In situ observation of substitutional and interstitial Fe atoms in Si after GeV-implantation: An in-beam Mössbauer study

Unstable isotopes of ⁵⁷Mn (τ1/2=1.45m) are separated and implanted into FZ- and CZ-Si wafers using a RIKEN projectile nuclear fragment separator (RIPS). Subsequently, Mössbauer spectra of ⁵⁷Fe in Si are measured at high temperatures up to 800 K, in order to study the charge states and the diffusion processes of interstitial and substitutional Fe atoms in Si matrix. The spectra consist of two singlets between 300 and 650 K, and only one singlet above 700 K. The isomer shifts of the singlets at 300 K are 0.809(13) and -0.042(38) mm/s, referring to the value of α-Fe. The values correspond to interstitial and substitutional Fe, respectively. Above 600 K, both the disappearance of the interstitial component and the simultaneous relaxation effects on the centre shifts are clearly observed. These dynamical behaviours can be interpreted as a reaction process of interstitial Fe atoms jumping into vacancies, which are accompanied by changes in the charge states. Above 650 K a line broadening of the singlet can be also seen, indicating an enhanced diffusion of the Fe atoms due to the excess vacancies.