Radiation Hardening of Silicon Detectors

%RD48 %title\\ \\Silicon detectors will be widely used in experiments at the CERN Large Hadron Collider where high radiation levels will cause significant bulk damage. In addition to increased leakage current and charge collection losses worsening the signal to noise, the induced radiation damage changes the effective doping concentration and represents the limiting factor to long term operation of silicon detectors. The objectives are to develop radiation hard silicon detectors that can operate beyond the limits of the present devices and that ensure guaranteed operation for the whole lifetime of the LHC experimental programme. Radiation induced defect modelling and experimental results show that the silicon radiation hardness depends on the atomic impurities present in the initial monocrystalline material.\\ \\ Float zone (FZ) silicon materials with addition of oxygen, carbon, nitrogen, germanium and tin were produced as well as epitaxial silicon materials with epilayers up to 200 $\mu$m thickness. Their impurity concentrations were measured using SIMS and IR techniques. Single pad diodes were manufactured from these non-standard materials using either a planar or a mesa process. Their electrical and energy level defect characterization was performed before and after irradiation.\\ \\The following conclusions can be drawn from the data that has been collected over the last year:\\ \\\begin{enumerate} \item[a)] The $\beta$ parameter can be reduced by at least a factor of 2 to 3. If this can be achieved reliably then this will provide safe operation of the detectors in the LHC experiments over a ten year period. The reason for the lower $\beta$ parameter, in most cases is thought to involve the compensation level of the material and the oxygen and carbon concentrations. \item[b)] Low resistivity (1 kOhm cm) material should be used. This inverts at a higher fluence and reduces the final operating voltage after 10 LHC years. \item[c)] Oxygenated FZ made using the jet technique performs better than standard FZ if irradiated with protons. The material needs to be studied with charged pions and the reason for the NIEL violation (compared to neutrons) needs to be understood. Diffused oxygen material has been tested using neutrons and showed no improvement. This material will be tested using protons. \item[d)] Silicon-tin has been tested and needs further developments. \item[e)] CZ material looks promising and higher resistivity substrates are being investigated $-$~e.g magnetic CZ. \item[f)] Cryogenic operation looks to be a very promising way to operate silicon detectors after very high neutron fluences. \end{enumerate}