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During studies on the signal formation in silicon strip sensors, irradiated and annealed until the occurring of the phenomena of charge multiplication, it was observed that previously flowing free carriers changed the detector response. In particular, it was inferred that trapping of free carriers produced by a laser pulse changes the electric field distribution.
The impact of subsequent laser pulses distant even several microseconds on the signals was then studied by means of Edge- and Top-Transient Current Technique. A strong reduction of the collected charge and a change in the signal shape have been observed for different laser pulse repetition times and intensities, temperatures and sensor irradiation fluences.
The results confirm that trapping processes change the electric field distribution. This phenomenon known as “polarization effect” has been observed in other materials or in silicon at very low temperatures. In this work the consequences of this effect on the measured signals are shown at operation temperatures (-15°C-30°C).