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Profiling Composition Variations in Composition-Modulated GaP/InP Short-Period Superlattices Using Resonance Raman Scattering

Published online by Cambridge University Press:  10 February 2011

H. M. Cheong ,
Yong Zhang ,
A. G. Norman ,
J. D. Perkins ,
A. Mascarenhas ,
K. Y. Cheng  and
K. C. Hsieh
H. M. Cheong
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401
Yong Zhang
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401
A. G. Norman
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401
J. D. Perkins
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401
A. Mascarenhas
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401
K. Y. Cheng
Affiliation:
Dept. of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois 61801
K. C. Hsieh
Affiliation:
Dept. of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois 61801
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Abstract

We use resonance Raman scattering (RRS) and electroreflection (ER) measurements to profile the the composition and strain variations in laterally composition-modulated (CM) GaP/InP short-period superlattices (SPS's). The ER spectra of a GaP2.2/InP2.0 SPS give the fundamental band-gap energy at 1.69±0.05eV, which is about 210 meV lower than the band gap energy of a GaInP random alloy with the same overall composition. The RRS measurements reveal strong dependences of the phonon spectrum on the polarization and the excitation energy. In RRS spectra measured with the polarization of both excitation and scattered photons along the composition modulation direction, the GaP-like longitudinal optical (LO) phonon redshifts by 4.0±0.5 cm−1 near the resonance with the fundamental energy gap. On the other hand, when the polarizations are orthogonal to the composition modulation, the LO phonons redshift as much as 16 cm−1 at low excitation energies. A comparison of the experimental data with a model calculation gives the average In composition in the In-rich region as 0.70±0.02, and the average Ga composition in the Ga-rich region as 0.68±0.02. Our result also indicates that there are small volumes (less than 1% volume fraction) with very high In mole fraction.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 583 , 1999 , 361
Copyright
Copyright © Materials Research Society 2000

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Footnotes

†

Present Address: Dept. of Physics, Sogang University, Seoul, Korea

References

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