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Low dislocation density, high-purity, and low inclusion concentration Cd0.9Zn0.1Te (CZT) and CdTe crystals were grown by a vertical Bridgman technique using in-house zone refined precursors. The grown crystals were sequentially processed using optimized chemo-mechanical processes to fabricate planar and Frisch collar detectors. Infrared transmission and scanning electron microscopy studies have shown that EIC grown CZT and CdTe crystals have significantly lower Te inclusions and defect densities than commercially available spectrometer grade crystals. The charge transport properties (electron and hole mobility-lifetime products, mutaue & mutauh) of various detectors have been evaluated by Hecht analysis. The detectors have been tested for spectral response using 59.5 and 662 keV gamma-ray sources. The CZT detectors with planar electrodes showed 2.6% FWHM at 662 keV. By adding a Frisch collar, the detectors' spectra improved significantly. The Frisch collar detectors proved to be very promising for assembling large-area arrays with excellent energy resolution at relatively low manufacturing cost.

We discuss the findings from our studies of the performance of commercial coplanar-grid CdZnTe detectors. The devices were investigated using a highly collimated X-ray beam available at Brookhaven's National Synchrotron Light Source, and by applying pulse-shape analysis to measure correlations between the signals read out from the devices. Although the operational principle of coplanar-grid (CPG) detectors is well known, we found some important new details that help to better clarify the performance limitations of this type of device. The correlation plots we present can also be used as diagnostic tools to characterize the behavior of the CPG devices and to help to improve the designs of electrodes. This work illustrates the typical limitations related to the geometry of the contacts in CPG devices and how material nonuniformities can amplify these problems.

The performance characteristics of Frisch-ring CdZnTe (CZT) detectors are described and compared with other types of CZT devices. The Frisch-ring detector is a bar-shaped CZT crystal with a geometrical aspect ratio of /spl sim/1:2. The side surfaces of the detector are coated with an insulating layer followed by a metal layer deposited directly upon the insulator. The simple design operates as a single-carrier device. Despite the simplicity of this approach, its performance depends on many factors that are still not fully understood. We describe results of testing several detectors fabricated from CZT material produced by different vendors and compare the results with numerical simulations of these devices.

In the past few years, significant progress has been achieved in the development of room-temperature semiconductor detectors, particularly those based on CdZnTe (CZT) crystals. Several types of electron-transport-only detectors have been developed: pixel, coplanar-grid, cross-strip, drift-strip, orthogonal coplanar strip, and virtual Frisch grid, many of which are now commercially available. Despite all these varieties in the detector designs, they have many common features and problems. This review summarizes the common detector design constraints and related factors limiting performance of CZT detectors: bulk and surface leakage currents, surface effects, properties of Schottky contacts and surface interfacial layers, charge sharing and loss in multielectrode devices, charge transport nonuniformities, and fluctuations in the pulse height for long-drift-length devices. We also describe unique capabilities at Brookhaven National Laboratory, Upton, NY, for CZT device characterization and recent progress utilizing these tools.

We evaluated the effect of high-temperature treatment of Cd0.9Zn0.1Te:In single crystals using Hall-effect measurements, medium- and high-temperature annealing under various deviations from stoichiometry, and infra-red (IR) transmission microscopy Annealing at ~730 K sharply increased the electrical conductivity (by ~1-2 orders-of-magnitude). Plots of the temperature- and cadmium-pressure dependences of the electrical conductivity, carrier concentration, and mobility were obtained. Treating previously annealed Cd-samples under a Te overpressure at 1070 K allowed us to restore their resistance to its initial high values. The main difference in comparing this material with CdTe was its lowered electron density. We explained our results within the framework of Kroger’s theory of quasi-chemical reactions between point defects in solids.

Frisch-ring CdZnTe detectors have demonstrated both good energy resolution