Thick CZT detectors for spaceborne x-ray astronomy

Abstract

Cadmium Zinc Telluride (CZT) detectors are having a major impact on the field of hard X-ray astronomy. Without the need for cryogenic cooling they achieve good spatial and energy resolutions over the broad energy range from 10 keV to ∼600 keV. In this paper, we briefly review the historical development of detectors used in Xray astronomy. Subsequently, we present an evaluation of CZT detectors from the company Imarad. The standard 2×2×0.5 cm detectors, contacted with 8×8 In pixels and an In cathode, exhibit FWHM energy resolutions of 7 keV at 59 keV, and 10 keV at 662 keV. A direct measurement of the 662 keV photopeak efficiency gives 67%. We have started a detailed study of the performance of Imarad detectors depending on surface preparation, contact materials, contact deposition, post-deposition detector annealing, and detector passivation techniques. We present first results from contacting detectors with Cr, Ag, Au, and Pt.

Fabrication and test of pixelated CZT detectors with different pixel pitches and thicknesses

“…Results obtained with a 1 cm thick 64-pixel detector (2.5 mm pixel pitch) Fig. 4(a) shows the results from a test of a 1×2×2 cm 3 CZT detector from the company eV-Products with a 662 keV 137 Cs source (-1800 V bias voltage, 1 µs shaping time). The detector was contacted with 64 pixels, but only 60 of the 64 pixels were connected to the readout system, as the detector surface of the remaining 4 pixels will be used in future to connect a grid between the pixels to a steering voltage.…”

“…The EXIST (Energetic X-ray Imaging Survey Telescope) mission is a proposed all sky survey hard X-ray survey telescope that would use ~14,000 CZT detectors in a coded mask imager with a detector area of 5.5 m 2 [6]. The EXIST mission would use 0.5×2×2 cm 3 CZT detectors each read out with 1024 pixels at a pitch of 0.6 mm. An example of a particle physics experiment is the neutrinoless double beta decay experiment COBRA [7].…”

“…c) Energy spectrum of 0.5×2×2 cm3 Orbotech CZT detector contacted with 8×8 pixel (cathode bias: -1100 V).…”

Simulation, modeling, and crystal growth of Cd0.9Zn0.1Te for nuclear spectrometers

“…The energy required for generating one electron-hole pair in CZT (;5 eV) is much less than that required for scintillation crystals coupled to photomultiplier tubes (;50 eV), resulting in better energy resolution. [6][7][8][9] (Received October 17, 2005; accepted December 14,2005) Although tremendous efforts have been made to grow large, high-quality CZT crystals, the production of CZT, dominated by the high-pressure Bridgman method, suffers from low yields and small device sizes. 5 Due to these advantages, CZT has been the material of choice for x-and g-ray detectors for medical imaging, infrared focal plane array, national security, environmental monitoring, and space astronomy.…”

Direct comparison of the performance of CZT detectors contacted with various metals

“…That is the reason that lead us to undertake a detailed study of the influence that different contact materials might have on detector performance. Compared to our earlier work, 6 we describe here a more direct comparison between different contact materials by using the same detectors with different cathode and/or anode contacts. First we present an overview about deposition procedures used and our readout electronics.…”