A method for non-destructive resistivity mapping in silicon detectors

It is well known that the resistivity non-uniformity of silicon detectors is a crucial parameter when pulse-shape analysis is used to identify the charge and the mass of stopped heavy ions. In this work a method is described that allows a direct absolute resistivity measurement of the detector as a function of the position (∼mm resolution). The detector is used in a reverse-mount configuration and signals are collected for various applied voltages and for various (x,y) positions by using a point excitation. For each applied voltage-position combination, the average signal risetime is obtained via a digital pulse-shape analysis, finally allowing the extraction of the desired resistivity measurement as a function of the position. The method is non-destructive and can be applied to detectors with arbitrary shapes and readout geometries. Detectors can be fully tested in the laboratory before the actual experiments, possibly rejecting before beam time those not satisfying the resistivity uniformity requirements of the experiment.