Chemistry Reference
In-Depth Information
Fig. 6.11
57
Fe spectra after
ion implantation of
57
Co at
50 K and after subsequent
annealing [
25
]
high fluence implantation experiments, as well as in Fe
x
Si
1-x
films for low x values,
and appears to contribute also to the spectra at low fluence. This defect configuration
is therefore often called the ''amorphous site'' and thought to be representative of the
amorphized region generated by the collision cascade of single implanted ions.
A substitutional configuration was suggested for a third site (d =
-0.07(3) mm/s) on the basis of the Fe
i
? V ? Fe
s
model and from theoretical
calculations. This configuration is attributed to Fe atoms that find themselves
outside the amorphized collision cascade region, or in a recrystallized part of it.
Upon annealing low fluence implanted
57
Co/
57
Fe a surprising observation was
made. A new spectrum component appeared (Fig.
6.14
) with extra Mössbauer
resonances at both sides of the spectrum components discussed so far.
It would lead us so far to discuss in detail the dependence of this spectrum
component on annealing temperature, fluence and substrate doping. Based on these
dependencies, it has been assigned to Co
2
pairs in Si [
27
].
Also other pairs were recognized, formed by normal acceptors in Si and Co
donor atoms (CoB, CoAl, CoGa, CoIn) [
28
]. The different Fe and Co silicides have
been characterized in several experimental studies and are observed as small
precipitates after diffusion experiments and also in larger (often epitaxial) struc-
tures in ion beam mixing experiments, or in experiments to form buried epitaxial
layers. A discussion on studies on these larger configurations around Fe in Si is
beyond the scope of this tutorial.
We will also not discuss other Mössbauer probes in semiconductors, e.g. the
5sp-elements
119
Sn,
121
Sb,
125
Te and
129
I. They were used with success to probe
