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

Epitaxial grown thick layers (greater than or equal to 100 mu m) of high resistivity silicon (Epi-Si) have been investigated as a possible candidate for radiation hardened material for detectors in high-energy physics. As grown Epi-Si layers contain high concentrations (up to 2.10(12) 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 1.5.10(11) 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 fluences of 1.10(14)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 3.10(12) cm(-3) after 3 months of room temperature storage and reveals similar annealing behavior for epitaxial as compared to bulk silicon.