Ion Implantation - Mossbauer Spectroscopy - page 288

Fig. 6.23 Charge state dependent diffusivity of Fe in Si [ 38 ]

submission and approval of project proposals. In practice access for on-line 57 Mn
experiments is limited to one week per year, at both experimental facilities. The
authors of this tutorial are active at both sites.
The facilities are complementary in the energy of the 57 Mn beams provided.
While the radioactive 57 Mn beams at CERN are accelerated to about 50 keV, as in
the 57 Co off-line experiments discussed in Sect. 6.2 , and result in shallow
implantation depths of the order of 10 nm, the radioactive 57 Mn beams at RIKEN
are accelerated to several 100 MeV resulting in implantation depths of hundreds of
micrometers. As will be demonstrated in the Sect. 6.5 , this allows to study
materials deep below surface layers, as e.g. in electrode-covered solar cells.
Both on-line experimental facilities have been and are still involved in studies
on Fe in Si. In the framework of this tutorial we show one such example [ 38 ]. The
authors compared the Mössbauer spectra of 57 Fe in the decay of 57 Mn in two
silicon samples with very different doping levels, extremely p-type (p ++ ) and
highly n-type (n + ). They found that interstitial Fe atoms were created in silicon at
400-800 K as a result of the recoil imparted on these daughter atoms in the b-
decay of ion-implanted, substitutional 57 Mn. Then they observed that diffusional
jumps of the interstitial 57m Fe cause a line broadening in their Mössbauer spectra,
which is directly proportional to their diffusivity, as discussed in the preceding
chapter. Thus, the charge-state-dependent diffusivity has been determined in dif-
ferently doped material as shown in Fig. 6.23 [ 38 ].