Investigation on the long-term radiation hardness of low and medium resistivity starting silicon materials for RT silicon detectors in high energy physics

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Relatively low and medium resistivity (200 to 2000 Ω cm) starting silicon materials have been studied in the search of room temperature neutron radiation-hard silicon detectors. It has been found that moderate resistivity (300–700 Ω cm) silicon detectors, after being irradiated from 5.0 × 1013 to 2.0 × 1014 n/cm2, are extremely stable in terms of the detector full depletion voltage (Vd) or the net effective concentration of ionized space charges (Neff) - there is little “reverse annealing” of Neff at RT and elevated temperatures, as compared with large reverse annealing observed for high resistivity silicon detectors. Detectors with starting resistivity of 300–700 Ω cm have been found to be stable, during the equivalent of one year RT anneal that would reach the saturation of the first stage of reverse anneal, within the Neff window of |Neff| ≤ 2.5 × 1012 cm−3 (Vd = 180 V for d = 300 μm) in a working range of 5.0 × 1013 to 1.5 × 1014 n/cm2, or a net neutron radiation tolerance of 1.0 × 1014 n/cm2. The observed effects are in very good agreement with an early proposed model, which predicted among others, that there might be an off-set between the reverse annealing effect (increase of net acceptor-like ionized states in the space charge region with time) and the partial annealing of the PV centers that leads to the partial recovery of the shallow impurity donors (phosphorus in this case). Study on detectors with various starting resistivities has indicated an optima starting resistivity of about 1.6 kΩ cm for which the detector full depletion voltage is under 180 V for a 280 μm thick detector before and after neutron radiation and after reverse anneal.