Radiation hard detectors from silicon enriched with both oxygen and thermal donors: improvements in donor removal and long-term stability with regard to neutron irradiation

Abstract

Detectors made on the silicon wafers with high concentration of thermal donors (TD), which were introduced during the high temperature long time (HTLT) oxygenation procedure, have been investigated in the study of radiation hardness with regard to neutron irradiation and donor removal problems in irradiated high resistivity Si detectors. Two facts have been established as the evidence of radiation hardness improvement of HTLT(TD) Si detectors irradiated below ∼10 14 n/cm 2 compared to detectors made on standard silicon wafers: the increase of space charge sign inversion fluence (of 1 MeV neutrons) due to lower initial Si resistivity dominated by TD, and the gain in the reverse annealing time constant τ favourable for this material. Coupled with extremely high radiation tolerance to protons observed earlier (“beta zero” behaviour in a wide range of fluence), detectors from HTLT(TD) Si may be unique for application in the experiments with multiple radiations. The changes in the effective space charge density ( N eff) in as-irradiated detectors as a function of neutron fluence have been fitted using three different models. It has been shown that a new model with a universal donor removal rate for both materials, and considering the contribution of non-removable TD to the N eff provides good fit to the experimental data. A defect level related to TD has been observed in DLTS spectra of HTLT Si(TD) near T∼75 K. The physics of donor removal in irradiated silicon detectors is discussed.