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Radiation hardness of Si-sensors N.Zamjatin, JINR, Dubna

Radiation hardness of Si-sensors N.Zamjatin, JINR, Dubna. The 3rd Work Meeting of the CBM-MPD STS Consortium “Technical challenges of the CBM and MPD Silicon Tracking Systems 2009” 1 – 4 June 2009, Doctor Winter’s Lodge Resort, Sortavala, Karelia, Russia. Radiation damage of Si:

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Radiation hardness of Si-sensors N.Zamjatin, JINR, Dubna

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  1. Radiation hardness of Si-sensors N.Zamjatin, JINR, Dubna The 3rd Work Meeting of the CBM-MPD STS Consortium “Technical challenges of the CBM and MPD Silicon Tracking Systems 2009” 1 – 4 June 2009, Doctor Winter’s Lodge Resort, Sortavala, Karelia, Russia

  2. Radiation damage of Si: Removing of the atom Si from crystal lattice with vacancy on stital (V) and interstitalSi (I ); V and Iis electrical activity deep levels: V V; VО; VР; IС; IVР; et al. Deep level effects: - generation/recombination - «traping/detrapinge-h» - removing donors Main effects in Silicon at Non Ionization Energy Loss (NIEL) Ес е DL h Ev Compensation donors Dark current Charge collection 3-rd meeting CBM-MPD, 1-3 June'09

  3. A. The detector leakage current increases linearly with hadrons fluence: • =II  V • fluency, Vthe detector bulk, • I =(51)10-17 Асм-1for fast neutronsat • T = +20º C(no self-annealing) • Possible solution at high hadrons fluence: • work at low temperature -(30-50)°C, detector leakage current doubles it’s value every 8 degrees; • Detectors module design required very good thermo contact between Si-sensor and cooling plate for the excluding of the heating and thermo break down /3/ 3-rd meeting CBM-MPD, 1-3 June'09

  4. I-V and C-V measurements for detector RWS-01/01-69-7 before and after neutrons /3/ irradiation 4.9×1014 n/cm2 • Blue color curves – measurements at +20°C before irradiation • Red color curves – measurements at -28°C after irradiation • Topology of detector: • 32-p+strips; • 63×63×0.3 mm3; • 5 kOhm×cm n-type Si-Wacker, <111> 3-rd meeting CBM-MPD, 1-3 June'09

  5. До облучения: Рдет=10-6А×150В=1.5×10-4Вт (Для Vdet=(63×63×0.3)мм3). После 5 лет (CMS/SE Фn=1014 см-2): Рдет=5×10-4А×500В=0.25Вт (при Т = -5º). ! Проблема теплового пробоя (саморазогрев облученного детектора) 7.5. Рост мощности рассеяния на ППД (P=IV). 3-rd meeting CBM-MPD, 1-3 June'09

  6. B.Decreasing of the charge collection efficiency (CCE) with increasing hadrons fluence • The CCE decreases 8%/1014 n/cm2 and does not depend on initial silicon type, extrapolation of this curve to 1015 n/cm2 give the value for signal equal 20% from initial amplitude /3/ • What to do??? • to change of Si-planes after each 5×1014 n/cm2???; • to work with (20-10)% of CCE; • to work at low temperatures and at forward bias (experience of RD39, LAZARUS effect /1/ ) 3-rd meeting CBM-MPD, 1-3 June'09

  7. C.The detector full depletion voltage Ufd increases with hadrons fluence (after point inversion of type conductivity for n-type Si). This effect could be diminished /2, 4/ applying the oxygenated Si and low resistivity Si as a starting detectors material: CZ (MCZ) has higher oxygen concentration in crystal ingot, low resistivity material (100 – 800 Ohm  cm) FZ-Si-p – no conductivity type inversion FZ-Si-(n- or p-type) + O2 during the detectors technology fabrication Remark:in the real experiments with irradiated detectors Ud>Ufd for the attainment of plato CCE=f(Ud) and max S/N 3-rd meeting CBM-MPD, 1-3 June'09

