Simulation of charge drift in surface doped, pixelated micro-structured semiconductor neutron detectors

A semiconductor neutron imaging device is proposed (X-MSND) based on high efficiency, Micro-structured Semiconductor Neutron Detector (MSNDs) bump bonded onto a Timepix pixelated readout chip. The device serves as a combined neutron and photon imager with a 256x256 pixel array, using per-pixel time-over-threshold (ToT) energy deposition. A method of simulation was developed by combining finite-element tools (COMSOL), particle transport code (Geant4), and charge transport code (Allpix2), to model the time-dependent charge induction on pixel electrodes to be read-out by the Timepix. Pixel cluster events have been simulated as a result of incident neutron irradiation for the X-MSND and compared to a planar coated diode device. The X-MSND design produced thermal neutron detection efficiency of 14%, significantly greater than the theoretical maximum for planar devices. Simulated pixel clusters showed similar qualitative characteristics as planar neutron sensitive Timepix hybrid detectors.