C. Manfredotti

Electrical properties and performances of natural diamond nuclear radiation detectors

Abstract Hole and electron drift velocities and mean free drift time have been measured with a time-of-flight technique as functions of electric field in crystals of natural diamond. The performances of diamond nuclear radiation detectors have been investigated using alpha and beta particles. An energy for electron-hole pair creation of 13.19 eV has been determined for alpha particles in the 5–6 MeV energy range. Spectral lines of alpha particles within this energy range have shown a resolution of 82 keV at room temperature.

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.

Electron trapping levels in cadmium selenide single crystals

Measurements of space‐charge‐limited currents have been performed on CdSe single crystals between 77 and 400 °K. Four groups of electron trapping levels have been found at 0.64, 0.49, 0.35, and 0.167 eV, with densities ranging from 5 × 1010 to 1013 cm−3. A check of the results with photocurrent vs light intensity and thermally stimulated currents measurements is presented. The origin and the nature of these centers is discussed and correlated with mobility values measured in the crystals investigated. Finally, contacts and geometry considerations are reported.

Hole centers in GaSe

A systematic investigation of hole centers acting in p‐GaSe single crystals has been carried out by means of the following methods: (i) dark conductivity measurements as a function of temperature; (ii) space‐charge‐limited‐current measurements extended from 77 to 300 °K; (iii) thermally stimulated‐current measurements as a function of temperature. A series of hole centers has been found with energy depths ranging from 26 to 400 meV from the valence band and densities of about 1013 cm−3. A complete summary of the energy levels present in the forbidden gap of GaSe up to 600 meV from the valence band is given. A comparison is made between the results of this work, previously reported data, results obtained by Hall‐effect versus temperature measurements, and data quoted by other authors. Finally, the origin and nature of all the hole centers are discussed, taking into account their possible connections with the defective structure of GaSe.A systematic investigation of hole centers acting in p‐GaSe single crystals has been carried out by means of the following methods: (i) dark conductivity measurements as a function of temperature; (ii) space‐charge‐limited‐current measurements extended from 77 to 300 °K; (iii) thermally stimulated‐current measurements as a function of temperature. A series of hole centers has been found with energy depths ranging from 26 to 400 meV from the valence band and densities of about 1013 cm−3. A complete summary of the energy levels present in the forbidden gap of GaSe up to 600 meV from the valence band is given. A comparison is made between the results of this work, previously reported data, results obtained by Hall‐effect versus temperature measurements, and data quoted by other authors. Finally, the origin and nature of all the hole centers are discussed, taking into account their possible connections with the defective structure of GaSe.

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.

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.

Electron traps in GaS

Abstract Measurements performed on n-GaS by means of the space-charge limited current method indicate the presence of a deep trap for electrons, at 0.57 eV from the conduction band and with a density of about 2.3 × 1013cm−3. Another deeper trap at 0.63 eV and with a density of 6 × 1012cm−3 is probably also present. The results seem to confirm the validity of a new direct method of analysis. Traps are tentatively attributed to compensated sulphur vacancies.

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.