spin-polarized AlxGa1-xN/GaN HEMT structure have been achieved for spintronic application. By band calculation within linear combination of atomic orbitals and two-band k·p methods, the theoretical spin-splitting energy and minimum-spin-splitting surface of wurtzite structure have been investigated as a function of the Fermi wavevector with various strain-relaxations. Base on these results, the design of host material of the nonballistic spin-FET has also been proposed. By optimizing the Al composition and n2DEG, the Fermi surface of two-dimensional electron gas is supposed to reach the minimum-spin-splitting surface to produce resonant spin-lifetime.
    Because the high quality AlxGa1-xN/GaN HEMT structure is necessary for realizing the spin-FET, the influence of the growth conditions on the polarity and structure quality of the GaN epilayer have been studied on the sample grown by plasma-assisted molecular beam epitaxy. Ga-polar AlGaN/GaN heterostructures on c-Al2O3 has been realized by growing over the Al-rich AlN nucleation layer. And the reduction of interface roughness and threading dislocation scatterings of the electrons in two-dimensional electron gas has also been achieved by growing GaN epilayer under slightly Ga-rich condition. Furthermore, the effect of different types of threading dislocation on the electron mobility of the AlxGa1-xN/GaN HEMT structure has been investigated as well. At low temperature, the electron mobility of two-dimensional electron gas in AlGaN/GaN heterostructures is majorly scattered by the edge type dislocation rather than the screw type.
    The designs of proposed host material for spin-FETs have been realized through growing high quality spin-polarized AlxGa1-xN/GaN HEMT structures with various Al composition (x= 0.191 – 0.397) grown on c-Al2O3 by metalorganic vapor phase epitaxy. The high mobility (10682 cm2/Vs at 0.4 K), flat interface (surface roughness < 0.5 nm), and high quality HEMT provide a good environment to study the spin-splitting energy. To investigate the spin-splitting energy as functions of the Fermi wavevector, the Shubnikov-de Haas measurements were performed. A large spin-splitting energy (10.76 meV) has been fabricated in Al0.390Ga0.61N/GaN HEMT structure with kf = 8.14 × 108 m-1 for the host material of the Datta-Das spin-FET. And for the first time, the minimum-spin-splitting surface has been experimentally generated in Al0.390Ga0.61N/GaN HEMT structure with kf = 8.33 × 108 m-1 for the host material of the nonballistic spin-FET.
    Advisory Committee
  • Jih-Chen Chiang - chair
  • Ming-Chi Chou - co-chair
  • Yan-Ten Lu - co-chair
  • Yan-Ten Lu - co-chair
  • K. Y. Hsieh - co-chair
  • K. Y. Hsieh - co-chair
  • Ikai Lo - advisor
  • Files
  • etd-0728109-122631.pdf
  • indicate accessible in a year
    Date of Submission 2009-07-28

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