Cd(Zn)Te Detectors for Hard X-Ray and Gamma-Ray Astronomy

The energy range of hard X-rays and gamma-rays is dominated by non-thermal emissions. Physical processes such as particle acceleration, accretion, and nucleosynthesis are observable and are at play in the most violent phenomena of the Universe (e.g., supernovae, relativistic jets, gamma ray bursts). Despite the importance of information from hard X-rays and gamma-rays for the understanding of the enigmatic compact objects, this science suffers from instrumental limitations in the development of space systems with good detection efficiency. Complementing the success of high resistivity silicon and high purity germanium, the need for new high density and high atomic number (Z) materials has quickly become crucial. While CdTe-based material has been identified as a good candidate since the 1970s, producing good detectors from the crystal growth to the implementation in a detection system is complex. High-energy astrophysics in space instruments is very demanding in terms of crystal quality and uniformity compared to other industrial applications (medical imaging, homeland security, nuclear safety). Charge carrier mobility and lifetime must be maximized to allow full charge collection; high resistivity allows low leakage current at room temperature or with moderate cooling. Both parameters are key factors for the spectral performance of detectors. Advances in device imaging capabilities are also crucial to this domain of astrophysics even though most sources are point sources; this allows the use of hard X-ray focusing optics to improve telescope sensitivity by several orders of magnitude and this additionally provides polarimetric capability. The imaging capability obviously benefits the observation of extended sources, such as supernova remnants and closer to us, solar flares. We review here the key parameters to produce, design, and implement a detection system based on Cd(Zn)Te detectors, in the prospect of exploiting the light information from the astrophysics sources in the best possible way by providing optimal detection efficiency, spectral, imaging, or polarimetric performances. Combining these capabilities in a single system is possible, which is a great advantage of such material, given some design trade-offs. The illustrations with realized space instruments are the best examples of possible implementations.