A study of iron-related centers in heavily boron-doped silicon by deep-level transient spectroscopy

Deep levels in iron-diffused heavily boron-doped silicon are investigated by means of deep-level transient spectroscopy (DLTS). For interstitial iron Fe_i a donor state is observed at 0.39 eV above the top of the valence band E_v. It is proposed that Fe_i exhibits charge-dependent annealing characteristics, and in its neutral charge state Fe_i is mobile at temperatures as low as ≊280-230 K. Three other Fe-related donor states are observed at E_v+0.53 eV, E _v+0.60 eV, and ≊E_v+0.63 eV. The latter two states, not reported in any previous DLTS study, are produced in comparable concentrations to that of Fe_i upon annealing at 100 °C, whereas the former state present directly after quenching is suggested to result from a complex defect containing Fe_i. It is also argued that the level observed in this study at E_v+0.60 eV is the same as the one reported earlier at 0.55 eV below the bottom of the conduction band, but that it corresponds to a donor state of an Fe-related defect, in contrast to previous suggestions of it being an acceptor state. The annealing behavior of the defect states observed is studied up to 300 °C, and possible interactions involving Fe_i are discussed.