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Electronic Structure and Temperature Dependence of Excitons in GaN

Published online by Cambridge University Press:  15 February 2011

I. A. Buyanova ,
J. P. Bergman ,
W. Lil ,
B. Monemar ,
H. Amano  and
I. Akasaki
I. A. Buyanova
Affiliation:
Dept of Physics and Measurement Technology, Linköping University, S-581 83 Linkoping, Sweden, [email protected]
J. P. Bergman
Affiliation:
Dept of Physics and Measurement Technology, Linköping University, S-581 83 Linkoping, Sweden, [email protected]
W. Lil
Affiliation:
Dept of Physics and Measurement Technology, Linköping University, S-581 83 Linkoping, Sweden, [email protected]
B. Monemar
Affiliation:
Dept of Physics and Measurement Technology, Linköping University, S-581 83 Linkoping, Sweden, [email protected]
H. Amano
Affiliation:
Department of Electrical Engineering, Meijo University, Tempaku-ku, Nagoya 468, Japan
I. Akasaki
Affiliation:
Department of Electrical Engineering, Meijo University, Tempaku-ku, Nagoya 468, Japan
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Abstract

We present an optical study of the excitonic properties of epitaxial GaN using reflectivity and photoluminescence (PL) measurements. The values for the intrinsic exciton energies are found to be dependent on the built in strain developed due to the difference in thermal expansion coefficients between the GaN epilayer and the foreign substrate. For GaN on sapphire thecompressive biaxial strain causes an upshift of A and B excitons by typically 15 meV relative to the strain free sample, in accordance with previous data. For GaN on SiC, on the other hand, a downshift ˜ 8 meV in the free exciton energies is observed at 2K. Only two excitonic peaks about 18 meV apart, are resolved in reflectivity spectra for GaN on SiC, probably due to the overlapping of A and B excitons. The suggested explanation implies the reduction of the bandgap energy and of the valence band splitting under the action of a biaxial tensional strain in the GaN layer. For all structures the strain-induced shifts of the bandgap energy are much smaller at elevated temperatures, presumably reflecting the temperature dependence of the accumulated strain energy. The exciton-polariton structure of the GaN is also discussed. The enhanced intensity of the no-phonon (NP) A line compared to its longitudinal (LO) phonon replica is suggested to be partially attributed to strong defect scattering.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 423: Symposium E – III-Nitride, SiC, and Diamond Materials for Electronic , 1996 , 675
Copyright
Copyright © Materials Research Society 1996

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