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JOURNAL OF APPLIED PHYSICS
Volume 87, Issue 7, Pages 3375-3380Publisher
AMER INST PHYSICS
DOI: 10.1063/1.372353
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We report on the growth of nominally undoped GaN/AlxGa1-xN/GaN (x < 0.4) high mobility heterostructures with N-face or Ga-face polarity on sapphire substrates by plasma-induced molecular beam epitaxy (PIMBE) and metalorganic chemical vapor deposition in order to study the formation and electrical transport properties of polarization induced two-dimensional electron gases (2DEGs). By depositing a thin AlN nucleation layer on the sapphire substrates before the growth of a GaN buffer layer by PIMBE, we were able to change the polarity of the wurtzite films from N to Ga face. The switch in the polarity causes a change in the sign of the spontaneous and piezoelectric polarization directed along the c axis of the strained AlGaN barrier. As a consequence the polarization induced 2DEG is confined at different interfaces in heterostructures with different polarities. The transport properties of the 2DEGs in Ga- and N-face heterostructures were investigated by a combination of capacitance-voltage profiling, Hall effect, and Shubnikov-de Haas measurements. Dominant electron scattering mechanisms are studied in order to provide the knowledge necessary for further improvements of the electron transport properties and performance of AlGaN/GaN based normal (based on Ga-face heterostructures) and inverted (based on N-face heterostructures) high electron mobility transistors. (C) 2000 American Institute of Physics. [S0021-8979(00)03007-3].
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