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 10(13) 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 (approximate to 6.4x6.4 cm(2)) 80 mu m pitch microstrip capacitively coupled detectors with polysilicon bias resistors made on p-type substrate with a n-in-p diode structure have been irradiated up to 3 . 10(14) 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. Large area n-type capacitively coupled detectors have also been produced with oxygenated substrate with good preirradiation characteristics. It is therefore anticipated that the use of oxygenated substrates combined with the n-in-p approach will allow operation of microstrip silicon detectors even above a dose of 10(15) protons cm(-2).