Investigation of epitaxial silicon layers as a material for radiation hardened silicon detectors

Epitaxial grown thick layers (>100 μm) of high resistivity silicon (Epi-Si) have been investigated as a possible candidate of radiation hardened material for detectors for high-energy physics. As grown Epi-Si layers contain high concentration (up to 2·10¹² cm^-3) of deep levels compared with that in standard high resistivity bulk Si. After irradiation of test diodes by protons (E _p=24 GeV) with a fluence of 1.5·10¹¹ cm^-2, no additional radiation induced deep traps have been detected. A reasonable explanation is that there is a sink of primary radiation induced defects (interstitial and vacancies), possibly by as-grown defects, in epitaxial layers. The “sinking” process, however, becomes non-effective at high radiation fluences (10 ¹⁴ cm^-2) due to saturation of epitaxial defects by high concentration of radiation induced ones. As a result, at neutron fluence of 1·10¹⁴ cm^-2 the deep level spectrum corresponds to well-known spectrum of radiation induced defects in high resistivity bulk Si. The net effective concentration in the space charge region equals to 3·10¹² cm^-3 after 3 months of room temperature storage and reveals similar annealing behavior for epitaxial as compared to bulk silicon