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Raulo A.,EURORAD | Hennard G.,EURORAD | Sowinska M.,EURORAD | James R.B.,Brookhaven National Laboratory | And 4 more authors.
IEEE Transactions on Nuclear Science | Year: 2013

The various crystal growing methods (Low Pressure Bridgman, High Pressure Bridgman, Horizontal Bridgman, Physical Vapor Transport, Travelling Heater Method - THM) and the subsequent bulk and surface treatments can greatly affect the performances of CdTe as well as CdZnTe based X-ray detectors. For this investigation THM was chosen as a low temperature growth process where the crystals have relatively low number of defects and less impurity incorporation from the crucible. Surface (i.e., electrode and electrode-bulk material interface) characteristics have been already investigated , , aiming at understanding the effects of annealing on the electrode deposition. Here bulk effects, including an analysis of the Te inclusion distribution, on CdTe wafers obtained starting from as-grown or subsequently annealed standard or large area ingots have been investigated by IR imaging, resistivity and electron mobility mappings as well as spectroscopic characterization. The results of these measurements are presented and correlated with the detector performances of hundreds of samples. The main observed effects of the annealing are a reduction of the large size ({>} 10\ \mum) Te inclusions and a peaking of the resistivity and electron mu-tau products, though in this last case around worse average values, over the entire wafers, that lead to a significant reduction of the spread in the electron transit times, and at the end to better spectroscopic performances. © 1963-2012 IEEE.

Sowinska M.,EURORAD | Simon H.,EURORAD | Raulo A.,EURORAD | Mycielski A.,Istiute of Physics | And 3 more authors.
IEEE Nuclear Science Symposium Conference Record | Year: 2012

Despite intensive research for the improvement of the quality of II-VI crystals, until now no clear method permits to determine quickly the performance of final detector, directly on the as-grown crystal or on the wafers. This situation induces excess cost, which hinders the development of detectors based on these binary and ternary semiconductors. © 2011 IEEE.

Raulo A.,EURORAD | Sowinska M.,EURORAD | Hennard G.,EURORAD | Campajola L.,University of Naples Federico II | And 3 more authors.
IEEE Transactions on Nuclear Science | Year: 2012

X-and Gamma-Ray spectroscopy measurements have been performed on differently prepared CdTe samples (as-grown or annealed, different surface treatments, etc.) with Pt electrodes deposited by electroless technique in order to extract the typical figures of merit of the material and the detectors. Moreover, Rutherford Backscattering Spectrometry (RBS) using 8 MeV 7Li +++ ions and X-Ray Fluorescence (XRF) using a Pd-anode X-Ray generator were performed to characterize the crystal surface as well as the semiconductor-electrode interface. The thickness, the stoichiometry and the concentration profiles of platinum, cadmium and tellurium present at the surface layers were determined. The distribution of Cd deficiency at the interface layers was profiled using simulations and showed complex profiles in the samples, that can greatly affect the electrical quality of the detectors. In addition, resistivity and mu-tau product mapping and electrical measurements have been performed for material characterization. The aim of this work is to understand and improve the structure of the material-electrode interface; in particular, to understand the effect of the annealing process on the fabrication of the contacts and, at the end, on the performances of the detectors. For this reason a large number of detectors have been produced applying various chemical surface treatments on as-grown and annealed material, in order to determine the best routine way to fabricate high-quality X-and Gamma-ray detectors to be used both as large size planar detectors and as elements of imaging systems in medical or industrial applications. © 1963-2012 IEEE.

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