2001 Volume 70 Issue 9 Pages 2598-2602
We have investigated coherent longitudinal optical (LO) phonons in GaSb/AlSb superlattices. The coherent AlSb-like LO phonon in the barrier layer and the coherent GaSb-like LO phonon in the well layer have been simultaneously observed. The GaSb-like LO phonon exhibits a cosine-type oscillation, which is the dominant signal. We have analyzed the initial phase of the AlSb-like LO phonon by plotting the imaginary part of the Fourier-transform components as a function of the real part, the so-called Cole-Cole's plot. We have found from this plot that the difference in the initial phase between the GaSb-like and AlSb-like LO phonons is about 90 degrees: The AlSb-like LO phonon has a sine-type oscillation. This difference in the initial phase indicates the difference in the generation mechanism between the coherent GaSb-like and AlSb-like LO phonons. We discuss the generation mechanism based on some proposed models.
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