The physics of the low-energy tail in the ACIS CCD The spectral redistribution function

We studied the response of high-resistivity MOS CCDs to monochromatic X-ray illumination at energies ranging from 1.47 to 5.9 keV and discovered a new feature in the low-energy tail of the response function. We attribute it t o the photons interacting in the gate insulator and explain the shape of th e entire low-energy tail assuming that it is formed by electron charge clou ds partially formed in the gate oxide. The size of the charge clouds derive d from this model is much smaller than previously reported. This can be exp lained by a different field distribution in a buried channel CCD. (C) 2000 Elsevier Science B.V. All rights reserved.