Speaker
Zheng Li
(BNL)
Description
For the development of radiation-hard Si detectors for the SiD BeamCal program for International Linear Collider (ILC), n-type Magnetic Czochralski Si detectors have been irradiated first by fast neutrons to fluences of 1.5x1014 and 3x1014 neq/cm2, and then by gamma up to 500 Mrad. The motivation of this mixed radiation project is to develop a radiation-hard Si detector that can utilize the gamma/electron radiation to compensate the negative effects caused by neutron irradiation, all of which exists in the ICL radiation environment. By using the positive space charge created by gamma radiation in MCZ Si detectors, one can cancel the negative space charge created by neutrons, thus reducing the overall/net space charge density and therefore the full depletion voltage of the detector. It has been found that gamma radiation has suppressed the room temperature reverse annealing in neutron-irradiated detectors during the 5.5 month of time needed for the 500 Mrad radiation dose. The reverse annealing in control detectors (detectors having the same neutron fluences, but going through this 5.5 month room temperature annealing (RTA) without gamma radiation) was clearly taking place. This suppression is in agreement with our previous predictions, since negative space charge is generated during the reverse annealing, any suppression of that would mean creation of positive space charge by gamma radiation. The impressive effect is that regardless of the fluence the reverse annealing is totally suppressed by the same dose of gamma (500 Mrad): the full depletion voltage for the two detectors irradiated to two very different fluences stay the same before and after gamma radiation. Meanwhile, for the control detectors, the full depletion voltages have gone up in amounts proportional to the neutron fluence. This would imply that concentrations of positive space charge created in these two samples are different at the same gamma dose, and gamma irradiation effectively “switched off”, or “freeze” the RT reverse annealing of neutron irradiation. It has also been found that as soon as the gamma irradiation stops, the RT reverse annealing of neutron irradiation resumes (or “turned on” or “un-freeze”) with same rate as that of the control detectors. This behavior would suggest some nonlinear effect, or interaction of radiation induced acceptor-type and donor-type defects.
Author
Zheng Li
(BNL)
Co-authors
Dr
Elena Verbitskaya
(Ioffe Physical-Technical Institute of Russian Academy of Sciences)
Dr
Jaakko Harkonen
(Helsinki Institute of Physics)
Dr
Jessica Metcalfe
(University of New Mexico)
Dr
Jim Kierstead
(BNL)
Dr
Martin Hoeferkamp
(University of New Mexico)
Dr
Rubi Gul
(BNL)
Prof.
Sally Seidel
(University of New Mexico)
Dr
Vladimir Eremin
(Ioffe Physical-Technical Institute of Russian Academy of Sciences)