L. Vasanelli

PbI2 as Nuclear Particle Detector

PbI2 detectors fabricated starting from samples either grown from the melt by the Bridgman method either from the vapour by the iodine assisted chemical transport method, have been tested for nuclear applications and compared each other in this respect. Values of (mobility) × (trapping times) product, ¿¿+, measured both for electrons and holes turn out to be one or two orders of magnitude larger than reported previously and they are better for vapour-grown samples than for melt-grown ones. Moreover, dark currents seem to be one or two orders of magnitude lower for samples grown from the vapour-phase. The indication is obviously that, at least at this early stages, the growth by the chemical transport seems to be superior to the Bridgman method for obtaining detector quality crystals. Finally, the main features of this material as nuclear detector are discussed.

Hall effect in n-type GaS

Abstract Hall effect measurements have been performed for the first time on n -type GaS single crystals, grown buy the Bridgam-Stockbarger method. Electrical properties are dominated by a donor centre at 0.52 eV, with a concentration of 2.3 × 10 16 cm –3 . The conduction band density-of-states effective mass has been estimated to be 1.3 m e . The low temperature conduction is compatible with a hopping process with an activation energy of 0.15 eV.

GaSe as nuclear particle detector

Abstract GaSe grown by means of chemical transport and of the Bridgman method has been tested with 14Am α-particle for application as nuclear detector. Collection efficiency ranges from 5–40%, corresponding to μτ+ products between 10−7 and 1.5×10−6 cm2V−1. Energy resolution can be as low as 6%. The main handicaps to better performances seem to be due to sample inhomogeneities and injecting contacts; improvements are in the range of present technology. Particular applications of this type of detector are also suggested.

ZnO/CdTe heterojunctions prepared by r.f. sputtering

Abstract ZnO/CdTe heterojunctions were prepared by r.f. sputtering of ZnO films onto p-type CdTe single crystals. The ZnO deposition was carried out using a ZnO target and an Ar-H2 mixture as the sputtering gas. The ZnO films obtained under these conditions show a very good optical transmission (about 90%) between 0.4 and 0.8 μm and a low resistivity. The electrical properties of the ZnO/CdTe heterojunctions were studied by means of current-voltage (I-V) and capacitance-voltage (C-V) measurements carried out at different temperatures. The dark I-V characteristics show that a multistep tunnelling mechanism controls the transport of charge carriers across the junction. The presence of interface states was shown to play an important role in the electrical properties of the junction. Tentative measurements of the solar energy conversion efficiency gave a value of about 3.5% without any attempt at optimization of the cell parameters.

A particular application of GaSe semiconductor detectors in the neutrino experiment at CERN

Abstract A particular application of GaSe semiconductor detectors for monitoring a high energy muon beam, was investigated during the neutrino experiment at CERN. The performances of GaSe detectors were compared with those of some silicon detectors currently used in this neutrino experiment. Linearity and stability tests indicate that the performances of GaSe detectors are comparable with those of silicon for this particular application. Some other tests on these detectors demonstrate that they are very resistant to radiation damage and aging effects. In conclusion, GaSe detectors look promising for monitoring muon beams, and their low cost can allow the realization of arrangements of many detectors to control continuously the intensity and the spatial symmetry of muon beam.

Preparation of transparent conducting zinc oxide films by reactive sputtering

Abstract Transparent conducting zinc oxide films have been prepared by reactive sputtering in an Ar/H2 mixture. The optical and electrical properties of the films are presented and discussed. The effects of different post-deposition thermal treatments have been also investigated. ZnO/CdTe heterojunctions have been prepared by sputtering ZnO films on p-CdTe single crystals. The highest photovoltaic conversion efficiency of the solar cells obtained was 6.8%.

Space-charge limited currents in n-GaSe crystals

Abstract Measurements performed on n -GaSe crystals by means of the space-charge limited current method indicate the presence of two deep electron traps, at 0.62 and 0.68 eV below the conduction band, with an energy width of 0.13 eV and a concentration of about 10 13 cm −3 . Various tests confirm that single carrier (electrons) injection in a space-charge regime is the dominant mechanism in measured I–V curves. The connection between traps and defective structure of n -GaSe is discussed.

The Use of GaSe Semiconductor Detectors for Monitoring High Energy Muon Beams

GaSe semiconductor detectors have been successfully tested during one year for monitoring muon beams in the GeV range in the neutrino experiment at CERN. Their performances are comparable with those of commercial Si surface barrier detectors for this particular application. Crystal growth, detec tor fabrication and characterization are briefly described. Various advantages (cost, ruggedness, resistance to radiation damage, manufacturing simplicity, etc.) are discussed.

Electrical properties of ZnO/CdTe heterojunctions

Abstract ZnO/CdTe heterojunctions have been prepared by RF sputtering of ZnO films on CdTe single crystals. The sputtering has been performed in an Ar/10%H2 mixture, in order to deposit low resistivity transparent ZnO films. The electrical properties of the as-deposited junctions are quite poor, but they can be improved by a post-deposition heat treatment in a H2 atmosphere. Current-voltage characteristics have been measured at different temperatures. They clearly show that current transport is dominated by a multistep tunneling/recombination mechanism, for both forward and reverse bias. The main features of junctions, prepared under different experimental conditions, are presented and discussed.

Hall effect in GaTe single crystals

Abstract Hall effect measurements have been carried out over the temperature range 77–500K on p -type GaTe single crystals, grown from the melt. The results indicate that scattering by homopolar optical phonons polarized normally to the layers is largely dominant in GaTe. From the analysis of Hall mobility data, carried out according to the Schmids model, a phonon energy h ω = 9.8 meV and the product between the coupling constant and the hole conduction mass along the layers g 2 m h ⊥ = v .205 me has been found Finally, an acceptor center, lying at 138 meV from the valence band, displays an hydrogen-like behaviour, with its energy dependent from concentration according to the theory.