Near room temperature X-ray and γ-ray spectroscopic detectors for future space experiments

New generation Cadmium Telluride (CZT and CdTe) solid-state detectors can provide high quantum efficiency with reasonably good energy resolution and can operate at near room temperature; a unique advantage for space experiments. We present here results of our study of small diode detectors as well as large area pixel detectors. Our study is aimed at developing near room temperature hard X-ray spectroscopy detectors for ASTROSAT and other future Indian space science missions. We have studied a Si-PIN detector in the energy range 5-60 keV and CZT and CdTe Schottky diode detectors in the energy region 10-1330keV. Our results suggest that the energy resolution is limited by the thermal/electronic noise in the low-energy region (<= 60keV) while it is affected by the charge transport properties of the detector in the higher energy region (>= 100keV). We have studied large area (64cm(2)) CZT pixel detectors with pixel size close to the small CZT detector. We have studied individual pixels as well as CZT detector as a whole (summed over all the 1024 pixels). The CZT pixel detectors are single carrier detectors with peaking time <= 1 vs. The energy resolution behaviour of the large area CZT detector is similar to that of small diode detectors in the low-energy region. The change in operating temperature from room temperature similar to 20 to similar to 70 degrees C drastically affects both the energy resolution as well as the peak area due to a sharp rise in the thermal noise. These results suggest that the cooling of detector system will provide better energy resolution as well as detection efficiency. Our results also show that the crystal uniformity is another important issue in the case of large area CZT pixel detectors. (c) 2005 Elsevier B.V. All rights reserved.