Prolonged signals from silicon strip sensors showing enhanced charge multiplication

摘要

P-type silicon strip sensors have been irradiated and annealed to predict their performance as particle detectors. After long annealing times and at high voltages, the charge collection increases due to charge multiplication and an unexpected slow signal collection was observed. In addition to beta source measurements, an edge-transient current technique was used to investigate the origin of these slow pulses. It was discovered that sensors showing slow pulses exhibit a low but substantial electric field even beyond the high field region beneath the implants. Here, the created free electrons spread while slowly traveling to the depletion region. They subsequently get multiplied and create a broad secondary cloud of free holes, which moves toward the sensor backplane. Trapping is suspected to play a crucial role in reducing and slowing down the carrier drift. The features of the signal pulses also indicate that the large amount of free charge carriers created leads to a self-screening effect and behaves like a plasma. The results are correlated well with the observation of a ballistic deficit and an enlarged cluster size observed in charge collection measurements. The conclusions drawn by this investigation can be extended to every semiconductor detector exploiting enhanced charge multiplication but having low field regions. Published under license by AIP Publishing.