Abstract"Electron-only" detection techniques such as the coplanargrid method are effective in overcoming some of the charge transport problems of CdZnTe and, consequently, have led to large-volume gamma-ray detectors with good energy resolution while operating at room temperature. A requirement for the success of these techniques is uniformity in electron generation and transport.Once large inhomogeneities in these properties caused by grain boundaries and other large-scale crystal defects are eliminated through simple material screening techniques, small variations remain and limit the gamma-ray energy resolution. In this paper we present the results from our characterization and analysis of these nonuniformities in commercially available CdZnTe, and we establish the relationship between the nonuniformities and the ultimate coplanar-grid gamma-ray detector performance through experimental measurements.
Abstract--Noise measurements on CdZnTe detectors show that the main sources of detector-related noise are shot noise due to bulk leakage current and 1/f noise due to the detector surfaces. The magnitude of surface leakage current appears to have little or no effect on the detector noise. Measurements on guard-ring devices fabricated using gold-evaporated contacts show that the contacts behave as Schottky barriers, and the bulk current at typical operating voltages is likely dependent on the contact properties rather than directly on the material's bulk resistivity. This also suggests that the level of shot noise is affected by the detector contacts and not necessarily by the material's bulk resistivity. A significant reduction in the noise of coplanar-grid detectors has been obtained using a modified contact fabrication process.
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