Optical phonons and free-carrier effects in MOVPE grown Al xGa 1-xN measured by infrared ellipsometry

M. Schubert, A. Kasic, T. E. Tiwald, J. Off, B. Kuhn, Ferdinand Scholz

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Abstract

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, αAl xGa 1-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-Al 2O 3). 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-Al xGa 1-x layers are unintentionally doped with a back ground free-carrier concentration of 1-4 10 18cm -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-Al 2O 3.

Original languageEnglish (US)
JournalMRS Internet Journal of Nitride Semiconductor Research
Volume4
StatePublished - Dec 1 1999

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Metallorganic vapor phase epitaxy
Ellipsometry
Phonons
Infrared radiation
Heterojunctions
Spectroscopic ellipsometry
Aluminum Oxide
Sapphire
Nitrides
Silicon
Carrier concentration

ASJC Scopus subject areas

  • Materials Science(all)

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Optical phonons and free-carrier effects in MOVPE grown Al xGa 1-xN measured by infrared ellipsometry. / Schubert, M.; Kasic, A.; Tiwald, T. E.; Off, J.; Kuhn, B.; Scholz, Ferdinand.

In: MRS Internet Journal of Nitride Semiconductor Research, Vol. 4, 01.12.1999.

Research output: Contribution to journalArticle

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AU - Kasic, A.

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AU - Off, J.

AU - Kuhn, B.

AU - Scholz, Ferdinand

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