Studies of the radiation hardness of oxygen-enriched silicon detectors

Detectors of high-energy particles sustain substantial structural defects induced by the particles during the operation period. Some of the defects have been found to be electrically active, degrading the detector's performance. Understanding the mechanisms of the electrical activities and learning to suppress their influence are essential if long 'lifetime' detectors are required. This work report s about radiation hardness of silicon P-I-N devices fabricated from oxygen-enriched, high-resistivity material. The high and nearly uniform concentration of oxygen in float-zone silicon has been achie ved by diffusion of oxygen from SiO2 layers

Study of the evolution ot the active volume in irradiated silicon detectors

Red (670 nm) LED light was used to study the charge collection properties of non-irradiated and irradiated n-type silicon detectors. The advantages of red LED, compared to low-range alpha particles, are the availability of an external trigger, and a very shallow distribution of the created electron-hole pairs (< 10 µm). These features, combined with the use of a fast current amplifier and a 2.5 G s/s sampling oscilloscope, allow the electric field evolution in irradiated detectors to be studied. Evidence of a sensitive region on both sides of the detector was observed. The model of the diode d epletion volume from the n+ junction side after conduction-type inversion is discussed, and the electric field distribution in the inverted detector is presented. A first evaluation of the strength of the electric field in the undepleted bulk of the detector is proposed

Experimental results on radiation-induced bulk damage effects in float-zone and epitaxial silicon detectors

A comparative study of the radiation hardness of silicon pad detectors, manufactured from Float-Zone and Epitaxial n-type monocrystals and irradiated with protons and neutrons up to a fluence of 3.5 1014 cm-2 is presented. The results are compared in terms of their reverse current, depletion voltage, and charge collection as a function of fluence during irradiation and as a function of time after irradiation

Charge Transport in Non-Irradiated and Irradiated Silicon Diodes

A model describing the transport of charge carriers generated in silicon detectors (standard planar float zone and MESA diodes) by ionizing particles is presented. The current pulse response induced by $\alpha$ and $\beta$ particles in non-irradiated detectors and detectors irradiated up to fluences $\Phi \approx 3 \cdot 10^{14}$ particles/cm$^2$ is reproduced through this model: i) by adding a small n-type region 15 $\mu$m deep on the $p^+$ side for the standard planar float zone detectors at fluences beyond the n to p-type inversion and ii) for the MESA detectors, by considering one dead layer 14 $\mu$m deep (observed experimentally) on each side, and introducing a second (delayed) component. For both types of detectors, the model gives mobilities decreasing linearily up to fluences of about $5 \cdot 10^{13}$ particles/cm$^2$ and converging, beyond, to saturation values of about 1000 cm$^2$/Vs and 455 cm$^2$/Vs for electrons and holes, respectively. At a fluence $\Phi \approx 10^{14}$ particles/cm$^2$, charge collection deficits of about 13\% for $\beta$ particles, 25\% for $\alpha$ particles incident on the front and 35\% for $\alpha$ particles incident on the back of the detector are found for both type of diodes

Study of charge Transport in Silicon Detectors: Non-Irradiated and Irradiated

The electrical characteristics of silicon detectors (standard planar float zone and MESA detectors) as a function of the particle fluence can be extracted by the application of a model describing the transport of charge carriers generated in the detectors by ionizing particles. The current pulse response induced by $\alpha$ and $\beta$ particles in non-irradiated detectors and detectors irradiated up to fluences $\Phi \approx 3 \cdot 10^{14}$ particles/cm$^2$ is reproduced via this model: i) by adding a small n-type region 15 $\mu$m deep on the $p^+$ side for the detectors at fluences beyond the n to p-type inversion and ii) for the MESA detectors, by considering one additional dead layer of 14 $\mu$m (observed experimentally) on each side of the detector, and introducing a second (delayed) component to the current pulse response. For both types of detectors, the model gives mobilities decreasing linearily up to fluences of about $5 \cdot 10^{13}$ particles/cm$^2$ and converging, beyond, to saturation values of about 1050 cm$^2$/Vs and 450 cm$^2$/Vs for electrons and holes, respectively. At a fluence $\Phi \approx 10^{14}$ particles/cm$^2$ (corresponding to about ten years of operation at the CERN-LHC), charge collection deficits of about 14\% for $\beta$ particles, 25\% for $\alpha$ particles incident on the front and 35\% for $\alpha$ particles incident on the back of the detector are found for both type of detectors

Comparison of radiation damage in silicon induced by proton and neutron irradiation

The subject of radiation damage to Si detectors induced by 24-GeV/c protons and nuclear reactor neutrons has been studied. Detectors fabricated on single-crystal silicon enriched with various impurities have been tested. Significant differences in electrically active defects have been found between the various types of material. The results of the study suggest for the first time that the widely used nonionizing energy loss (NIEL) factors are insufficient for normalization of the electrically active damage in case of oxygen- and carbon-enriched silicon detectors. It has been found that a deliberate introduction of impurities into the semiconductor can affect the radiation hardness of silicon detectors. (16 refs)

Study of charge collection and noise in non-irradiated and irradiated silicon detectors

The large collection and noise were studied in non-irradiated and irradiated silicon detectors as a function of temperature (T), shaping time (0) and fluence , up to about 1,2 x 10(14) protons per cm2 for minimum-ionizing electrons yielded by a 106 Ru source. The noise of irradiated detectors is found to be dominted for short shaping times (¾50ns) by a series noise compo- nent, while for longer shaping times (80ns) a parallel noise component (correlated with the reverse current) prevails. For non-irradiated detectors, where the reverse current is three orders of magnetude smaller compared with irradiated detectors, the series noises dominates over the whole range of shaping times investigated (20-150ns). A signal degradation is observed for irradiated detectors. However, the signal ca be distinguished from noise, even after a fluence of about 1.2 x10(14) protons per cm2, at a temperature of 6øC and with a shaping time tipical of rge LHC inter-bunch crossing time (20-30ns). The measurements of the signal as a function of voltage shows that irradiated detectors depleted at 50% of the full depletion voltage can still provide a measurable signal-to-noise ratio