Modeling charge collection in x-ray imagers

We present a TCAD simulation-based investigation of charge transport and charge collection mechanisms of a pinned photodiode pixel for X-ray imaging. Following static simulations to determine the electric-field and potential profiles, charge collection was analyzed with transient numerical simulations. A new, simple and computationally affordable calculation based on the extension of Ramo's theorem to account for carrier diffusion is proposed to estimate the trajectories of the generated carriers and the corresponding currents at the device terminals. The new method is validated and successfully compared to the time-dependent TCAD simulations of a p-i-n diode and a template 3D pinned photodiode.