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Disorder Induced IR Anomaly in Hexagonal AlGaN Short-Period Superlattices and Alloys

Published online by Cambridge University Press:  10 February 2011

A. M. Mintairov ,
A. S. Vlasov ,
J. L. Merz ,
D. Korakakis ,
T. D. Moustakas ,
A. O. Osinsky ,
R. Gaska  and
M. B. Smirnov
A. M. Mintairov
Affiliation:
EE Department, University of Notre Dame, Notre Dame, IN 46556
A. S. Vlasov
Affiliation:
EE Department, University of Notre Dame, Notre Dame, IN 46556
J. L. Merz
Affiliation:
EE Department, University of Notre Dame, Notre Dame, IN 46556
D. Korakakis
Affiliation:
ECE Department, University of Boston, Boston,MA, 02215
T. D. Moustakas
Affiliation:
ECE Department, University of Boston, Boston,MA, 02215
A. O. Osinsky
Affiliation:
APA Optics. 2950 N.E. 84th Lane, Blaine, MN, 55434
R. Gaska
Affiliation:
APA Optics. 2950 N.E. 84th Lane, Blaine, MN, 55434
M. B. Smirnov
Affiliation:
Institute for Silicate Chemistry, Odoevskogo 24/2, 199155 St.Petersburg, Russia
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Abstract

We report an experimental (infrared reflectance spectroscopy) and theoretical study of the polar optical phonons in hexagonal ternary nitride compounds: AlNm/GaNn (n=2-8, m=4, 8) superlattices (SL) and spontaneously ordered AlxGa1−xN (x=0.08–0.55) alloys. In infrared (IR) reflectivity spectra we revealed two modes having strong LO-TO splitting (20–150 cm−1), and several modes, having a small (1–3 cm−1) LO-TO splitting. All modes have a very high damping parameter ≥20 cm−1. The unusual observation is the negative value of the oscillator strength for the weak IR mode at ∼690 cm−1, suggesting possible lattice instability, consistent with high damping observed. We found from lattice dynamical calculations that weak IR active modes correspond to modes localized at GaN-AlN interfaces. Our analysis has shown that an anomalous mode is induced by the disorder effects and arises due to strong overlapping of the LO-TO phonon branches of the bulk GaN and AlN. In SL samples the anomalous mode corresponds to phonons localized on interface inhomogenities.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 572: Symposium Y – Wide-Bandgap Semiconductors for High-Power, High Frequency… , 1999 , 427
Copyright
Copyright © Materials Research Society 1999

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References

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