Detection of Substitutional and Interstitial Fe in Silicon by Mössbauer Spectrocopy

Abstract

A novel approach to create radioactive, substitutional and interstitial 57Fe atoms in silicon at elevated temperatures is reported, which allows for Mössbauer studies of the emitted 14 keV γ-radiation. Radioactive 57Mn + (T1/2 = 1.5 min) ions have been implanted at the ISOLDE facility at CERN with 60 keV energy to fluences <1012/cm2 into silicon crystals held at 400–800 K. As a result of the annealing of the radiation damage during the 57Mn lifetime, the Mn atoms are found on substitutional lattice sites. In the subsequent decay of 57Mn to the Mössbauer state of 57Fe an average recoil energy of 40 eV is imparted on the daughter atom. This leads to a relocation into interstitial sites for the majority of the Fe atoms, the remainder remains on substitutional sites. Thus the Fe electronic and vibrational properties on both lattice sites can be studied. A few diffusional jumps of interstitial Fe during the lifetime of the Mössbauer state (T1/2 = 100 ns) have been observed by a broadening of their Mössbauer line at >450 K. At the highest temperatures a new line occurs in the spectra, the possible nature of this line will be discussed.