Study of charge sharing in a silicon pixel detector with heavy ionizing particles interacting with a Medipix2 device

The charge sharing effect among adjacent pixels of a Medipix2 pixel detector comes from the lateral spread of charges generated from the interaction of an ionizing particle in silicon. The charge sharing follows specific ionizing losses of particle along its track in silicon influenced by several effects that cause the lateral spread of the charge such as the plasma effect, charge column erosion and funneling on top of diffusion and drift processes in an electric field. A model that takes into account these effects has been used to fit results of cluster size measurements as a function of the bias voltage for a Medipix2 silicon pixel detector (256×256 pixels, each measuring 55 μm×55 μm×300 μm) exposed to a beam of heavily ionizing particles (protons, α-particles, carbon, and oxygen ions). Results on the response of the device to protons with different incident angles are also presented. In particular, the angular detection sensitivity measured for protons of 10 MeV is reported.