Defect reactions occurring in Ge:Bi, O crystals during electron and γ irradiation at room temperature, and following isochronal annealing at 80 to 350C, were studied by means of deep-level transient spectroscopy and high-resolution Laplace deep level transient spectroscopy. It was shown that Bi and O impurity atoms were the most effective traps for mobile vacancies created in the crystals by irradiation. Both the vacancy–oxygen (A center) and vacancy–Bi (Bi–V or E center) defects in Ge had three charge states and introduce two energy levels into the gap. The ratio of concentrations of the VO and Bi–V centres in as-irradiated samples depends on the relative concentrations of interstitial oxygen (Oi) and substitutional bismuth (Bis) atoms. Annealing studies demonstrated that, at 120 to 150C, the concentration of the Bi–V center increases. This was associated with the dissociation of VO that occurred in the range of 100 to 150C. In consequence the proposed mechanism was the release of vacancies from the A center which were subsequently trapped by the Bi impurity atoms to form the Bi–V E center. It was suggested that the enhanced disappearance of the Bi–V centres in electron-irradiated oxygen-rich Ge samples was associated with the interaction of the E centres with mobile Ge self-interstitials released from oxygen-related traps at above 140C.

Vacancy Defect Reactions Associated with Oxygen and Bismuth in Irradiated Germanium. V.P.Markevich, A.R.Peaker, V.V.Emtsev, V.V.Litvinov, L.I.Murin: Physica B, 2006, 376-377, 93-6