Spin-dependent recombination electron paramagnetic resonance spectroscopy of defects in irradiated silicon detectors

Spin-dependent recombination (SDR) electron paramagnetic resonance (EPR) spectroscopy is applied for investigation of paramagnetic recombination centers in irradiated silicon p-n junction detectors (diodes) formed on float-zone (FZ) silicon wafers. The main radiation defects, associated with SRD-EPR spectra arising from excited triplet states, are assigned to complexes of two substitutional carbon atoms and one interstitial silicon atom (CS+SiI+CS) and to oxygen + vacancy (O+V) complexes (A-centers). In spite of the low concentration of oxygen in FZ silicon the A-centers are found to play an important role in the recombination process in the diodes. At temperatures T<100 K the SDR-EPR spectra are well observable by measurements of the microwave conductivity or by detecting a dc forward current IF below a forward-blocking voltage UFBL. At UFBL the IF has a steep jump followed by a decrease of the voltage over the diode and a negative resistance region with oscillations of the current. The SDR-EPR spectrum arising from the (CS+SiI+CS) complexes was found to decrease strongly in the forward biased diodes. This effect can be attributed to coexistence of two different configurations of the carbon related defect in the bulk n-type region of the diodes