Experimental study of pre-diffusion in MultiLinear Silicon Drift Detectors

Multilinear silicon drift detectors (MLSDD) are silicon drift detectors in which signal electrons are confined within parallel drifting columns at few micrometers from the anodes' surface and transported towards point-like anodes by the electrostatic field. During the initial motion across the thickness, lasting a few tens of ns, the signal electrons spread in all directions to a given width - called pre-diffusion - until the signal electrons are focused in the drift channels and further spread into adjacent channel is suppressed. This work is devoted to the study of the initial motion of the electron cloud when the electrons are being focused toward the minimum of the potential energy in order to evaluate the achievable performance in different applications ranging from high-resolution high-rate X-ray spectroscopy to particle tracking with very high position resolution to fast 2-D X-ray imaging. We carried out a measurement campaign to evaluate the impact of the detector operating conditions and of the charge injection level on the initial charge spread.