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ON THE LOCALIZATION OF Co ATOMS IN SILICON
I. Dézsi, R. Coussement, G. Langouche, B. Molnar, D. Nagy, M. de Potter
To cite this version:
I. Dézsi, R. Coussement, G. Langouche, B. Molnar, D. Nagy, et al.. ON THE LOCALIZATION OF Co ATOMS IN SILICON. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-425-C1-426.
�10.1051/jphyscol:19801165�. �jpa-00219652�
JOURNAL DE PHYSIQUE Colloque C l , suppldment au n O 1 , Tome 41, janvier 1980, page C1-425
ON ME LOCALIZATION OF Co ATOF.1S IN SILICON
I. DBzsi, R. Coussement W
,
G. ~ a n ~ w c h e * , B. Molnar, D.L. Nagy and M. de potter*Central Research I n s t i t u t e for Physics, H-1525 Budapest, Hungary.
x I n s t i t u u t voor Kern- en Stralingsfysika, University of Leuven, B-3030, Leuven, Belgium.
Numerous studies have been made in order to lo-
-
Incalize the Co impurity atoms in the silicon lattice
*
C /I 1-181. First, Norem and Wertheim / 1 / suggested 3 for Co diffused silicon samples that their MGSS-
f
bauer spectrum could be analysed in terms of sub-
- .- 2
stitutionally and interstitially located Co atoms.
e
Other authors offered different explanations, e.g.
-
0segregated Co metallic clusters. We performed
>
Mijssbauer studies on various Co intermetallic com-
k
y)pounds of Si doped with 5 7 ~ o , and on 5 7 ~ o implan- Z
W ted Si samples subsequently annealed at 1000' C. I- Our aim was to get information whether the inter-
z
metallic phases do appear in diffused C o g and an- nealed 57~oSi implanted samples. .
CoSi, CoSi2, CoSi3 intermetallic compounds were prepared by using the method described in ref 191.
The samples were annealed at 900" C to ensure the maximum phase homogeneity. 5 7 ~ o activity was dif- fused into the lattices in hydrogen atmosphere and in vacuo, but no difference in the spectra could be observed by using either hydrogen or vacuum. A single line absorber of K4[Fe(CN)6]
.
3H20 with0.2 mg/cm2 5 7 ~ e was used. The 6 values are given relative to metallic iron.
The ~Essbauer spectra are shown in Fig. 1 and 2. All spectra measured are very similar except CoSi. The shape of the spectrum of the latter com- pound was found to be the same as it was published in ref. /lo/. The isomer shift (6) and quadrupole splitting (AE) values are -0.33 (I) mm/s and 0.17 (2) mm/s respectively. These values are very near towhat was found in ref. /lo/ (6 = -0.29 mm/s, AE = 0.20 mm/s). The spectra of CoSi2 and CoSi 3 are very similar to each other in H = 0 and in H = 80 kOe (H /Iy) as well. The spectra in H = 0 could be fitted by assuming two single lines and also with one single line + a quadrupole doublet.
The values obtained : g l = -0.48 (2) mm/s, 6 =
2
-
2 - 1 0 1 20.02 (I) mm/s with two single lines and 6 =
Q VELOCITY lmm/sec)
-0.30 (1) mm/s, 6S = 0.03 (2) and AE=0.40 (2) mm/s with one singlet and one doublet. The spectra
measured in H = 80 kOe external field could be fit- Figure 1 : Measurements i n zero external f i e l d .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801165
C 1-426 JOURNAL DE PHYSIQUE
Figure 2 : Measurements in 80 kOe external field.
ted well by two magnetically split spectra with A E = 0. The fit gave H I = 70 kG and Hz = 75 kG values. These values are less than that of the applied field probably becauseof a small magnetic moment on the Fe atoms in these lattices similarly as it was found in CoSi /lo/. The fit with AE # 0 would result in a larger (%I5 kG) difference in H
1 an Hz. The structure of CoSi2 is cubic of type CI /I
11.
Therefore, no electric field gradient is ex- pected for substitutional Co sites. We attribute the line with 6 =0.02 mm/s to this site (relative2
intensity is 70 %). The origin of the line with6 =
1 -0.48m/s cannot be known for sure. It would be tempting to assign this line to CoSi existing as an impurity phase in CoSi2 and CoSi3 but an X-ray dif- fraction study did not support this idea. Further- more, the spectra in H = 80 kOe could not be fitted well with the 6 and H values found for CoSi + a Zee- man split spectrum with BE = 0. Tfierefore we be-
lieve this line belongs to a site of high point sym- metry. The structure of CoSig has not been deter- mined yet up to our notice, but because of the si- milar spectrum obtained suggest that the structure
around the Co atoms is similar as it is in CoSi 2 ' The spectra of Co diffused in Si and Co implan- ted in Si and subsequently annealed at 1000° C are very similar to the spectra of CoSi and CoSi3. The
2
values at H = 0 are the same but in H # 0 the spec- tra are only qualitatively similar. In the latter case this is not surprising if we attribute the spectra to Co sites in segregated clusters where the sizes of clusters could bear the responsibili- ty for these small discrepancies. Also it has to be noted that contrary to ref. /7/ no any other lines appeare in the spectra which could be attri- buted to Fe in metallic clusters.
In summary, we conclude that the Co atoms dif- fused in Si and implanted in Si and subsequently annealed form segregated intermetallic phases with Si, similarly to Fe implanted and subsequently annealed Si samples 1131-1141.
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