Characterization of radiation-related damage in bulk-grown silicon-germanium detectors

Electrical properties of irradiated p-type, PIN, Si_1-xGe_x ( x = 0.028) devices were compared to the similar non-irradiated devices, which were fabricated on the same wafer. Differences in effective doping concentration, current generation mechanisms and the process activation energies were observed. Effective doping decrease with increasing irradiation fluence was attributed to the acceptor removal process. Material resistivity was measured, for both irradiated and non-irradiated samples, showing radiation-induced increase in material resistivity, which correlated with the acceptor removal hypothesis. Changes in current generation mechanism were attributed to the radiation-induced generation-recombination centers creation. Dominance of the Space Charge Region (SCR) current generation mechanism was assumed and confirmed for both irradiated and non-irradiated devices. The activation energy of the generation process was shown to be near the theoretical mid-gap. Deep level traps were examined using a current Deep Level Transient Spectroscopy (DLTS) technique. A trap level, with activation energy of 0.43 eV, was detected in both irradiated and non-irradiated samples. The irradiated samples exhibited two additional trap levels with activation energies of 0.12 and 0.27 eV, the levels were attributed to corresponding dislocation types. The 0.12 eV level attribution to B_I^{0 / +} trap correlated with the radiation-induced boron removal hypothesis.