[en] In this work an easy method for determining the cadmium and tellurium excess in CdTe samples is presented. The technique showed an accuracy of better than 0.001 at.%, which is two orders of magnitude better than was previously reported. The technique is based on a detailed analysis of Cd and Te₂ partial vapour pressures in equilibrium with CdTe samples at high temperatures. The partial pressures are determined by separately measuring the optical absorption of the vapours at the wavelengths of a He-Cd laser source (326 and 442 nm). The results of measurements of both Cd and Te-rich samples will be presented

[en] Nominally undoped CdTe crystals are grown by both vapour phase and Bridgman technique. The stoichiometry of the feed charge was adjusted in order to obtain n-type, p-type and high resistivity crystals. The stoichiometry of CdTe samples is studied by means of a detailed analysis of the temperature dependence of the equilibrium partial pressures of Cd and Te₂ vapours. A strong evidence of a correlation of the stoichiometry and the resistivity of the samples has been found. This suggests that a stoichiometry related defect plays an important role in the compensation mechanism of the nominally undoped crystals. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] The description of SnO₂ nanowires growth procedures are getting more and more frequent in the current literature. However, studies on the growth mechanisms are still lacking. In particular, no investigation has been reported on the growth process when the growth mechanisms are not based, as in the case of whiskers, on vapour-liquid-solid (VLS) transitions. In this paper, a new procedure is reported by the authors for growing SnO₂ nanowires, based on the presence of liquid-tin droplets on the substrate. The Sn vapour pressure developed by these droplets, which find themselves very close to the growing tip of the wire, gives rise to a sufficiently high supersaturation to enable the fast growth rate usually observed. The principal features and results of this new procedure, as well as possible growth mechanisms, are also discussed

[en] In this work, we report on the structural analyses of undoped CdTe samples grown by the vapor phase and the Bridgman methods. Different techniques were used for determining the structural defects: wet etching, high resolution X-ray diffraction, double crystal X-ray topography and monochromatic SEM-cathodoluminescence mapping. The density and the nature of the structural defects were found to be correlated to the stoichiometry of the samples, as determined by a detailed analysis of the temperature dependence of the partial pressure of the vapors in equilibrium with the solid. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] This work focuses on the influence of stoichiometry deviation (Cd/Te excess in the crystal) on the type and density of crystalline defects. In particular, we report a study on the evaluation of extended defects and precipitates, carried out by specific preferential etching, high-resolution x-ray diffraction, double-crystal x-ray topography and cathodoluminescence (CL) analyses. A remarkable difference between the crystals grown from the vapour phase and from the melt has been found. Dislocations were found to arrange in cellular structures 2-300 μm in diameter while precipitates were homogeneously distributed on the growth plane. The CL spectra show an intense near-band-edge emission through the whole range of temperatures and two large emission bands centred at 1.2 and 1.4 eV. It has been observed that the luminescence intensity of the 1.4 eV band increases close to crystal defects and simultaneously the near-band-edge intensity decreases. The disappearance of this emission both in the CL spectra and in the CL images on increasing the temperature up to 300 K suggests a donor-acceptor pair nature for the transition involved

[en] The Large High Altitude Air Shower Observatory (LHAASO) is a multi-component experiment to study cosmic ray physics, which is under construction near Mt. Haizishan (4410 m a.s.l.) in Southwest China. The 78,000 m² Water Cherenkov Detector Array (WCDA), which is one of the main components of the LHAASO, will be able to survey the gamma-ray sky continuously in the energy range from 100 GeV to PeV. The precision of the time measurement in the detector cells of WCDA determines the sensitivity to the direction of gamma ray sources, necessitating a hardware calibration system to be deployed in the WCDA. Effects such as environment temperature variations will introduce time offsets between detector cells. In order to calibrate the time offset, a method using high-statistics low-energy cosmic rays has been developed. The detector cells are divided into clusters of 6×6 cells which are calibrated locally. This paper then describes the technique combining all the detector cells and demonstrates that the performance meets the requirements. The high-statistics of low-energy cosmic rays makes it possible to calibrate the detector in real time.

[en] The Water Cherenkov Detector Array (WCDA), which is one of the main components of the Large High Altitude Air Shower Observatory (LHAASO), functions in surveying the northern sky for high-energy gamma ray sources at the energy range around of 100 GeV–30 TeV. The precision of the time measurement for shower particles hitting every detector in the array is directly associated with the detection sensitivity for the sources. The calibration precision of the time offsets among the detector cells should be less than 0.1 ns to obtain less than 0.1^o pointing error of the detector to any point source. In this regard, 'cross calibration' is employed for the detector array, with 180 bundles of fiber systems guiding the lights of LEDs to each PMT. A test bench comprising fast PMTs and an one-dimensional slide platform is set up in the laboratory to test the fiber bundles. The test bench and the test procedure is described in this paper, and the test results are presented.

[en] The effect of DS(L) (Diluited Sirtl with or without Light) solution on CadmiumTelluride crystals has been studied in comparison with the actions due to Inoue and Nakagawa etching solutions. The use of chemical etching to reveal extended defects is a fast and useful technique for characterizing the crystals with the aim of improving the growth technology and better devices performance. In fact it is well known that extensive defects in CdTe crystals have a relevant role on the material properties and finally on the devices performance. DSL solution previously used on Si, GaAs and InP, here has been used for the first time on CdTe crystals. The etching solutions have been used to characterize crystals with two different characteristics: the first group shows high electrical resistivity and close to stoichiometry composition, the second one shows low resistivity behaviour and large Te deviation. We report here the preliminary results of the characterization of these crystals with the DSL etching. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] A wide field of view Cherenkov/fluorescence telescope array is one of the main components of the Large High Altitude Air Shower Observatory project. To serve as Cherenkov and fluorescence detectors, a flexible and mobile design is adopted for easy reconfiguring of the telescope array. Two prototype telescopes have been constructed and successfully run at the site of the ARGO-YBJ experiment in Tibet. The features and performance of the telescopes are presented.

[en] The Large High Altitude Air Shower Observatory (LHAASO) is planned to be built at Daocheng, Sichuan Province, China. The water Cherenkov detector array (WCDA), with an area of 78,000 m"2 and capacity of 350,000 tons of purified water, is one of the major components of the LHAASO project. A 9-cell detector prototype array has been built at the Yangbajing site, Tibet, China to comprehensively understand the water Cherenkov technique and investigate the engineering issues of WCDA. In this paper, the rate and charge distribution of single-channel signals are evaluated using a full detail Monte Carlo simulation. The results are discussed and compared with the results obtained with prototype array.