Study of radiation damage in silicon detectors for high ... - F9
Study of radiation damage in silicon detectors for high ... - F9
Study of radiation damage in silicon detectors for high ... - F9
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104 6. Inuence <strong>of</strong> Bias Voltagebias<strong>in</strong>g schemes are consistent with the assumption that electric eld <strong>in</strong>uences timedevelopment <strong>of</strong> defects created dur<strong>in</strong>g the ir<strong>radiation</strong> and not their <strong>in</strong>troduction rates.When the bias voltage is switched o, the dierence starts to anneal. The timedependence is consistent with two exponentially decay<strong>in</strong>g defects. Contributions <strong>of</strong> eachdefect type agree <strong>for</strong> samples annealed at -7 C and 5 C (about 20% <strong>for</strong> the fast andabout 70% <strong>for</strong> the slow component). They however dier <strong>for</strong> the sample annealed at 20 C(about 40% <strong>of</strong> each component). More systematic studies are there<strong>for</strong>e necessary be<strong>for</strong>erm conclusions on this eect can be made. Decay times at 20 C are about 40 h <strong>for</strong> thefast component and six weeks <strong>for</strong> the slow one. Time development <strong>of</strong> the dierence canbe scaled to other temperatures us<strong>in</strong>g activation energies. First measurements <strong>of</strong> thosewere per<strong>for</strong>med giv<strong>in</strong>g activation energies <strong>of</strong> E 1 = 0:54 0:15 and E 2 = 0:47 0:15 <strong>for</strong>the fast and slow component, respectively.As <strong>detectors</strong> <strong>in</strong> the LHC environment can be left unbiased <strong>for</strong> a signicant portion<strong>of</strong> time, a proper bias<strong>in</strong>g and temperature scheme could reduce the observed eect. S<strong>in</strong>ceit takes more than a month at 20 C to anneal out 90% <strong>of</strong> the dierence, the planned14 days at 17 C will not be sucient. And s<strong>in</strong>ce the activation energy <strong>for</strong> the slowdecrease <strong>of</strong> the bias <strong>in</strong>duced dierence is about twice lower than <strong>for</strong> the reverse anneal<strong>in</strong>g,prolonged warm periods would <strong>in</strong>uence reverse anneal<strong>in</strong>g stronger than anneal<strong>in</strong>g <strong>of</strong> thebias dependent dierence. The rema<strong>in</strong><strong>in</strong>g 8 monthsat-7 C when the detector will not beoperat<strong>in</strong>g and can be kept without bias, amount onlyto about half <strong>of</strong> the lifetime <strong>of</strong> theslow component. Due to long operation time and low ir<strong>radiation</strong> ux this can howeversuce to remove most <strong>of</strong> the eect. The bistable component may, on the other hand,amount to a signicant <strong>in</strong>crease <strong>of</strong> the full depletion voltage dur<strong>in</strong>g the operation periods.A detailed study <strong>of</strong> the bias voltage eect is thus necessary. The data it will provideshould be used to develop a scheme that will m<strong>in</strong>imise the <strong>in</strong>uence <strong>of</strong> bias eect andreverse anneal<strong>in</strong>g.