Si-detector macroscopic damage parameters during irradiation from measurements of dark current evolution of with fluence Craig Buttar, University of Sheffield collaborators P Booth, I Dawson, PJ Dervan, C Grigson, RS Harper, R Nicholson, University of Sheffield Maurice Glaser, CERN, Alick Macpherson, PSI/CERN

Craig Buttar NSS Outline Radiation damage in Si ATLAS SCT PS irradiation facility Current evolution with fluence Results from proton irradiation Pion irradiation at PSI Results from pion irradiation Summary of results-comparison to NIEL

Craig Buttar NSS Radiation effects Irradiation by heavy particles:  s, ps,… results in displacement of atoms from their lattice sites. –Linear increase in leakage current with fluence: I=  D Change in effective doping due to donor removal and acceptor creation –type inversion n  p at ~ neqcm -2 –Change in depletion voltage, primarily due to At the Large Hadron Collider Expect levels ~1.4x1014(1MeV)neqcm-2 in regions closest to interactions-central tacking region of ATLAS and CMS Detector irradiation programme at CERN PS

Craig Buttar NSS PS Irradiation setup Irradiate detectors with voltage applied at ~-7 0 C Monitor temperature and current during the irradiation between beam spills Small beam spot requires scanning of detectors Monitor fluence and uniformity of irradiation Measure fluence by activating Al foils –measure 24 Na  peak at 1369keV, T 1/2 =16hrs –Calibrate counter from secondary emission counter

Craig Buttar NSS Silicon Microstrip Detectors

Craig Buttar NSS Model of bulk current during irradiation At low fluences, depletion depth is constant => I~  Assume no annealing at ~-7 o C Depletion depth, d At high fluences, depletion depth~ =>I~ Current damage: I=  D Change in effective carrier concentration

Craig Buttar NSS Current evolution with proton fluence V b =100V

Craig Buttar NSS Proton Results-power laws High fluence gives good agreement with : Results based 90 full-size ATLAS detectors Low fluence agreement is less good with fluence rising sublinearly :

Craig Buttar NSS Proton Results-Damage parameters

Craig Buttar NSS Module currents 4 detectors in Module Use for on-line dosimetry

Craig Buttar NSS PSI-pion irradiation Πe1 beamline, T=191MeV Different operation due to beam structure-switch-off beam to take I-Vs 19ns beam with 1ns spacing Use ATLAS mini-detectors 1cm 2, from wafer with full-size detector ‘Portable’ cold box, chiller, monitoring system Guard and bulk biased seperately

Craig Buttar NSS Pion Irradiation Results

Craig Buttar NSS Summary of results 24 GeV protons300Mev pions  (+20 o C) (4.8±0.1)x Acm -1 (1.2±0.2)x Acm -1 Low fluence power law   (+20 o C) from [6,7] 2.5x Acm x cm -1  (-10 o C) 0.063±0.002cm ±0.02cm -1 High fluence power law

Craig Buttar NSS Summary A model for current evolution with fluence based on bulk current has been used to analyse detectors currents during irradiations with protons and pions The model appears to work well but there are deviations from the expected power laws Values of  and  have been extracted from the data  and  are larger than other results, but care required when comparing. Ratio of alpha agrees with relative NIEL-but need to reduce errors from fluence on pion measurements.

Craig Buttar NSS More work Improve model, why are there deviations from the power law ? Investigate effect of annealing Make measurements at other sites with a range of particle and energies