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

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_r) and full depletion voltage (V_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_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 10¹³ cm^-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 (≈6.4×6.4 cm² ) 80 μm 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 3·10¹⁴ cm^-2 . We present results both before and after irradiation demonstrating the feasibility of using such devices at the Large Hadron Collider (LHC) at CERN