  8. Inversion of bulk type conductivity (n-type to p-type) at irradiation Si-sensors • Sensor (20×20×0.4) mm3at biasUd=15Virradiated by fast neutrons • Capacity of detector measured (F=1 кГц) directly at irradiation on the neutrons chanel • Initial parameters of Si: • n-type, <111>, (FZ-Wacker); • ρ=6 кОm×сm(Ufd=80 В) • Point inversion for this detector equal (2÷3)×1012n/сm2 Direct method for the measuring of the point inversion bulk type conductivity/5/ 3-rd meeting CBM-MPD, 1-3 June'09

  9. Is it an alternative to SILICON to construct a detector with large area in radiation hard environment??? Possible candidates: CVD-C, CdTe, GaAs and??? CVD-C: (-) commercial wafers with big area???, big cost, small (50-150mkm) CCLength; (+) radiation hardness!!! CdTe(CdZnTe): (-) small area of wafers (1-5 cm2); high cost (5-10 $/mm3) for mono crystal; (+) high radiation condition of policrystaline (CERN-R&D for luminosity monitor) GaAs: (-) more expensive that Si-detectors, mechanical conditions lower that Si; (+) bigger radiation hardness that Si! (need to study of rad.hard. for real detectors) 3-rd meeting CBM-MPD, 1-3 June'09

  10. n+ strips p+ stop rings DS-strip detector: n+side with p+stop ring/n+strip 3-rd meeting CBM-MPD, 1-3 June'09

  11. DS-strip sensors need to study (surface) radiation effects on the both sides What difference between n+ and p+ sides for DS-strip sensors? • each n+ strip isolated by p+ stop ring • inter n+ strip region need bigger value of full depletion voltage in compare with bulk depletion • with over depletion increase electric field in inter n+strip region and possible break down n+ strip to p+ stop ring • detectors from difference manufactures have individual parameters (thickness of dielectric layers, density of charge in SiO2, profile of implantation layers, et al) 3-rd meeting CBM-MPD, 1-3 June'09

  12. (I-V)at +20° for Si PAD-detector (8×8×0.3 mm3) after irradiation 2×1012 alpha/cm2, Eα=3.5 MeV, α-particles illuminated n+ side (Ohmic contact) U full depletion 3-rd meeting CBM-MPD, 1-3 June'09

  13. (I-V) for Si PAD-detector (8×8×0.3 mm3) after irradiation 2×1012 alpha/cm2, Eα=3.5 MeV, α-particles illuminated p+ side (junction contact) 3-rd meeting CBM-MPD, 1-3 June'09

  14. References: • V.G.Palmieri et al., “Evidence for charge collection efficiency recovery in heavily irradiated silicon detectors operated at cryogenic temperatures”, NIM A 413 (1998) 475-478. • B.Dezillie, Z.Li et al., “Improved Neutron Radiation Hardness for Si-detectors: Application of Low Resistivity Starting Material and/or Manipulation of Neff by Selective Filling of Radiation-induced Traps at Low Temperatures”, IEEE Transactions on Nuclear Science, Vol.46, No.3, June 1999. • Ph. Bloch, N.Zamiatin et al. “Performance of Si sensors irradiated to • 5 ×1014 n/cm2”, NIM A517 (2004) 121-127. • RD-48, ROSE Collaboration Reports. • 5. Н.И. Замятин и др., Экспериментальный метод определения инверсии n–типа проводимости кремния при облучении быстрыми нейтронами. Сообщение ОИЯИ, Р13-2001-281. 3-rd meeting CBM-MPD, 1-3 June'09

  15. Conclusion: • Bulk damage effects in Si crystal are very good study and understood (big experimental data of ROSE collaboration for LHC experiments, RD48) • Surface damage effects dependent from topology and technology sensors (inter strip distance, p+ stop ring on n+ side, thickness of SiO2, et all) • DS-strip sensor need to study radiation hardness for both sides n+ and p+ before- and after point inversion (inter strip resistance, inter strip capacitance, cross talk, S/N, break down on p+ or n+ side?) • Sensors after high hadron fluence need very good thermo contact with cooling system (special design modules/ladders) 3-rd meeting CBM-MPD, 1-3 June'09

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