Detector and Mission Development
Development of X-ray and Gamma-Ray Detectors
Sponsored by NASA, we develop Cadmium Zinc Telluride (CZT) detectors
that detect photons in the 10 keV to several MeV energy range.
CZT is a II-VI large bandgap compound semiconductor.
Owing to its high atomic number of Z~50 it achieves an extremely high photopeak efficiency.
The large bandgap of about 1.6 eV makes it possible to achieve excellent energy
resolutions, operating the detectors at room temperature.
Our main focus is on using CZT material
from the company IMARAD.
Starting with 2cm x 2cm large and 0.5cm-1cm thick CZT substrates, we fabricate detectors
in a dedicated class-100 cleanroom, equipped with a wet-bench for bromine etching,
full photo-lithography equipment, and an electron beam vapor deposition system.
The group combines unique detector fabrication capabilities with comprehensive
substrate and detector characterisation and with very detailed device modeling.
The work aims at the development of low-cost CZT detectors with excellent spatial
resolution (< 1mm) and energy resolution (<2%), and extremely high photo-peak
efficiency (>80%).
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| IMARAD CZT crystals before contact deposition. |
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| IMARAD CZT crystal after deposition of chromium contacts in our lab. |
Design Studies Related to the EXIST Hard X-ray All Sky-Survey Telescope
In collaboration with scientists from Harvard and other institutions, we work on the concept of the satellite borne black hole finder telescope EXIST. The EXIST telescope will use an area of about 8 square meter of CZT detectors to detect X-rays in the energy range from 10 keV to 600 keV. At these energies, photons suffer little absorption by cosmic dust. The telescope will make it possible to survey the vast population of supermassive black holes that lure at the centers of most galaxies in the local as well as in the very early universe. We investigate the possibility to extend the capabilities of the instrument by using a CsI anti-coincidence shield of 35 square meter surface area to extend the energy coverage of the CZT detectors towards higher energies. The shield could be used to determine the energy spectra of Gamma-Ray Bursts up to energies of 10 MeV. Our mission design studies are based on the GEANT-4 code to simulate particle interactions and on the DETECT2000 code to simulate the transport optical photons through the scintillator.
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| "Geant 4" simulation of a high energy gamma-ray striking the EXIST detector. The white lines are the CsI shields and yellow are the CZT detectors. |
Detector Development for Medical and Homeland Security Applications
The Washington University group develops room temperature semiconductor detectors for PET imagers, and for homeland security applications.