The X-ray energy response of silicon. Part A. Theory

In this, the first part of a two-part study of the interaction of soft X-rays with silicon, motivated by the calibration requirements of CCD imaging spectrometers in astronomy, we describe a Monte Carlo model of X-ray energy loss whose products are the energy- and temperature-dependences of (i) W, the average energy required to create an electron-hole pair, and (ii) the Fano factor F. W and F have invariably been treated as material constants in previous analyses of Si X-ray detector performance. We show that in fact, at constant detector temperature T, W is an increasing function of X-ray energy for E<0.5 keV while F is predicted to increase slowly with E. The temperature coefficient dW/dT has a calculated value similar 1x10-4 K-1 at a typical CCD operating temperature of 170 K. We discuss the practical implications of these results. Finally, we describe our separate calculations of the near-edge variation of CCD quantum detection efficiency arising from silicon K-shell Extended X-ray Absorption Fine Structure (EXAFS). ((orig.))