Threshold Voltage Engineering in GaN-Based HFETs: A Systematic Study With the Threshold Voltage Reaching More Than 2 V
M. Feneberg1, M. Winkler1, J. Klamser1, J. Stellmach2, M. Frentrup2, S. Ploch2, F. Mehnke2, T. Wernicke2, M. Kneissl2,3, and R. Goldhahn1
Published in:
Appl. Phys. Lett., vol. 106, no. 18, pp. 182102 (2015).
Abstract:
The valence band order of AlxGa1-xN is investigated experimentally by analyzing the anisotropic dielectric functions of semipolar (1122) AlGaN thin films grown on m-plane Al2O3. Point-by-point fitted dielectric functions are obtained by spectroscopic ellipsometry and corresponding inter-band transition energies are extracted. The known strain situation of the sample layers is used to correct for the small strain-induced energy shifts within k ⋅ p perturbation theory. It also is used to identify transitions related to the three valence bands. Transitions with E ⊥ c from the Γ9 valence band verify an inter-band bowing parameter of b = 0.9 eV. The transitions with E || c allow determining the crystal field splitting energy which can be described by a linear interpolation between the values for GaN and AlN satisfactorily.
1 Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany
2 Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr. 30, 10623 Berlin, Germany
3 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany
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