Simulation of charge multiplication and trap-assisted tunneling in irradiated planar pixel sensors

We present a model for the TCAD simulation of charge multiplication and trap-to-band tunneling to explain the discrepancies between the experimentally observed charge collection in highly irradiated planar pixel sensors and the predictions made using the Hamburg model. DC and transient TCAD simulations of one dimensional n-in-p diodes were performed and reproduce well the observed behavior of diode irradiated to fluences of the order of 10^15-16 n_eq cm^-2. The results of the simulations show that impact ionization and de-trapping due to tunneling qualitatively explain the behavior of irradiated sensors observed experimentally.