TY - JOUR
T1 - Optical phonons and free-carrier effects in MOVPE grown Al xGa1-xN measured by infrared ellipsometry
AU - Schubert, M.
AU - Kasic, A.
AU - Tiwald, T. E.
AU - Off, J.
AU - Kuhn, B.
AU - Scholz, Ferdinand
N1 - Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 1999
Y1 - 1999
N2 - 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-AIM, 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 IR-active phonon frequencies and free-carrier parameters. We observe that the α-AlxGa 1-x 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.
AB - 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-AIM, 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 IR-active phonon frequencies and free-carrier parameters. We observe that the α-AlxGa 1-x 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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U2 - 10.1557/s1092578300000673
DO - 10.1557/s1092578300000673
M3 - Article
AN - SCOPUS:84862400503
VL - 4
JO - MRS Internet Journal of Nitride Semiconductor Research
JF - MRS Internet Journal of Nitride Semiconductor Research
SN - 1092-5783
ER -