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Study of radiation damage in silicon detectors for high ... - F9

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2. Operation and Radiation Damage <strong>of</strong> Silicon Detectors 27Primary Vacancies Primary Interstitials Replaced impuritiesGroup AV +P! VP I+VP ! P C i + C s ! C i -C sV +O! VO I+VO ! O C i + O i ! C i -O iV +VO ! V 2 O I+V 2 ! V C i + P s ! C i -P sV +C i ! C s I+C s ! C iV +V 2 O ! V 3 O I+V 3 O ! V 2 OV 2 + V ! V 3Group BV +V! V 2 I+V ! SiV 2 + V ! V 3Table 2.1: Survey <strong>of</strong> possible defect reactions. Group A reactions are caused by diusion <strong>of</strong><strong>in</strong>terstitials and vacancies throughout the crystal. To group B belong the reactions, which havea signicant chance <strong>of</strong> occurr<strong>in</strong>g dur<strong>in</strong>g a primary cascade. Indexes i and s stand <strong>for</strong> <strong>in</strong>terstitialand substitutional.2.2.3 Types <strong>of</strong> DefectsAt the <strong>in</strong>teraction <strong>of</strong> the travers<strong>in</strong>g particle with the lattice an <strong>in</strong>terstitial-vacancy pair(Frenkel pair) or a cluster can be produced, depend<strong>in</strong>g on energy, transferred to the primaryatom. Though physical properties <strong>of</strong> clusters are not determ<strong>in</strong>ed yet, theoreticalmodels have been proposed [23]. In the rst phase the disordered region consists <strong>of</strong> many<strong>in</strong>terstitials and vacancies. Most <strong>of</strong> the vacancies and <strong>in</strong>terstitials recomb<strong>in</strong>e, some vacanciesmay <strong>in</strong>teract to <strong>for</strong>m stable divacancies or <strong>high</strong>er vacancy complexes while therest diuse away. Those can react with other <strong>radiation</strong> <strong>in</strong>duced defects, <strong>for</strong>m<strong>in</strong>g defectcomplexes, or react with impurity atoms such as carbon, oxygen and phosphorus, thosebe<strong>in</strong>g among the most common impurities <strong>in</strong> <strong>silicon</strong>. When only a Frenkel pair is createdonly reactions with exist<strong>in</strong>g defects are possible. Thus reactions <strong>of</strong> the defects can be divided<strong>in</strong>to two groups. In the group A are reactions <strong>of</strong> vacancies and <strong>in</strong>terstitials dius<strong>in</strong>gthroughout the crystal. Group B reactions only have a signicant chance <strong>of</strong> occurr<strong>in</strong>gwith<strong>in</strong> the cluster, where the defect density is<strong>high</strong>.Possible reactions <strong>of</strong> both groups arelisted <strong>in</strong> table 2.1 and the most relevant defect congurations are shown schematically <strong>in</strong>gure 2.6.2.3 Eects on Bulk PropertiesDefects generated dur<strong>in</strong>g the ir<strong>radiation</strong> have the follow<strong>in</strong>g eects on the bulk properties: They <strong>in</strong>troduce new energy levels <strong>in</strong> the band gap, contribut<strong>in</strong>g to emission and

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