Local vibrational mode spectroscopy of dimer and other oxygen-related defects in irradiated and thermally annealed germanium

Oxygen doped Ge has been irradiated with 2-MeV electrons and isochronally annealed between 80 and 440^∘C. In total 64 local vibrational mode bands from oxygen-related defects have been observed in the infrared absorption spectrum, 23 of the bands belonging to thermal donors. Two bands at 621.6 and 669.1cm^-1 (5 K) are assigned to respectively VO⁰ and VO^-, implying that the stretching mode of the A center in Ge is charge state dependent, similarly to the A center in Si. Bands at 525.5, 780.3, and 817.9cm^-1 (5 K) are assigned to three modes of the oxygen dimer. The wave-number positions are in excellent agreement with corresponding modes in Si and with published ab initio calculations for the dimer in Ge. The irradiation results in an enhanced formation of dimers and thermal donors. The annealing data of the dimer and the early thermal donor bands, support the model of the dimer being the first step in the oxygen agglomeration sequence of thermal donor formation. Preliminary results are also obtained concerning Ge-isotope splitting of some of the absorption bands.