Shallow defect levels in float-zone and diffusion oxygenated float-zone Si, before and after irradiation with a 60Co γ-source up to 300Mrad, were studied by thermally stimulated currents and deep-level transient spectroscopy at 4.2 to 110K. Besides vacancy oxygen (VO) and interstitial-substitutional carbon (CiCs) emissions, several thermally stimulated current peaks were observed. A trap with an activation energy of 11meV was observed at 6K only in irradiated diffusion oxygenated float-zone Si. Two hole traps, at 80 and 95meV, were observed both in irradiated float-zone and diffusion oxygenated float-zone Si, while a trap at 100meV, related to an interstitial-oxygen complex, was revealed only in irradiated diffusion oxygenated float-zone Si. A thermally stimulated current peak close to 24K was resolved into two components, whose concentrations were independent of irradiation fluence: a trap at 55meV and a level which remained charged after emission at 80meV. The measurements confirmed the formation, only in diffusion

oxygenated float-zone Si, of a radiation induced donor at 230meV. It appears to be responsible for the improved radiation hardness of oxygenated Si together with the suppression of deep acceptors, since no shallower radiation-induced donors were detected in diffusion oxygenated float-zone Si samples.

Shallow Energy Levels Induced by γ-Rays in Standard and Oxygenated Floating Zone Silicon. D.Menichelli, M.Scaringella, S.Miglio, M.Bruzzi, I.Pintilie, E.Fretwurst: Applied Physics A, 2006, 84[4], 449-53