A. Seidman

Some physical properties of ZnO sputtered films

Abstract The secondary electron emission (SEE) yield δ of ZnO films was investigated. The films were deposited in an r.f. sputtering system using the r.f. power W , the argon pressure p , the O 2 partial pressure p O 2 and the substrate temperature T s as parameters. Complementary measurements of the electrical resistivity ϱ and the optical absorption α were performed. The ratio x of oxygen to zinc is an essential factor which determines the values of δ, ϱ and α for the ZnO films. Auger analyses showed that excess (overstoichiometric, x =1) oxygen is present in ZnO films obtained at room temperature. For x =1 the values of ϱ, the maximum SEE yield δ m and the energy band gap E g (determined from α) were found to be higher than those for stoichiometric ZnO (obtained at T s 200 °C). The highest values of ϱ (10 4 Ω m), δ m (4.4) and E g (3.44 eV) were obtained for films with x = 1.7.

Electromagnetic shower development in uranium and tungsten: A comparison of data from a silicon sampling calorimeter

Abstract Longitudinal electromagnetic shower development has been studied in uranium and tungsten using a sandwich calorimeter with silicon as the active medium. Data were taken with incoming electron energies of 2, 4 and 6 GeV. The silicon detectors were operated with depletion layers of both 200 and 70 μm. The energy resolution of the calorimeter was reduced by less than 10–15% when the detectors had depleted layer widths of 70 μm.

The local hardening effect on electromagnetic showers. A way for signal equalization in Si/high-Z hadron calorimeters

Abstract The condition for obtaining the linear response of a calorimeter to hadronic showers and an energy resolution improving as the incident energy increases is the equalization between the electromagnetic and the hadronic signals. This equalization is obtained within a new approach exploiting a local hardening effect that is realized by inserting low-Z absorbers next to the silicon readout detectors. In this way, the calorimeter response to the electromagnetic component of the hadronic shower is reduced. A systematic investigation of the visible energy response for electromagnetic showers in Si/U and Si/W calorimeters has been carried out for incoming electron energies of 2, 4, and 6 GeV. The insertion of low-Z material (G10 plates) in front or at the rear of the silicon detectors allows a fine tuning of the calorimeter response.

Silicon sampling hadronic calorimetry: A tool for experiments at the next generation of colliders

Abstract The SICAPO Collaboration project to build a perfectly compensating hadron calorimeter using silicon as the active medium, is described. The insertion of low-Z material (G10 plates) in front or at the rear of the silicon detectors allows fine tuning of the calorimeter response to electromagnetic showers. This is a new approach to obtaining compensation. The tuning can be exploited to obtain e/π = 1 (compensation condition). The expected performance ranks this calorimeter among the best candidates to face the severe constraints requested by the next generation of colliders.

Experimental results from a sandwich calorimeter using U absorbers and 0.25 m2 of Si active area

Abstract The electromagnetic section of a hadronic calorimeter, consisting of uranium absorbers and of silicon sampling units with an active area of 0.25 m2, was investigated. The overall performance of the silicon detectors and especially developed associated electronics, seems to be stable and reliable. During a four-week run at the t9, CERN-PS (Proton Synchrotron) electron beam (energies of 2 to 6 GeV), no variation of energy calibration of the calorimeter was observed. The energy resolution for electromagnetic showers was found to be about 19.8% ( τ E ) , where E is the energy of the incoming electron and τ is the number of radiation lengths of passive material interspaced between two active samplers, for a calorimeter depth of 15.6 X0 (radiation lengths), with Si samplers depleted to 200 μm. The fiberglass supports of the silicon mosaics cause a reduction of energy response to electromagnetic showers. It can be exploited to equalize the response of a Si/U hadronic calorimeter to incoming electrons and hadrons.

Effect on charge collection and structure of n-type silicon detectors irradiated with large fluences of fast neutrons

Abstract Float-Zone (FZ) silicon detectors have been irradiated with large fast neutrons fluences (up to 1014 n/cm2). The charge collection efficiency (eff) dependence on the reverse bias voltage (V) and on the fluence (Φ) have been investigated. The charge collection dependence on V indicates that, after large neutron irradiation, the relation between charge carrier concentration and full depletion voltage does not obey any longer the standard equation for an unsymmetrical step junction. The charge collection efficiency is found to have a logarithmic dependence on Φ.

Evidence for the compensation condition in Si/U hadronic calorimetry by the local hardening effect

Abstract In a hadronic calorimeter with silicon readout, a combination of thin plates oflow- Z andhigh- Z materials used as absorbers enables the reduction of the calorimeter response to the electromagnetic component of the incoming hadronic showers (the “local hardening effect”). As a result, a ratio varying from e/π> 1 toe/π>is obtained as a function of thelow- Z material thickness, demonstrating the possibility of achieving the compensation condition(e/π= 1)by exploiting the local hardening effect.

Silicon sampling calorimetry

Abstract A review of experimental studies carried out by the SICAPO collaboration at CERN on Si/W and Si/U sandwich calorimeters is presented. Results on the response of sensed energy versus incoming electron energy and depleted layer width, of the longitudinal and lateral development of electromagnetic showers and of the energy resolution are given and compared with data from Hamburg (Si/Pb) and Tokyo (Si/Pb and Si/W) calorimeters. The performance of the electromagnetic section of a large Si/U hadronic calorimeter is also described.

Electroless and sputtered silver-tungsten thin films for microelectronics applications

Thin silver-tungsten (Ag-W) films have been deposited on Si and SiO2 substrates by electroless (El) and ion-beam sputtering (IBS) methods and their morphology was studied by optical and atomic force microscopy. Adding tungsten into the silver film significantly improved its corrosion stability, electrical, optical and mechanical properties. TEM microstructure investigation shown that W is introduced into Ag film in the form of WO3. In this paper we compare the resistance, reflectance and morphology, as determined by atomic force microscopy, of Ag-W films deposited by El and IBS methods for microelectronics application. Finally we present results of the Ag-W films study as barrier for silver metallization by MOS capacitors measurements. The capacitors exhibited almost ideal C-V high frequency characteristics and flat band voltage near to zero. The generation life-time (τ) and the recombination surface velocity (s) were of the same order of those for similar structures with Cu, Co and Al metallization. Those results indicate that Ag-W layers are MOS technology compatible and can be used in microelectronics as a new interconnect and metallization material.

Current-voltage and impedance characteristics of neutron irradiated silicon detectors at fluences up to 1016 n/cm2

The effect of neutron irradiation at very high fluences up to ƒ ∼ 1016n/cm2 on the rectifying properties of silicon high energy detectors was studied. It was shown that at critical fluences, ƒcl ∼ 1012–1013n/cm2 and ƒc2 ∼ 1.2 × 1014n/cm2, abrupt changes of the forward current, rectifying factor and other parameters, appear. Measurements of impedance (Z) as a function of frequency (f) show that, after strong irradiation, the real and imaginary part of Z and losses depend on f. They may be related to a decrease of lifetime of free carriers, due to traps caused by high irradiation.