Recent developments in CdTe and CdZnTe detectors

Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) has been regarded as a promising semiconductor material for hard X-ray and gamma-ray detection. The high atomic number of the materials (Z-Cd=48, Z-Te=52) gives a high quantum efficiency in comparison with Si. A large band-gap energy (Eg~1.5 eV) allows us to operate the detector at room temperature. However, a considerable amount of charge loss in these detectors produces a reduced energy resolution. This problem arises due to the low mobility and short lifetime of holes. Recently, significant improvements have been achieved to improve the spectral properties based on the advances in the production of crystals and in the design of electrode. In this overview talk, we summarize (1) advantages and disadvantages of CdTe and CdZnTe semiconductors, (2) a technique to improve the energy resolution and photopeak efficiencies at high gamma-ray energy, and (3) recent achievements of segmented (strip and pixel) CdTe and CdZnTe detectors. The application of these imaging detectors in future hard X-ray and gamma-ray astronomy missions is briefly discussed