Charge transport and signal generation in CdTe pixel detectors

The current and charge signals on individual pixels of CdTe gamma-ray cameras are calculated. The time and position dependent free carrier densities following the absorption of a gamma-ray in the detector are first calculated by solving the continuity equations. These density distributions are then combined with the physical electric field and the pixel weighting field to provide the current induced through an individual pixel from which the charge signal is also obtained. Simulations are made for various pixel sizes. These simulations confirm that the energy resolution of electron collecting pixel detectors must improve when smaller pixels are used since small pixels are less sensitive to holes.