PICTS analysis of extended defects in heavily irradiated silicon

We report the results of an experimental study on radiation-induced defects in silicon p⁺n diodes irradiated with 1-MeV neutrons up to a fluence of 2.3 × 10¹⁵ cm^-2. Heavily irradiated silicon diodes have been studied by means of photo induced current transient spectroscopy (PICTS) technique using a variable filling time. For every filling time, a dominant broad and structured peak has been found in the temperature range 200-300 K. Such a broad peak cannot be accounted for by considering isolated point defects, being consistent with a quasi-continuous distribution of deep levels inside the bandgap. In addition, it is observed that the spectral lineshape tends to broaden as the filling time is increased. The details of the lineshape modifications depend strongly on the irradiation fluence of the sample, in such a way that they cannot be explained only in terms of emissions from noninteracting electron states. Thus we suggest that the investigated broad peak should, at least in part, be generated by emission from extended defects, also known as clusters.