Title: Simulation study of signal formation in position sensitive planar p-on-n silicon detectors after short range charge injection,
Abstract: Segmented silicon detectors (micropixel and microstrip) are the main type of
detectors used in the inner trackers of Large Hadron Collider (LHC) experiments
at CERN. Due to the high luminosity and eventual high fluence, detectors with
fast response to fit the short shaping time of 20 ns and sufficient radiation
hardness are required.
Measurements carried out at the Ioffe Institute have shown a reversal of the
pulse polarity in the detector response to short-range charge injection. Since
the measured negative signal is about 30-60% of the peak positive signal, the
effect strongly reduces the CCE even in non-irradiated detectors. For further
investigation of the phenomenon the measurements have been reproduced by TCAD
simulations.
As for the measurements, the simulation study was applied for the p-on-n
strip detectors similar in geometry to those developed for the ATLAS experiment
and for the Ioffe Institute designed p-on-n strip detectors with each strip
having a window in the metallization covering the p$^+$ implant, allowing the
generation of electron-hole pairs under the strip implant. Red laser scans
across the strips and the interstrip gap with varying laser diameters and
Si-SiO$_2$ interface charge densities were carried out. The results verify the
experimentally observed negative response along the scan in the interstrip gap.
When the laser spot is positioned on the strip p$^+$ implant the negative
response vanishes and the collected charge at the active strip proportionally
increases.
The simulation results offer a further insight and understanding of the
influence of the oxide charge density in the signal formation. The observed
effects and details of the detector response for different charge injection
positions are discussed in the context of Ramo's theorem.