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Submitted on 1 Jan 1981
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PHONON-LINE-SHAPE AND DISORDER CORRELATION IN MIXED GaP1-xAsx
M. Teicher, D. Schmeltzer, R. Beserman
To cite this version:
M. Teicher, D. Schmeltzer, R. Beserman. PHONON-LINE-SHAPE AND DISORDER CORRE- LATION IN MIXED GaP1-xAsx. Journal de Physique Colloques, 1981, 42 (C6), pp.C6-46-C6-48.
�10.1051/jphyscol:1981613�. �jpa-00221193�
JOURNAL DE PHYSIQUE
CoZZoque C6, suppZ6ment au nO1 2, Tome 42, d6cembre 1981 page C6-46
PHONON-LINE-SHAPE AND DISORDER CORRELATION IN MIXED Gap1-,As,
M. Teicher, D. Schmeltzer and R. Beserman
Solid S t a t e I n s t i t u t e and physics Dept., Teehnion, Haifa, IsraeZ
Abstract. - The disorder of Gap As is evaluated from the double phonon 1-x x
spectrum and compared to the amorphous material.
Combinations between zone edge Raman active phonons are used to define the disorder in a mixed crystal. These phonons have large "q" and therefore are sensitive to spatial disorder. The change in line width and shape of the double phonon spectrum of mixed Gap As is compared to the amorphous Raman width of the
1-x x pure components.
GaPl-xA~x has a two-mode-zone center and zone-edge behaviour. The second order spectrum of Gap As is composed of combinations of zone edge phonons of Gap alone
1-x x
and GaAs alone. Figure 1 shows the spectra of the Gap optical double phonons as a function of As content. With increasing "x" the spectrum is shifted and broadened, we shall focuss our attention on this broadening. The same results are obtained for the GaAs double phonon spectrum.
The normalized Raman spectrum I(@) is related to the phonon density of states g(@ by:
6 W
g(w) is the double phonon Raman spectrum at half width. By fitting procedure,
Chis taken as a phenomenological width. Figure 2 compares the double-phonon 6
spectum of Gap to the amorphous spectrum, the spectrum agrees well with the amorphous one.
If we make the hypothesis that the disorder which is introduced by mixing Gap with GaAs, is of the same nature than the disorder created by amorphisation, a correlation should exist between the widths of the GaPl-xA~x spectrum and that of amorphous Gap.
On figure 3, we plot the Gap double phonon width as a function of As concentration this curve extrapolates to the width of the amorphous material. This result can best be understood by assuming that GaP(GaAs) agregates into microcrystallite clusters, the other component prevents the propagation of the GaP(GaAs) phonon from cluster to
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981613
cluster . This results in the alternation and in the broadening of the propagating vibrational mode. When the concentration of Gap (GaAs) is small enough, the clusters are isolated one from the other,the barrier between them is to high to be overcomed, this is the picture of an amorphous material.
WAVE NUMBER ( C I I I - I )
Fig. 1:- Gap double-phonon Raman spectra for different As concentrations in GaP1-xA~x.
JOURNAL DE PHYSIQUE
AMORPHOUS SPECTRUM
m
,
6 0 0 650 700 750 8 0 0 850
WAVE NUMBER (Cm-1)
Fig. 2:- Broadened double-phonon Gap spectrum, compared to the amorphous spectrum of Gap.
Fig. 3:- Gap double-phonon line-width, as a function of As concentration in mixed GaPl-xAsx.
