Speaker
Mr
Gabriele Segneri
(INFN Pisa and Università di Pisa, Italy)
Description
An LHC upgrade with a luminosity increase of one order of magnitude
has been recently envisaged. In this scenario, silicon detectors
produced according to the present technologies would not withstand
the increased radiation fluences.
Magnetic Czochralski silicon (MCz) can be a promising solution for
future experiments due to its high intrinsic oxygen concentration,
which improves the radiation tolerance. The INFN SMART
Collaboration, a research project within the framework of the CERN
RD50 Collaboration, recently started an R&D activity to study the
properties and the radiation hardness of this material and a
possible employment in high energy physics tracking systems.
A large set of MCz 4’’ wafers of 1 kcm resistivity of both n- and
p-type has been recently produced by Okmetic (Finland). Wafers were
then processed at ITC-IRST in Trento (Italy), with a process tuned
for low temperature steps. A few Float Zone (FZ) wafers were also
processed with the same masks and process to allow a comparison with
the present material.
The wafer layout contains a large number of multiguard diodes,
specific test structures and microstrip sensors. Pre-irradiation
properties were investigated to assess the manufacturing quality and
the bulk properties. Diodes, together with other test structures,
underwent an irradiation campaign with 24 GeV/c protons at CERN, 26
MeV/c protons in Karlshrue and nuclear reactor neutrons in
Ljubliana, up to fluences of 8x1015 cm-2.
For all diodes, the effective dopant concentration and the leakage
current were studied as a function of the annealing time at
different temperatures and, according to the fluence and the bulk
type, the type inversion could be observed. The increase in leakage
current and the effective dopant concentration were also studied as
a function of the fluence and both damage constant and beta
parameter were measured. Bulk materials and irradiation types were
also compared.
A thorough study on defects has been also performed on these diodes
via Thermally Stimulated Currents. The occurrence of a shallow donor
defect is observed in both types of material at 30 K after
irradiation at of 4x1014 cm-2. Type inversion has been also
investigated for fluences up to 1015 cm-2 by current transient
spectroscopy: results are reviewed and discussed.
Primary author
Mr
Gabriele Segneri
(INFN Pisa and Università di Pisa, Italy)
