Improvements in Modeling of Diffusion-Limited Point Spread Function in Solid-State Detectors

The intrinsic resolution of a solid-state detector such as a CCD is often dominated by diffusion of photogenerated charges. The resolution for imaging detectors has been successfully predicted using the Blouke-Robinson model, which calculates a modulation-transfer-function curve in the spatial-frequency domain. For applications that image point-source objects, the shape of the point spread function (PSF) is a more appropriate tool for modeling the detector performance. A direct calculation of charge-carrier diffusion developed by Widenhorn provides the needed mathematical model, but it suffers from some practical difficulties in its calculation involving singularities and slow convergence of the series. We present an equivalent model and implementation that converges rapidly in all cases of interest. Predictions of this PSF model are compared against Monte Carlo simulations of carrier transport.