Analysis of trapping effects on charge transfer in proton irradiated pn-CCDs

A new type of Charge Coupled Device, a pn-CCD, was developed for the European Photon Imaging Camera (EPIC) on the X-ray Multi Mirror (XMM) satellite mission of the European Space Agency. The detector for fast X-ray imaging and spectroscopy uses pn-junctions instead of the traditional MOS-gates. To prove the detector radiation hardness, four pn-CCDs were irradiated with 10 MeV-protons of fluences ranging from 6.0 × 108 up to 6.5 × 109 cm−2. The equivalent 10 MeVproton fluence is estimated at 3.6 × 108cm−2 for the ten year satellite mission. It turned out that the Charge Transfer Efficiency is the most irradiation sensitive detector parameter. The trap dependent charge transfer is described by a Monte Carlo simulation model which considers all relevant parameters. The simulations agree well with the results of the measurements. This method was also applied for defect analysis. The predominant radiation induced defect type was identified as a vacancy-oxygen trap, called A-centre0/−. The result is confirmed by Deep Level Transient Spectroscopy (DLTS) measurements and annealing experiments.