Cadmium zinc telluride (CZT) is one of the most promising materials for production of large-volume gamma-ray spectrometers and imaging arrays operable at room temperature. The performance of CZT devices, the global capacity for growth of detector-grade crystals, and the size of the commercial market have progressed steadily over the past ten years. Because of deficiencies in the quality of the material, high-resolution CZT spectrometers are still limited to relatively small dimensions (< 2-3 cm³), which makes them inefficient at detecting high photon energies and somewhat ineffective for weak radiation signals except in near proximity. The detectors are very attractive for a much broader range of applications; however, increases in their efficiency are needed without sacrificing the ability to spectrally resolve gamma energies. Achieving the goal of low-cost efficient detectors requires progress in the following areas: growth of large uniform single crystals, reductions in carrier trapping, increases in electrical resistivity, and improved device fabrication procedures. Despite the current material constraints, several types of electron-transport-only detectors have been developed: pixel, coplanar-grid, cross-strip, drift-strip, orthogonal coplanar strip, and virtual Frisch-grid, some of which are now addressing important applications. These devices have many similar operational features and common problems limiting their performance. This talk summarizes the material factors limiting performance of CZT detectors and the common constraints on detector designs: bulk and surface leakage currents, surface effects, properties of Schottky contacts, surface interfacial layers, charge sharing and loss in multi-electrode devices, charge transport non-uniformities, and fluctuations in the pulse height for long-drift devices. We also describe new capabilities at Brookhaven for CZT device characterization and recent progress to characterize the material and devices.

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