Design of high-performance CdZnTe quasi-hemispherical gamma-ray CAPture plus detectors

Abstract

We report on the material selection, testing and fabrication technology development of high performance CdZnTe quasihemispherical CAPture TM Plus radiation detectors. Quasi-hemispherical CdZnTe detectors offer a cost effective alternative to other single-polarity (electron-only) detector configurations such as co-planar grid, pixilated or Frisch ring CdZnTe detectors with comparable energy resolution both in the high (>500 keV) and low energy range (<500 keV). The performance of the quasi-hemispherical detectors is controlled by charge transport properties of the CdZnTe crystals, quality of device fabrication and device integration. Similarly to other single-polarity CdZnTe device configurations the charge transport uniformity of the CdZnTe crystals is critical for achieving high energy resolution. We realized this by carefully selecting high electron transport CdZnTe crystals (μτ e greater than or equal to 6.0×10 -3 cm 2 /V) with uniform distribution of structural defects. Infra-red microscopy was employed for structural defect mapping of the crystals. Low sub-surface damage state-of-the art multi- and single-wire saw technologies were used to slice and dice the single crystal detector elements out of the CdZnTe ingots. Dimensional control of the crystals was preserved throughout chemical etching and chemo-mechanical polishing by minimizing material removal. Device fabrication employing state-of-the art photolithography, electrode deposition and surface passivation enabled the application of bias voltages as high as 5000 V/cm on the devices. With carefully selected high uniformity CdZnTe crystals and low-noise preamplifier energy resolution better than 4.8% FWHM at 81 keV, 3.0% FWHM at 122 keV and 1.5% FWHM at 662 keV was achieved on 10×10×5 mm 3 quasi-hemispherical detectors.