Development of the semi conductor imaging spectrometer for hard X-ray and gamma-ray observations

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We have been working on the development of high energy resolution Cadmium Teluride (CdTe) diode detector and its application to the gamma-ray imaging detectors. In this research, we developed a large CdTe diode detector with an area of 2.15 cm by 2.15 cm. It shows very good uniformity throughout the detector area. The energy resolution of 2.7 keV (FWHM) has been achieved. In order for the application in space, we did a vibration test, a radiation test and a balloon experiment. According to the results of these experiments we have proved that CdTe diode can be used in space application. A stack detector with several 10 layers of large CdTe diode was built and tested to prove the performance for the gamma-ray detection. Prototype 1024 pixel detectors with the pixel size of 200 micron by 200 micron and 1 mm by 1 mm are also constructed. From theoretical side, we studied polarization phenomena we often experienced from the CdTe diode in room temperature operation. We found that the charge accumulation due to ionization of deep acceptor is the reason. This explains well about temperature and bias voltage dependence. The characterization of CdZnTe to be used in the Swift mission is another topics. We have developed new method to derive mobility and life time products by fitting energy spectra. This method is adopted by the calibration process of the swift mission.