Dynamics of charge collection in pixelated semiconductor sensor studied with heavy ions and Timepix

This paper presents a novel technique allowing for the measurement and visualization of the spatial distribution and time evolution of the charge collection process in semiconductor sensors of ionizing radiation. The study was carried out with a pixelated high resistivity silicon sensor bump-bonded to the Timepix readout chip (256 × 256 pixels, with pitch of 55 μm). The sensor was irradiated with energetic protons (132 MeV) and carbon ions (240 MeV/u) entering the sensor at shallow angles. Such ions penetrate the full sensor thickness ionizing and depositing charge along their tracks. The charge deposited is collected by individual pixels of the Timepix chip operated in Time mode. The overall accuracy of these measurements was enhanced by averaging many particle tracks. The time accuracy is in order of nanoseconds and the position accuracy is about 5 μm. The purpose of this work is to demonstrate the accurate measurement that may be used with the mathematical model to investigate the electric field profile in a semiconductor sensor.