Computational modelling of semiconducting X-ray detectors

The design of high-performance semiconductor detectors is dominated by requirements on position and energy resolution and speed of operation, We investigate the contribution that three-dimensional transient device modelling can make to understanding these and the potential for its use in the design cycle. Simulations are performed using the EVEREST software to solve the drift-diffusion equations. Extra functionality has been added to allow the generation of electron-hole pairs by, for example, the absorption or an X-ray. Careful time integration can measure the time of arrival of the charge packet at the collecting well. By time integrating the current arriving in the collecting well the spatial distribution of charge can be determined. A simple analytic theory is developed and compared with simulations of a large pixel detector. Comparisons with simulations of a two pixel device show that the analytic approximation is reasonable if the X-ray is absorbed beyond 100 mum from the well. but events closer show a marked deviation. (C) 2002 Elsevier Science B.V. All rights reserved.