Application of CdTe for the NeXT mission

Abstract

Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) have been regarded as promising semiconductor materials for hard X-ray and γ -ray detection. The high-atomic number of the materials ( Z Cd = 48 , Z Te = 52 ) gives a high quantum efficiency in comparison with Si. The large band-gap energy ( E g = 1.5 eV ) allows to operate the detector at room temperature. Based on recent achievements in high-resolution CdTe detectors, in the technology of ASICs and in bump-bonding, we have proposed the novel hard X-ray and γ -ray detectors for the NeXT mission in Japan. The high-energy response of the super mirror onboard NeXT will enable us to perform the first sensitive imaging observations up to 80 keV. The focal plane detector, which combines a fully depleted X-ray CCD and a pixellated CdTe detector, will provide spectra and images in the wide energy range from 0.5 to 80 keV. In the soft γ -ray band up to ∼ 1 MeV , a narrow field-of-view Compton γ -ray telescope utilizing several tens of layers of thin Si or CdTe detector will provide precise spectra with much higher sensitivity than present instruments. The continuum sensitivity will reach several × 10 - 8 photons - 1 keV - 1 cm - 2 in the hard X-ray region and a few × 10 - 7 photons - 1 keV - 1 cm - 2 in the soft γ -ray region.