Investigation of the signal amplitude decrease in subsequent detection in irradiated silicon sensors

Abstract

Upcoming high energy physics experiments like the High-Luminosity LHC require unprecedented radiation hardness of the detectors, as well as short readout time due to high luminosity and occupancy. Silicon has proven to be extremely radiation hard, sufficient signals can be recorded at fluences above 1×1016neq/cm2. The signal formation was studied in silicon strip sensors, which have been irradiated and annealed until the phenomenon of charge multiplication occurred. In previous studies it was observed that the detection of subsequent signals separated up to several microseconds is altered by the charge trapped during the proceeding pulses. In this paper, the investigation of the effects due to previously created charge in subsequent pulse detection is investigated. A decrease of signal pulse amplitude, which originates from effects of the flowing charges on the electric field configuration, is observed using irradiated diodes measured with top-TCT. The decrease can be explained by polarization, which is caused by trapped charges and is well known in larger band-gap materials like diamond, but often neglected for silicon at this relatively high temperature. The polarization mechanisms happening in the sensor are described by a theoretical model and additionally supported by simulations. The initial electric field and therefore the bias voltage, the time delay between subsequent pulses and the amount of initially created charge have a large impact on this phenomenon.