Irradiated Silicon Detectors Operated At Cryogenic Temperature: The Lazarus Effect.

An increasing interest in the behaviour of silicon detectors at cryogenic temperatures has been awakened by the discovery of the so-called Lazarus effect, namely the recovery of Charge Collection Efficiency (CCE) by means of cryogenic cooling. We have measured the CCE of three single diodes previously irradiated with different neutron fluences. The current-voltage characteristic has been measured at 300 K and 77 K, showing that the low temperature operation considerably decreases the steady state current. This is also the case when forward voltage bias is applied, which then becomes a suitable option. At 77 K, in the case of samples irradiated with 510 14 n/cm 2 , the CCE is completely recovered. A third sample irradiated with 210 15 n/cm 2 shows a 60% CCE at 250 V forward bias. a also at Istituto di Cibernetica CNR, Arco Felice, Naples, Italy b also at ETL, Tsukuba, Japan c also at INFN Frascati, Italy Presented at the WSSM1 1999, Torino, Italy, to be published in the P..

Review on the development of cryogenic silicon detectors

In this paper, we report on the performance of heavily irradiated silicon detectors operated at cryogenic temperatures. The results discussed here show that cryogenic operation indeed represents a reliable method to increase the radiation tolerance of standard silicon detectors by more than one order of magnitude. In particular, a 400 mum thick "double- p" silicon detector irradiated up to 1 x 10(15) n/cm(2) delivers a mip signal of about 27 000 electrons when operated at 130 K and 500 V bias. The position resolution of an irradiated microstrip detector, and "in situ" irradiation of a pad detector during operation in the cold are also discussed

Silicon detectors irradiated "in situ" at cryogenic temperatures

Though several studies have proved the radiation tolerance of silicon detectors at cryogenic temperatures, following room temperature irradiation, no previous investigation has studied the behaviour of detectors irradiated "in situ" at low temperatures. In this work, effects of irradiation of 450 GeV protons at 83 K will be presented, showing that after a dose of 1.2 x 10(15) p cm(-2) a charge collection efficiency (CCE) of 55% is reached at 200 V before the annealing. The same results were found at the end of the irradiation. after the sample has spent more then one year at room temperature, This shows that the CCE recovery by low temperature operation is not affected by the temperature of irradiation and by the reverse annealing

Optimization of electric field distribution by free carrier injection in silicon detectors operated at low temperatures

We present a study of the modeling of the electric field distribution, which is controlled by injection and trapping of nonequilibrium carriers, in Si detectors irradiated by high neutron fluences. An analytical calculation of the electric field distribution in detectors irradiated by neutrons up to fluences of 1 . 10(14) to 5 . 10(15) cm(-2) shows the possibility of reducing the full depletion voltage at low temperatures via hole injection. For this calculation, we use the detector operating parameters and equivalent neutron fluences expected for Large Hadron Collider experiments. The results of the calculation are in good qualitative agreement with published experimental data, lending strong support for the model and for an earlier proposal of electric field manipulation by free carrier injection

Charge collection efficiency of an irradiated cryogenic double- p silicon detector

We present results on the measurement of the charge collection efficiency of a p(+) /n/p(+) silicon detector irradiated to 1 x 10(15) n/cm(2), Operated in the temperature range between 80 and 200 K. For comparison, measurements obtained with a standard silicon diode (p(+) /n/n(+)), irradiated to the same fluence, are also presented. Both detectors show a dramatic increase of the CCE when operated at temperatures around 130 K. The double-p detector shows a higher CCE regardless of the applied bias and temperature, besides being symmetric with respect to the polarity of the bias voltage

Charge collection efficiency of irradiated silicon detector operated at cryogenic temperatures

The charge collection efficiency (CCE) of heavily irradiated silicon diode detectors was investigated at temperatures between 77 and 200 K. The CCE was found to depend on the radiation dose, bias voltage value and history, temperature, and bias current generated by light. The detector irradiated to the highest fluence 2 x 10(15) n/cm(2) yields a MIP signal of at least 15000 e(-) both at 250 V forward bias voltage, and at 250 V reverse bias voltage in the presence of a light-generated current. The "Lazarus effect" was thus shown to extend to fluences at least ten times higher than was previously studied

Radiation hard position-sensitive cryogenic silicon detectors: the Lazarus effect

The discovery of the so-called Lazarus effect, namely the recovery of the charge collection efficiency (CCE) of irradiated silicon detectors by means of cryogenic cooling has entailed an increasing interest in the behavior of silicon detectors at cryogenic temperatures. We have measured the CCE of a silicon p-i-n diode detector previously irradiated with an equivalent fluence of 1 x 10(15) n/cm(2) neutrons of 1 MeV energy. The charge collection efficiency has been measured at 77 ii;. showing that the low-temperature operation considerably decreases the bias current. This is also the case when forward voltage bias is applied, which then becomes a suitable option. In this condition, the sample shows a charge collection efficiency in excess of 65% at 250 V corresponding to a most probable signal for a minimum ionizing particle of 21000e(-)

Radiation hardness of cryogenic silicon detectors

We shall review test results which show that silicon detectors can withstand at 130 K temperature a fluence of 2 x 10(15)cm(- 2) of 1 MeV neutrons, which is about 10 times higher than the fluence tolerated by the best detectors operated close to room temperature. The tests were carried out on simple pad devices and on microstrip detectors of different types. The devices were irradiated at room temperature using reactor neutrons, and in situ at low temperatures using high-energy protons and lead ions. No substantial difference was observed between samples irradiated at low temperature and those irradiated at room temperature. after beneficial annealing. The design of low-mass modules for low-temperature trackers is discussed briefly, together with the cooling circuits for small and large systems