Temperature Study of CdZnTe Coplanar-Grid Detectors

The coplanar-grid (CPG) and other electron-only detection techniques have made possible the use of CdZnTe-based detectors for gamma-ray spectroscopy when high efficiency, good energy resolution, and near room temperature operation are required. Despite the demonstrated potential of the technologies, widespread use remains hampered in part by the limited availability of the highly uniform CdZnTe material required for high-resolution spectroscopy. However, it has been recently shown that mild cooling of CdZnTe CPG detectors can result in a significant improvement in the energy resolution of the detectors thereby allowing a wider range of material to be used for high-resolution applications. In this paper, we show that improved spectroscopic performance can consistently be achieved through a combination of detector cooling and increased detector bias. Energy resolutions of about 1% FWHM at 662 keV for detector volumes up to 2.3 cm³ have been obtained at -20degC. With the electronic noise subtracted, this amounts to an intrinsic resolution of 0.8%. We also show that further cooling of the detectors to -30degC leads to field polarization and a loss of spectroscopic performance