9 Mössbauer Spectroscopic Studies on Atomic Diffusion in Materials
483
Furthermore, we have developed a mapping technique, which we will describe later,
to study
57 Fe diffusion and segregation in Si materials [83–90]. These studies have
clarified the solid solution of Fe impurities in Si [91–93]: The Fe impurities occupy
not only interstitial sites but also substitutional sites. Besides, the carrier trapping
cross sections for the interstitial components with different charge states, Fe i
+ and
Fe i
2+ , can be successfully obtained by evaluating the dynamical charge fluctuations
within a time scale of 100 ns between Fe i
+ and Fe i
2+ which were observed directly
in the Mössbauer spectra of
57 Fe doped mc-Si solar cells [82].
After GeV57 Mn/
57 Fe implantation into Si wafers, we found
57m Fe atoms to
occupy interstitial and substitutional sites [72–77]. The results appear to coincide
those obtained at CERN ISOLDE using low energy implantation of
57 Mn into Si
[93]. We use the assignments based on the isomer shift values, which relate to the
charge density at the
57 Fe nucleus. We refer the first-principle theoretical calculations
[94, 95], but there remains still discrepancies when we discuss the charge states of
interstitial Fe in Si materials. Figure 9.37(a) shows Mössbauer spectra of
57 Fe in
n-type FZ-Si in the temperature region between 330 and 1200 K [77]. The spectra
from 330 to 700 K can be fitted by two Lorentzian singlets, while those from 800 K
up to 1200 K can be analyzed only by a broad singlet. We assigned the two singlets
at 330 K at the left, and the right-hand side has been to Fe int
+ and Fe sub
0 atoms on
interstitial and substitutional sites in the Si matrix, respectively. The spectra change
(a)
(b)
Fig. 9.37 (a) Mössbauer spectra of 57 Fe in n-type FZ-Si measured between 330 and 1200 K.
Notice that the vertical scale for the region above 900 K is blown up with a factor of two, in order
to show the small and broad resonance effects more clearly. (b) The model reproduces the overall
temperature dependence of the Mössbauer spectra of 57 Fe in n-type FZ-Si measured between 330
and 1000 K. (From Ref. [77])
483
Furthermore, we have developed a mapping technique, which we will describe later,
to study
57 Fe diffusion and segregation in Si materials [83–90]. These studies have
clarified the solid solution of Fe impurities in Si [91–93]: The Fe impurities occupy
not only interstitial sites but also substitutional sites. Besides, the carrier trapping
cross sections for the interstitial components with different charge states, Fe i
+ and
Fe i
2+ , can be successfully obtained by evaluating the dynamical charge fluctuations
within a time scale of 100 ns between Fe i
+ and Fe i
2+ which were observed directly
in the Mössbauer spectra of
57 Fe doped mc-Si solar cells [82].
After GeV57 Mn/
57 Fe implantation into Si wafers, we found
57m Fe atoms to
occupy interstitial and substitutional sites [72–77]. The results appear to coincide
those obtained at CERN ISOLDE using low energy implantation of
57 Mn into Si
[93]. We use the assignments based on the isomer shift values, which relate to the
charge density at the
57 Fe nucleus. We refer the first-principle theoretical calculations
[94, 95], but there remains still discrepancies when we discuss the charge states of
interstitial Fe in Si materials. Figure 9.37(a) shows Mössbauer spectra of
57 Fe in
n-type FZ-Si in the temperature region between 330 and 1200 K [77]. The spectra
from 330 to 700 K can be fitted by two Lorentzian singlets, while those from 800 K
up to 1200 K can be analyzed only by a broad singlet. We assigned the two singlets
at 330 K at the left, and the right-hand side has been to Fe int
+ and Fe sub
0 atoms on
interstitial and substitutional sites in the Si matrix, respectively. The spectra change
(a)
(b)
Fig. 9.37 (a) Mössbauer spectra of 57 Fe in n-type FZ-Si measured between 330 and 1200 K.
Notice that the vertical scale for the region above 900 K is blown up with a factor of two, in order
to show the small and broad resonance effects more clearly. (b) The model reproduces the overall
temperature dependence of the Mössbauer spectra of 57 Fe in n-type FZ-Si measured between 330
and 1000 K. (From Ref. [77])