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      Energy relaxations of hot electrons in AlGaN/AlN/GaN heterostructures grown by MOCVD on sapphire and 6H-SiC substrates

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      Author
      Ilgaz, A.
      Gökden, S.
      Tülek, R.
      Teke, A.
      Özçelik, S.
      Özbay, Ekmel
      Date
      2011-08-18
      Source Title
      The European Physical Journal Applied Physics
      Print ISSN
      1286-0042
      Publisher
      E D P Sciences
      Volume
      55
      Issue
      3
      Pages
      30102- 1 - 30102- 6
      Language
      English
      Type
      Article
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      Abstract
      In this work, we investigated the hot-electron dynamics of AlGaN/GaN HEMT structures grown by MOCVD on sapphire and SiC substrates at 80 K. High-speed current-voltage measurements and Hall measurements over the temperature range 27-300 K were used to study hot-electron dynamics. At low fields, drift velocity increases linearly, but deviates from the linearity toward high electric fields. Drift velocities are deduced as approximately 6.55 × 10 6 and 6.60 × 106 cm/s at an electric field of around E ∼ 25 kV/cm for samples grown on sapphire and SiC, respectively. To obtain the electron temperature as a function of the applied electric field and power loss as a function of the electron temperature, we used the so-called mobility comparison method with power balance equations. Although their low field carrier transport properties are similar as observed from Hall measurements, hot carrier energy dissipation differs for samples grown on sapphire and SiC substrates. We found that LO-phonon lifetimes are 0.50 ps and 0.32 ps for sapphire and SiC substrates, respectively. A long hot-phonon lifetime results in large non- equilibrium hot phonons. Non-equilibrium hot phonons slow energy relaxation and increase the momentum relaxation. The effective energy relaxation times at high fields are 24 and 65 ps for samples grown on sapphire and SiC substrates, respectively. They increase as the electron temperature decreases.
      Keywords
      AlGaN/AlN/GaN
      AlGaN/GaN HEMTs
      Applied electric field
      Comparison methods
      Current-voltage measurements
      Drift velocities
      Effective energy
      Energy relaxation
      Hall measurements
      High electric fields
      Permalink
      http://hdl.handle.net/11693/21787
      Published Version (Please cite this version)
      http://dx.doi.org/10.1051/epjap/2011110218
      Collections
      • Department of Electrical and Electronics Engineering 3524
      • Department of Physics 2299
      • Nanotechnology Research Center (NANOTAM) 1006
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