Accelerated annealing of n⁺-p strip detectors irradiated with pions

Abstract

Charge collection measurements with silicon detectors with implanted n-type readout strips in p-type silicon bulk (n + -p) are presented. Detectors were irradiated with 191 MeV pions at the Paul Scherrer Institute (PSI) in Villigen in Switzerland. Signals induced by electrons from 90 Sr source were measured with SCT128 chip. Collected charge and detector current were measured after several annealing steps summing up to over 10000 minutes at 60 ˚C. It was observed that irradiation of these detectors with pions results in only ∼30% of the increase of V fd seen after irradiation with neutrons to the same NIEL equivalent fluence. Charge multiplication effects in pion irradiated detectors were seen only after long accelerated annealing time. Both effects are consistent with smaller space-charge introduction rates after irradiation with charged hadrons, characteristic for oxygenated detector material. It was confirmed that, at sufficient bias voltage, reverse annealing after pion irradiation does not represent a problem for application of these detectors in trackers at upgraded LHC.

Effects of accelerated long term annealing in highly irradiated n+-p strip detector examined by Edge-TCT

“…On the other hand, at high bias voltages the charge increases after same annealing periods. This is consistent with previous reports of increased charge collection after long term annealing at high bias voltage in heavily irradiated detectors [12,13]. This effect has to be ascribed to the changes of the electric field profile due to variations of the effective space charge during annealing.…”

“…The first remarkable effect is a nearly threefold increase of the collected charge in the region near the strips (figure 6a) where the electric field is the highest. This increase is due to rising of the space charge concentration at the n + -p junction with the annealing time, leading to an increase of the electric field, beyond the E >∼ 12 V/µm [13,24,25], where the impact ionization takes place. This happens between 320 min and 640 min of annealing time for the highest voltage applied.…”

“…Studies with silicon planar detectors having n-side readout show unexpectedly good charge collection efficiency (CCE), sufficient for successful operation even at extreme hadron fluences, such as those expected in the innermost detector layers at the upgraded LHC [2][3][4][5][6][7][8][9][10][11]. It is generally accepted [12,13] that the process of charge multiplication leads to higher CCE. Multiplication occurs at sufficient bias voltages due to the very high electric field near the n + -p junction, which is a result of the effective space charge (N eff ) increase with irradiation fluence.…”

Displacement Damage in Silicon Detectors for High Energy Physics

“…A further striking feature of 300-μm-thick n-in-p strip sensors is that-contrary to p-in-n sensors of same thicknessthe collected charge for highly irradiated detectors is less dramatically influenced by the reverse annealing of the effective space charge [16], [77], [78]. This is, for example, shown in Fig.…”

Bistability of the BiOi complex and its implications on evaluating the “acceptor removal” process in p-type silicon

“…High Voltage CMOS sensors) [6,7]. Radiation effects in these devices were surveyed mainly at macroscopic level, by monitoring their electrical performance after irradiation with different particles of various fluence levels and the changes during annealing at moderate temperatures (60, 80 °C) [8][9][10][11]. The latter is important for planning running scenarios as well as for quantitatively predicting the effects of the annealing on operation if unplanned events occur.…”