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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24 2. Operation and Radiation Damage <strong>of</strong> Silicon Detectorsments <strong>in</strong> the laboratory were taken at 5 CandFDV as obta<strong>in</strong>ed from 10 kHz measurementwere used <strong>for</strong> comparison. Measurements at the reactor (i.e. dur<strong>in</strong>g and early after ir<strong>radiation</strong>)were however taken at the ir<strong>radiation</strong> temperature and were aected by thisphenomenon. A more detailed description <strong>of</strong> measur<strong>in</strong>g methods used <strong>in</strong> this work canbe found <strong>in</strong> section 3.5.2.2 Radiation Induced DefectsDamage caused by <strong>radiation</strong> can be divided <strong>in</strong>to two groups, surface <strong>damage</strong> and bulk<strong>damage</strong>. Due to the <strong>in</strong>terest <strong>of</strong> electronic <strong>in</strong>dustry, the surface <strong>damage</strong> is better understoodand can be controlled to a certa<strong>in</strong> extent by proper design and manufactur<strong>in</strong>gprocess. Surface <strong>damage</strong> ma<strong>in</strong>ly manifests as charge accumulation <strong>in</strong> the oxide andsubsequent breakdown. Charge accumulation at the <strong>silicon</strong>-oxide <strong>in</strong>terface signicantlydecreases the <strong>in</strong>ter-strip resistance <strong>of</strong> microstrip <strong>detectors</strong>. There<strong>for</strong>e the signal has to becollected very quickly to m<strong>in</strong>imise the loss due to leakage to neighbour<strong>in</strong>g strips.The bulk <strong>damage</strong> <strong>in</strong> <strong>high</strong> resistivity <strong>silicon</strong> is however much less understood. Anextensive study <strong>of</strong> the bulk <strong>damage</strong> <strong>for</strong> the purpose <strong>of</strong> experiments at <strong>high</strong> lum<strong>in</strong>ositycolliders is there<strong>for</strong>e ongo<strong>in</strong>g.In track<strong>in</strong>g <strong>detectors</strong> full depletion <strong>of</strong> the bulk is required. Accord<strong>in</strong>g to eq. 2.10,2.13 the full depletion voltage is proportional to the eective dopant concentration. S<strong>in</strong>celow operation voltages are sought to avoid breakdown and extensive heat<strong>in</strong>g, <strong>high</strong> resistivity<strong>silicon</strong> is used <strong>in</strong> track<strong>in</strong>g devices. There the concentration <strong>of</strong> ir<strong>radiation</strong> <strong>in</strong>duceddefects can be comparable or even much larger than the <strong>in</strong>itial dopant concentration.Thus construction <strong>of</strong> trackers <strong>for</strong> new large experiments, where they will operate <strong>in</strong> <strong>high</strong>ir<strong>radiation</strong> environments, demands an <strong>in</strong>tensive study <strong>of</strong> the ir<strong>radiation</strong> <strong>in</strong>duced bulkdefects and to those the further discussion is focused on.2.2.1 Defect GenerationThe energy loss by <strong>in</strong>teraction <strong>of</strong> an <strong>in</strong>com<strong>in</strong>g particle with matter can be divided <strong>in</strong>totwo parts: ionization and non-ionis<strong>in</strong>g energy loss (NIEL). Due to fast recomb<strong>in</strong>ation <strong>of</strong>charge carriers the ionis<strong>in</strong>g energy loss does not lead to bulk <strong>damage</strong>. NIEL conta<strong>in</strong>sdisplacements <strong>of</strong> lattice atoms and nuclear reactions. They both can result <strong>in</strong> long termbulk <strong>damage</strong> and will be described <strong>in</strong> the follow<strong>in</strong>g sections.