Intrinsic spatial resolution of semiconductor X-ray detectors: a simulation study

We have investigated the intrinsic limitation of the spatial resolution of a directly absorbing semiconductor detector. The primary interaction of an incident X-ray quantum is followed by a series of processes that generate Compton or fluorescence photons and subsequent electrons. Their ranges determine the spatial resolution of the detector, expressed in terms of the modulation transfer function. The effects of carrier transport have been neglected in this work. Monte Carlo simulations have been carried out in the 10-100 keV energy range with the program, ROSI (Roentgen Simulation), which is based on the well-established EGS4 algorithm. On a fine grid, the lateral distribution of deposited energy has been calculated in typical materials such as Se, CdTe, HgI2 and PbI2. The results can be used to either determine the point spread function of an energy-integrating detector, or to study multiple registration in adjacent pixels of photon-counting detectors. The results show that the complex absorption process determines the spatial resolution of the detector considerably. If a very high spatial resolution is required, a well-adapted semiconductor should be applied. Dependent on the energy range used, lists of favorable materials are given. At energies above 50 keV, Compton scattering reduces spatial resolution in the high frequency range. (C) 2004 Elsevier B.V. All rights reserved.