Experimental evaluation and simulation of multi-pixel cadmium-zinc-telluride hard-X-ray detectors

This dissertation describes the evaluation of many-pixel Cadmium-Zinc-Telluride (CdZnTe) hard-X-ray detectors for future use with the High Energy Replicated Optics (HERO) telescope being developed at Marshall Space Flight Center. The detector requirements for the HERO application are good energy resolution (sufficient to resolve cyclotron features and nuclear lines), spatial resolution of ∼200 mum, minimal charge loss of absorbed X rays, and minimal sensitivity to the background environment. This research concentrates on assessing the suitability of these detectors for the focus of HERO, and includes the development of a simulation of the physics involved in an X-ray-detector interaction, a study of the intrinsic material properties, measurements with prototype detectors such as the energy and spatial resolution, charge loss, and X-ray background reduction through 3-dimensional depth sensing.; Two types of detectors were available for evaluation. The first type includes 1-mm and 2-mm thick 4 x 4 pixel arrays, developed by Metorex Inc. and Baltic Scientific Instruments. The pixel size is 650 mum with inter-pixel gap of 100 mum. Each of the 16 pixels is wired to a charge sensitive preamplifier and then fed to external electronics. The second detector type includes 1-mm and 2-mm thick 16 x 16 pixel arrays with pixel size of 250 mum square and 50 mum inter-pixel gap. Each array is bonded to an Application Specific Integrated Circuit (ASIC) readout chip, developed by Rutherford Appleton Laboratory (RAL) and fabricated by Metorex Inc.; The best energy resolution for both detector types is ∼2% at 60 keV. However, the energy resolution across the 16 x 16 pixel arrays varies dramatically, possibly due to the bonding technique used between the CdZnTe crystal and the ASIC. Position interpolation through charge sharing improves spatial resolution on the 16 x 16 pixel arrays from 300 mum to ∼250 mum. Minimal charge loss was measured for the 16 x 16 pixel arrays. Preliminary studies of 3-dimensional depth sensing on the 4 x 4, 2-mm-thick pixel array show promising results. These measurements, combined with simulation, show that many-pixel CdZnTe pixel arrays can make ideal focal plane detectors for the HERO telescope.