PACS 71.55. Gs, 72.20.Jv, 72.80.Ey, 81.05.Dz, 85.60.Gz Good detection efficiency and high energy-resolution make Cadmium Zinc Telluride (CdZnTe) and Cadmium Telluride (CdTe) detectors attractive in many room temperature X-ray and gamma-ray detection applications such as medical and industrial imaging, industrial gauging and non-destructive testing, security and monitoring, nuclear safeguards and non-proliferation, and astrophysics. Advancement of the crystal growth and device fabrication technologies and the reduction of bulk, interface and surface defects in the devices are crucial for the widespread practical deployment of Cd 1-x Zn x Te-based detector technology. Here we review the effects of bulk, interface and surface defects on charge transport, charge transport uniformity and device performance and the progress in the crystal growth and device fabrication technologies aiming at reducing the concentration of harmful defects and improving Cd 1-x Zn x Te detector performance.1 Introduction Semi-insulating CdTe and CdZnTe have long been known to have great potential in room-temperature X-ray and gamma ray semiconductor detector applications [1,2]. The high atomic number and density of these compounds provide strong absorption and high detection efficiency of highenergy photons. The wide band gap of the materials allows the fabrication of highly resistive devices enabling large depletion depths and low leakage currents, when the material is brought into the semiinsulating state with electrical compensation techniques. The moderately high mobility and lifetime of charge carriers (particularly electrons) allow good charge transport in devices depleted to many mm or even cm thickness. The full potential of these compounds for high-energy photon detection applications, however, was not exploited for many decades due to the limited commercial availability of high-quality crystals. This situation has changed dramatically during the mid nineties with the emergence of few small companies committed to the advancement and commercialisation of the Cd 1-x Zn x Te based radiation detector technology. Today, Cd 1-x Zn x Te radiation detectors and detection systems find applications in industrial monitoring, gauging and imaging, medical imaging, nuclear safeguards and nonproliferation, transportation security and safety, as well as in a range of scientific applications.In this paper we will give a short review of the status of Cd 1-x Zn x Te-based X-ray and gamma ray radiation detector technology. First we will discuss the material requirements posed by the design criteria of room temperature semiconductor detectors. We will continue with the crystal growth and device fabrication challenges faced in the manufacturing of high-quality Cd 1-x Zn x Te radiation detectors.

In this paper, we theoretically investigate the mechanism of polarization in wide-bandgap semiconductor radiation detectors under high-flux x-ray irradiation. Our general mathematical model of the defect structure within the bandgap is a system of balance laws based on carrier transport and defect transition rates, coupled together with the Poisson equation for the electric potential. The dynamical system is self-consistently evolved in time using a high-resolution wave propagation numerical algorithm. Through simulation, we identify and present a sequence of dynamics that determines a critical flux of photons above which polarization effects dominate. Using the experience gained through numerical simulation of the full set of equations, we derive a reduced system of conservation laws that describe the dominant dynamics. A multiple scale perturbation analysis of the reduced system is shown to yield an analytical dependence of the maximum sustainable flux on key material, detector, and operating parameters. The predicted dependencies are validated for 16ϫ 16 pixel CdZnTe monolithic detector arrays subjected to a high-flux 120 kVp x-ray source.

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