Spatially dependent response of thick and large area p-i-n diode for ASTRO-E hard X-ray detector

The ASTRO-E hard X-ray detector utilizes GSO(Gd/sub 2/SiO/sub 5/:Ce 0.5% mol)-BGO(Bi/sub 4/Ge/sub 3/O/sub 12/) well-type phoswich counters in compound-eye configuration to achieve an extremely low background level of about a few times 10/sup -5/ counts s/sup -1/ cm/sup -2/ keV/sup -1/. The GSO scintillators placed at the bottom of the BGO well observe photons in the energy range 30-600 keV. To cover the lower energy range of 10-60 keV, Si p-i-n diodes of 2 mm in thickness and 21.5/spl times/21.5 mm/sup 2/ in size were newly developed and placed in front of the GSO scintillators. The p-i-n diode exhibits complex spectral responses, including subpeak and low energy tail components. To examine the origin of these components, we measured the spatially resolved response of the p-i-n diode and confirmed that the subpeak and the low energy tail are related to the electrode structures and electric fields in the p-i-n diode, respectively.