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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2. Operation and Radiation Damage <strong>of</strong> Silicon Detectors 29~0.17 eV(- , 0) ~0.23 eV(= , - )~0.1 eV(- , 0)~0.17 eV ~0.09 eV(- , 0)(- , 0)Ec~0.4 eV(-, 0)~0.41 eV(- , 0)~0.25 eV(+ , 0)~0.5 eV (- , 0)~0.41 eV(- , 0)~0.28 eV(+ , 0)~0.38 eV(+ , 0)Ci - CsEiVPVOV2V2OV30CiCi-Oi~0.11 eV(- , 0)~0.05 eV (+ , 0)EvFigure 2.7: Energy levels <strong>of</strong> some vacancy and carbon related defects. The defect charge statesare shown <strong>in</strong> brackets, e.g. m<strong>in</strong>us and neutral (-,0). Above the dotted l<strong>in</strong>e the energy <strong>of</strong> thetrap is written <strong>in</strong> the lower half E V and <strong>in</strong> the upper half E C . Sign = means the doublecharged state. In the gure, data from [14] were used.from defects with energy levels close to the middle <strong>of</strong> the bandgap. While standarddop<strong>in</strong>g materials (P , B) have energy levels close to the conduction (donors) or valenceband (acceptors) this is not the case with the ir<strong>radiation</strong> <strong>in</strong>duced defects (gure 2.7). Thismeans that <strong>radiation</strong> <strong>in</strong>duced defects can contribute a major part <strong>of</strong> the leakage currentgenerated <strong>in</strong> the depleted region.S<strong>in</strong>ce the defect density is proportional to the total uence (N def = g def withg def the defect generation rate) and the generation current proportional to mid-gap defectconcentration (eq. 2.35, 2.38), also the ir<strong>radiation</strong> <strong>in</strong>duced leakage current is proportionalto the equivalent uence eqIV = eq (2.50)where is the leakage current <strong>damage</strong> constant and V the volume.2.3.2 Eective Dopant ConcentrationThe eective dopant concentration N eff is composed <strong>of</strong> ionised shallow levels (donorsand acceptors) and deep levels. Be<strong>for</strong>e ir<strong>radiation</strong>, the concentration <strong>of</strong> deep levels isnegligible and the eective dopant concentration is determ<strong>in</strong>ed by the dierence <strong>of</strong> donorand acceptor concentrations Neff 0 = N D 0 ; N A 0 . Dur<strong>in</strong>g the ir<strong>radiation</strong> two types <strong>of</strong>processes take place. One is the <strong>in</strong>troduction <strong>of</strong> new defects that may act either asdonors or acceptors and the second is the removal <strong>of</strong> <strong>in</strong>itial shallow levels by creation <strong>of</strong>