1/23/021

2 Proton Radiation Damage in High- Resistivity n-Type Silicon CCDs C. Bebek, D. Groom, S. Holland, A. Karcher, W. Kolbe, J. Lee, M. Levi, N. Palaio, B. Turko, M. Uslenghi, M. Wagner, G. Wang Lawrence Berkeley National Laboratory

1/23/023 Outline n Description of LBNL developed CCDs n Radiation damage study and measurement of charge transfer efficiency (CTE) n Identification of radiation induced traps using pocket pumping techniques n Fitting of CTE data to trap densities n Summary of results

1/23/024 LBNL CCD Technology n LBNL CCDs differ from conventional devices in that they are made from high resistivity, n-type silicon which can be fully depleted n They use buried p-channels (instead of n-channels) for charge storage and transport. Carriers are holes. n Large photosensitive volume results in a greatly enhanced near IR response. n They can be operated back illuminated without the need for thinning, resulting in a significant cost savings.

1/23/025 Radiation Testing of CCDs n Plans to employ LBNL CCDs in long term space based missions require them to have high radiation tolerance. n We performed room temperature irradiation study using 12 MeV proton doses of 5x10 9, 1x10 10, 5x10 10 and 1x10 11 p/cm 2. n Characterized the devices by measuring their CTE and dark current. n Measurements demonstrated excellent radiation tolerance superior to n-channel CCDs.

1/23/026 Charge Transfer Efficiency Calculation CTE measured by exposing CCD to 55 Fe x-rays which deposit 1620 e - per pixel X-ray peak heights are plotted vs row or column number transferred. Slope of the line fitted to the clustered single pixel events is measure of the CTE CCD irradiation dose 1x10 10 p/cm 2 measured at 125K X-ray stacking plot for analysis Parallel CTE =

1/23/027 Measured CTE vs Radiation Dose CTE vs radiation dose measured at 128K

1/23/028 CTE vs Temperature at 1x10 11 p/cm 2 Both serial and parallel CTE exhibit significant temperature dependence due to interactions with radiation induced trapping centers.

1/23/029 Pocket Pumping Illustrated Pre-radiation measurement Trap density traps/pixel Pocket pumping: 5 shifts, cycles Dose 1x10 10 protons/cm 2 Trap density traps/pixel

1/23/0210 Flatfield level Pocket pumping peak Depletion peak Saturation Pixel Value (adu) Histogram to Measure Trap Efficiency

1/23/0211 Measured Trap Effectiveness Clock overlap period = 19.5  s Peaks at 160 and 190K.

1/23/0212 Hole Traps Found in n-Type Si Si i VV + VVV CiCi CiOiCiOi CiCsCiCs Proton Irradiation Trap parameters measured using DLTS

1/23/0213 Charge Transfer Efficiency Model where The effectiveness factor, F determines the temperature range over which the trap will significantly reduce the CTE. F should also predict the shape, amplitude and location of each trap as measured in the pocket pumping experiment. We use an improved model which includes asymmetrical clocking and finite trap capture time. N t and n e are the density of traps and electrons (holes) per pixel T 0 and T p are the clock overlap and period N z distance between x-rays and  e the trap emission time

1/23/0214 Trap Effectiveness vs Temperature V-V C i C-O

1/23/0215 Trap Effectiveness vs Temperature Excellent matching of calculated and pocket pumping measurement of trap effectiveness for clock overlap time of 19.5  s. Confirms the existence of the proposed traps. V-V C i C-O

1/23/0216 Fitting Trap Concentrations to CTI

1/23/0217 Fitted Trap Density

1/23/0218 Summary n 4 LBNL p-channel CCDs proton irradiated at 12 MeV and doses up to 1x10 11 p/cm 2. n Measurements show they are significantly more radiation resistant than n-channel CCDs. n Pocket pumping experiments identified primary trapping centers impacting CTE. n Fit of CTE to trap concentrations shows good agreement with radiation dose. n Results will help us to predict and perhaps enhance long term performance in radiation environment.

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