Influence of deep levels on space charge density at different temperatures in γ-irradiated silicon

In this work, it is shown that the analysis of thermally stimulated currents (TSC) and current transients (CT) at constant temperature can be a suitable tool to study the influence of deep levels on space charge density N(T) in irradiated silicon diodes. In particular, the occurrence of space charge sign inversion (SCSI) can be related to signal discontinuities in TSC and CT measurements. This approach has been adopted in this work to study devices made of standard Float Zone (FZ) and Diffusion Oxygenated Float Zone silicon, irradiated by γ-rays up to a dose of 300 Mrad. Our study shows that all the samples are inverted at 50 K after a low-temperature excitation. Several space charge sign inversions, from positive to negative and vice versa, have been observed between cryogenic and room temperature, and have been related to carriers emission from dominating deep traps. Only standard FZ silicon remains inverted at room temperature after a dose of 300 Mrad.