Alpha particle, proton and X-ray damage in fully depleted pn-junction CCD detectors for X-ray imaging and spectroscopy

The development of a novel charge coupled device, the fully depleted pn-junction CCD (pn-CCD), has been completed. It will be used as focal plane detector for X-ray imaging and spectroscopy on two scientific satellite missions, XMM and ABRIXAS. A comprehensive, quantitative study of the radiation damage in the pn-CCD was performed with 10-MeV protons, 5.5 MeV alpha-particles and soft X-rays. The irradiation by soft X-rays with a dose of 23 krad(Si) caused no performance degradation. The A-centre (oxygen-vacancy defect) and the divacancy trap were generated by particle irradiations which are both inevitably in silicon. But no other trap type affected the charge transfer in the tested operating temperature range between 75 K and 240 K. The formation probability of the dominant trap type, the A-centre, is presented for proton and alpha-particle irradiation. We have measured the effects of particle fluence and temperature on trap generation as well as the variation of trap concentration. The measured energy resolution of the irradiated pn-CCDs proves the high radiation hardness of this type of charge coupled device. The full width at half maximum of the Mn-K_α line (5894 eV) was increased from 135 eV to 175 eV (FWHM/E=3%) after exposure to a 10-MeV proton fluence of 2.10⁹ cm^-2. The results differ from that of other charge coupled devices because of the different detector concept and fabrication process