PICTS analysis of extended defects in heavily irradiated silicon

We report an experimental study on radiation-induced defects in silicon p⁺n junctions irradiated with 1 MeV neutrons up to a fluence of ≈2×10¹⁵ cm^-2. Heavily irradiated silicon diodes have been studied by means of Photon Induced Current Transient Spectroscopy (PICTS) technique using a variable filling time. A dominant broad and structured peak has been found in the temperature range 200-300 K. The behavior of this broad peak upon changing the filling time has been analyzed, and it is observed that spectral line-shape broadens toward lower temperature as the filling time is increased. The observed spectra shape modification cannot be explained only in terms of isolated point defects being consistent with quasicontinuous distributions of deep levels inside the bandgap. We suggest that the investigated broad peak is, at least in part, generated by emission from defect clusters.