Neutral interstitial iron center in silicon studied by Zeeman spectroscopy

Abstract

The Zeeman effect of the interstitial iron defect in silicon has been investigated by high-resolution Fourier-transform spectroscopy. Two sets of experimentally observed line spectra have previously been identified as optical excitations of neutral interstitial iron, ${\mathrm{Fe}}_{i}^{0}.$ The first set arises when an electron is excited to a shallow-donor-like state, ${\mathrm{Fe}}_{i}^{0}+h\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\nu}}{\mathrm{Fe}}^{+}{+e}^{\ensuremath{-}},$ where the electron is decoupled from the ${\mathrm{Fe}}^{+}$ core whose ground state is a ${}^{4}{T}_{1}$ term. The second set arises when an excited electron of ${a}_{1}$ symmetry is coupled by exchange interaction to the ${\mathrm{Fe}}^{+}$ core, yielding a ${}^{5}{T}_{1}$ final state. The Zeeman behavior of these transitions is studied in order to verify the assignment of the states and the effective-mass-like character of the decoupled electron. Detailed information on the initial state and on the properties of the iron core is gained. Experiments determine the multiplet splitting of the ${}^{4}{T}_{1}$ and ${}^{5}{T}_{1}$ states due to spin-orbit interaction but large deviations from the Land\'e interval rule are observed, as well as a marked decrease in intensity for the high-energy components. Our analysis confirms that the ${}^{4}{T}_{1}$ and ${}^{5}{T}_{1}$ states are closely related, and a dynamical Jahn-Teller distortion is suggested to be the dominant mechanism responsible for the non-Land\'e behavior.