Optical phonons and free-carrier effects in MOVPE grown Al x Ga 1-x N measured by Infrared Ellipsometry
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Optical phonons and free-carrier effects in MOVPE grown AlxGa1−xN measured by Infrared Ellipsometry M. Schubert, A. Kasic, T.E. Tiwald, J. Off, B. Kuhn and Ferdinand Scholz MRS Internet Journal of Nitride Semiconductor Research / Volume 4 / Issue 01 / January 1999 DOI: 10.1557/S1092578300000673, Published online: 13 June 2014
Link to this article: http://journals.cambridge.org/abstract_S1092578300000673 How to cite this article: M. Schubert, A. Kasic, T.E. Tiwald, J. Off, B. Kuhn and Ferdinand Scholz (1999). Optical phonons and free-carrier effects in MOVPE grown AlxGa1−xN measured by Infrared Ellipsometry . MRS Internet Journal of Nitride Semiconductor Research, 4, pp e11 doi:10.1557/S1092578300000673 Request Permissions : Click here
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MRS
Internet Journal Nitride Semiconductor Research
Optical phonons and free-carrier effects in MOVPE grown AlxGa1-xN measured by Infrared Ellipsometry M. Schubert1, A. Kasic1, T.E. Tiwald1, J. Off2, B. Kuhn2 and Ferdinand Scholz2 1Center for Microelectronic and Optical Materials Research and Department of Electrical Engineering, University of Nebraska-Lincoln, 24. Physikalisches Institut, Universität Stuttgart,
(Received Tuesday, August 24, 1999; accepted Wednesday, September 29, 1999)
We report on the application of infrared spectroscopic ellipsometry (IR-SE) for wavenumbers from 333cm-1 to 1200cm-1 as a novel approach to non-destructive optical characterization of free-carrier and optical phonon properties of group III-nitride heterostructures. Undoped α-GaN, α-AlN, αAlxGa1-xN (x = 0.17, 0.28, 0.5), and n-type silicon (Si) doped α-GaN layers were grown by metalorganic vapor phase epitaxy (MOVPE) on c-plane sapphire (α-Al2O3). The four-parameter semiquantum (FPSQ) dielectric lattice-dispersion model and the Drude model for free-carrier response are employed for analysis of the IR-SE data. Model calculations for the ordinary (∈⊥) and extraordinary (∈||) dielectric functions of the heterostructure components provide sensitivity to IRactive phonon frequencies and free-carrier parameters. We observe that the α-AlxGa1-xN layers are unintentionally doped with a back ground free-carrier concentration of 1–4 1018cm-3. The ternary compounds reveal a two-mode behavior in ∈⊥, whereas a one-mode behavior is sufficient to explain the optical response for ∈||. We further provide a precise set of model parameters for calculation of the sapphire infrared dielectric functions which are prerequisites for analysis of infrared spectra of III-nitride heterostructures grown on α-Al2O3.
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Introduction
The wide band gap semiconductor systems of the group III-nitrides have gained considerable interest because of their potential application for optoelectronic devices covering the visible (VIS) spectrum with extension to near-ultraviolet (UV) wav
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