Free-carrier effects and optical phonons in GaNAs/GaAs superlattice heterostructures measured by infrared spectroscopic ellipsometry
J. Sik
Center for Microelectronic and Optical Materials Research and Department of Electrical Engineering, University of Nebraska-Lincoln
and
Department of Solid State Physics and Laboratory of Thin FIlms and Nanostructures, Faculty of Science, Masaryk University Brno
M. Schubert
Center for Microelectronic and Optical Materials Research and Department of Electrical Engineering, University of Nebraska-Lincoln
and
Fakultaet fuer Physik und Geowissenschaften, Arbeitsgruppe Halbleiterphysik,University Leipzig
T. Hofmann
Fakultaet fuer Physik und Geowissenschaften, Arbeitsgruppe Halbleiterphysik,University Leipzig
V. Gottschalch
Fakultaet fuer Chemie und Mineralogie, University Leipzig
This article was received on Thursday, March 2, 2000 and
accepted on Friday, April 21, 2000. Abstract
The
infrared-optical properties of
GaAs/GaNxAs1-x superlattice (SL)
heterostructures (0 < x < 3.3%) are studied by variable angle-of-incidence infrared spectroscopic ellipsometry (IRSE) for wavenumbers
from 250 cm-1 to 700 cm-1. The undoped SL structures
where grown on top of a 300 nm thick undoped GaAs buffer layer on Te-doped
(001) GaAs substrates by metal-organic vapor phase epitaxy (MOVPE). We observe
the well-known Berreman-polariton effect within the GaAs LO-phonon region. We
further observe a strong polariton-like resonance near the coupled
longitudinal-optical plasmon-phonon frequency of the Te-doped substrate at 306
cm-1. For analysis of the IRSE data we employ the harmonic
oscillator dielectric function model and the Drude model for free-carrier
response. The additional resonance feature is explained by pseudo surface
polariton (PSP) interface modes between the Te-doped GaAs and the undoped GaAs
buffer layer / SL film. We find that the PSP modes are extremely sensitive to
free-carrier properties within the SL structures, and we obtain a strong
increase in free-carrier concentration within the GaNAs SL sublayers with
increasing x from analysis of the IRSE data. We further observe the
localized vibrational modes of nitrogen at 470 cm-1 in the
GaNxAs1-x SL sublayers with a polar
strength that increases linearly with x, and which can be used to
monitor the nitrogen concentration in
GaNxAs1-x.Outline
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Cite this article as: MRS Internet J. Nitride Semicond. Res. 5, 3(2000).
last updated Friday, April 21, 2000 2:53:58 AM.© 2000 The Materials Research Society
