Defects in electron-irradiated Ge studied by positron lifetime spectroscopy

The formation and annealing behavior of electron-irradiation induced defects in germanium were studied. The undoped Ge samples were irradiated at 4 K with an electron energy of 2 MeV. The fluence was varied between ${10}^{15}$ and ${10}^{19}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}.$ Annealing experiments were performed from 90 K. Additional temperature-dependent positron lifetime measurements after different annealing stages were carried out to make a statement about charge states of defects and to the presence of shallow positron traps. Two main annealing stages were observed. The first between 150 and 250 K was attributed to the annealing of Frenkel pairs. The second annealing stage between 350 and 450 K was observed after irradiation with fluences above ${10}^{17}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ and was assigned to annealing of a complex containing a vacancy and an impurity atom. Furthermore, shallow positron traps were detected after irradiation. This defect type anneals above 330 K in a wide-temperature range.

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