Electron trapping nonuniformity in high-pressure-Bridgman-grown CdZnTe

Abstract

Gamma-ray spectroscopy is a valuable tool of science and technology. Many applications for this tool are in need of a detector technology capable of achieving excellent energy resolution and efficient detection while operating at room temperature. Detectors based on the material cadmium zinc telluride (CdZnTe) could potentially meet this need if certain material deficiencies are addressed. The coplanar-grid as well as other electron-only detection techniques are effective in overcoming some of the material problems of CdZnTe and, consequently, have led to efficient gamma-ray detectors with good energy resolution while operating at room temperature. At the present time, the performance of these detectors is mainly limited by the degree of uniformity in electron generation and transport. Despite recent progress in the growth of CdZnTe material, small variations in these properties remain a barrier to the widespread success of such detectors. Alphaparticle response characterization of CdZnTe crystals fabricated into simple planar detectors provides an effective tool to accurately study such variations. We have used a finely collimated alpha source to produce two-dimensional maps of detector response. For a number of crystals, a clear correlation has been observed between their alpha response maps and the distribution of tellurium inclusions inside the crystals. An analysis of the induced charge signals indicates that regions of enhanced electron trapping are associated with the inclusions, and that these regions extend beyond the physical size of the inclusions. Such regions introduce non-uniform electron trapping in the material that then degrades the spectroscopic performance of the material as a gamma-ray detector.2

Drift mobility and mobility-lifetime products in CdTe:Cl grown by the travelling heater method

“…No evidence was observed for extended trapping sites in this sample. Such trapping sites have been observed in CdZnTe, caused by the presence of tellurium inclusions with diameters in the range 1-10 m [12]. Using infrared microscopy, tellurium inclusions have also been observed around the wafer edges of THM-grown CdTe [13], [14], and further measurements are required to identify the nature and extent of charge trapping around such inclusions.…”

CdTe/CZT under high flux irradiation

“…For inclusions of a size of more than 100µm, this behaviour is known [42][43][44]. In the experiment, parts of one detector with higher and lower concentration of Te-inclusions were compared (figure 8a).…”

Ion Beam Induced Charge Studies of CdZnTe Grown by Modified Vertical Bridgman Method

“…Spatial distributions of the transport properties of CdZnTe have also been demonstrated using focused X-rays [13], [14] and collimated alpha particles [15], [16]. These measurements have shown evidence for the localized effect of crystal defects, such as Tellurium Inclusions, and their associated trapping levels on the charge transport properties of CdZnTe.…”