Modelling CCDs for X-ray detectors using three-dimensional semiconductor device modelling software

The three-dimensional drift-diffusion equations are used to model the behaviour of a charge-coupled device when an X-ray strike creates a cloud of free carriers. The transport of the charge cloud to the collecting potential well is studied, and the lateral diffusion of charge compared with a simple analytic model. The results of this can be used to predict the performance of a device, particularly the active area of a pixel. Comparison of the results obtained from a simple structure with those from a more realistic device shows that the simple results are valid for X-ray strikes below about 100 μm from the well, but that more realistic, and more computationally expensive, simulation is necessary for accurate solutions closer to the well.