Moessbauer study of Sn impurity defect structures in GaAs

Radioactive 119Snsup(m) has been implanted in GaAs single crystals at room temperature with an energy of 60 keV. The creation and annealing of impurity-defect structures has been studied by means of Moessbauer spectroscopy on the 24 keV γ-transition of 119Sn. The distribution of defects surrounding the Sn impurity atoms in the amorphous phase has been characterised by an analysis of the measured Moessbauer spectra in terms of four lines. The formation and annealing of impurity-defect structures during the recrystallisation of the host crystal between about 200 to 4000C has been followed by Moessbauer spectroscopy. Between 250 to 3500C the fraction of Sn atoms on undisturbed substitutional lattice sites (supposedly Ga sites) is found to increase drastically. Three other defect structures have been distinguished in the Moessbauer spectra by different isomer shifts and Debye-Waller factors of the impurity atoms. One of these is assigned to an interstitial defect, the two others to vacancy complexes. Possible configurations of the defects are discussed on the basis of the Moessbauer parameters. The fractions of impurity atoms contained in the defect structures are found to depend on the implanted dose (1014 to 1016 atoms cm-2). Post implantation of hydrogen atoms seems to lead to the formation of a new defect structure which is tentatively assigned to the trapping of hydrogen in a Sn-vacancy structure. (author)