Spectroscopic evaluation of n-type CdZnTe gamma-ray spectrometers

This work focuses on the evaluation of the spectroscopic performance of n-t ype CdZnTe gamma-ray spectrometers, grown by a modified horizontal Bridgman Technique developed at IMARAD Imaging Systems Ltd. Two types of devices ar e studied: (i) detector arrays grown and produced by IMARAD and employing o hmic indium contacts and (ii) detectors and arrays fabricated at Technion i n crystals provided by IMARAD, employing different types of contacts. Alpha particle spectroscopy as well as gamma-ray spectroscopy is used to evaluat e and characterize the energy resolution of gamma-ray spectrometers fabrica ted on n-type CdZnTe grown by a modified horizontal Bridgman and doped with indium. The electron and hole mobility lifetime products of the n-type CdZ nTe material grown by IMARAD are estimated by measuring the dependence of c harge collection efficiency upon the bias voltage, using a calibrated multi channel analyzer. The measured results indicate that the average electron a nd hole mobility-lifetime products are, respectively, of the order of mu(n) tau(n) = (1-2) . 10(-3) cm(2)/V and mu(p)tau(p) = 6.10(-6) cm(2)/V. The mea sured energy resolution of 122 keV photons is -(5-6)% when the source is no t collimated and is reduced to -4.5% when the source is collimated. These r esults are obtained with ohmic cathode as well as with a rectifying cathode . A statistical model for the calculation of the pulse height spectra as a function of photon energy, electron and hole mobility-lifetime products and applied electric field, which has been recently reported in Applied Physic al Letters, is used to determine the role of incomplete charge collection i n the spectral performance of the n-type CdZnTe spectrometers. The comparis on between the measured and modeled results indicates that the dark noise, cross talk and non-uniformity are the main limiting factors of the spectral performance of the n-type spectrometers rather than incomplete charge coll ection. The good spectroscopic performance of the arrays under study is att ributed to an adequate hole mobility lifetime for the geometry of the pixil ated arrays. The study indicates that the n-type CdZnTe spectrometers are u seful for a wide range of imaging applications.