Speaker
Jessica Metcalfe
(University of New Mexico)
Description
For the development of radiation-hard Si detectors for the SiD BeamCal program for ILC, n-type MCZ Si detectors have been irradiated first by fast neutrons to fluences of 1.5x10^14 and 3x10^14 neq/cm2, and then by gamma up to 500 Mrad. The motivation of this mixed radiation project is to develop a Si detector that can utilize the gamma/electron radiation that exists in the ILC radiation environment, which also includes neutrons. 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 4 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-month room temperature annealing 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 suppressing and interesting effect is that, it seems that regardless of the fluence (two in our case: 1.5x10^14 and 3x10^14 neq/cm2), the reverse annealing is totally suppressed by the same dose of gamma (500 Mrad): the full depletion voltage for the two detectors irradiated to these two different fluence stay the same before and after gamma radiation. Meanwhile, for the control detectors, the full depletion voltages have gone up by the amount of 204 V and 583 V for the two fluences, 1.5x10^14 and 3x10^14 neq/cm2, respectively. This would imply positive space charge created in these two samples are different at the same gamma dose and/or the reverse annealing is affected by gamma radiation, suggesting some non linear effect or interaction. More samples and fluences will be studied in the future to verify the effect.
Authors
Jessica Metcalfe
(University of New Mexico)
Zheng Li
(Brookhaven National Laboratory)
Co-authors
Jaakko Harkonen
(University of Helsinki)
Jim Kierstead
(Brookhaven National Laboratory)
Rubi Gul
(Brookhaven National Laboratory)
Sally Seidel
(University of New Mexico)
