Improving the radiation hardness properties of silicon detectors using oxygenated n-type and p-type silicon

Abstract

The degradation of the electrical properties of silicon detectors exposed to 24 GeV/c protons were studied using pad diodes made from different silicon materials. Standard high-grade p-type and n-type substrates and oxygenated n-type substrates have been used. The diodes were studied in terms of reverse current (I/sub r/) and full depletion voltage (V/sub fd/) as a function of fluence. The oxygenated devices from different suppliers with a variety of starting materials and techniques, all show a consistent improvement of the degradation rate of V/sub fd/ and CCE compared to un-oxygenated substrate devices. Radiation damage of n-type detectors introduces stable defects acting as effective p-type doping and leads to the change of the conductivity type of the silicon bulk (type inversion) at a neutron equivalent fluence of a few 10/sup 13/ cm/sup -2/. The diode junction after inversion migrates from the original side to the back plane of the detector. The migration of the junction is avoided using silicon detectors with p-type substrate. Furthermore, the use of n-side readout allows a better charge collection in segmented devices operated in underdepleted mode. Large area (/spl ap/6.4/spl times/6.4 cm/sup 2/) 80 /spl mu/m pitch microstrip capacitively coupled detectors with polysilicon bias resistors made on p-type substrate with a n-i-p diode structure have been irradiated up to 3/spl middot/10/sup 14/ cm/sup -2/. We present results both before and after irradiation demonstrating the feasibility of using such devices at the Large Hadron Collider (LHC) at CERN.