R. Murri

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.

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.

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.

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.

Anisotropy of the photomagnetoelectric effect in mercury iodide

Abstract Measurements of the photomagnetoelectric (PME) effect and of photoconductivity (PC) on mercury iodide single crystals have been carried out with the light incident along or perpendicular to the c-axis. The comparison of the short-circuit PME current and PC current in the two cases, allows to estimate for the first time the hole mobility along the layers. The dependence of the PME effect on the intensity of light, shows the presence of trapping.

Influence of iodine doping on the electrical properties of GaSe

Abstract Systematic measurements of resistivity and mobility at room temperature have been carried out on GaSe samples, doped with different iodine concentrations, in order to investigate the influence of iodine doping on the electrical properties of GaSe. To this purpose a series of GaSe single crystals have been grown by the iodine vapour transport technique in the same experimental conditions, with different iodine concentrations in the growth ampoule. By means of the Van der Pauw method, the electrical characteristics of some samples have been measured for each growth run, together with the behaviour of resistivity as a function of temperature. The results clearly indicate that GaSe, which undoped has a p-type conductivity, becomes a n-type semiconductor with the iodine introduction. The room temperature resistivity decrease and the carrier concentration increase at larger amounts of iodine. The conductivity is controlled by some donor levels lying at about 0.32, 0.5 and 0.62 eV from the conduction band, as it has been evidenced by ϱ(T) and TSC measurements.

The Photomagnetoelectric Effect in Mercury Iodide

In order to investigate the transport properties of mercury iodide, measurements of photomagnetoelectric (PME) effect and photoconductivity (PC) have been carried out. The experimental results show the presence of trapping phenomena and a strong dependence of carrier lifetimes on the light injection level. The obtained values of the lifetimes are in the range 10-7-10-6 s.

Photomagnetoelectric effect in n-GaSe single crystal in presence of traps

Abstract The anisotropy of the phenomenological transport parameters for the layer semiconductors is taken into account for the photomagnetoelectric (PME) effect. Moreover, a model has been carried out which, in the case of small signal levels, takes also into account the presence of traps and their recombination kinetics, to explain the observed spectral distributions of the short circuit PME current and of the photoconductivity. An application to GaSe is then shown, and a best fit method, applied to the experimental spectra of the short-circuit current and of the photoconductivity, allows one to determine some phenomenological parameters as: carrier lifetimes, diffusion length, surface recombination velocity and trap energy levels.