M. Schubert, A. Kasic, T.E. Tiwald
Center for Microelectronic and Optical Materials Research and Department of Electrical Engineering, University of Nebraska-Lincoln
J. Off, B. Kuhn, Ferdinand Scholz
4. Physikalisches Institut, Universität Stuttgart
-GaN,
-AlN,
-AlxGa1-xN (x = 0.17,
0.28, 0.5), and n-type silicon (Si) doped -GaN layers were
grown by metal-organic vapor phase epitaxy (MOVPE) on c-plane sapphire
(-Al2O3). The four-parameter semi-quantum
(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
-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
-Al2O3.© 1999-2000 The Materials Research Society