Spatially dependent response of thick and large area PIN diode developed for ASTRO-E hard X-ray detector

The ASTRO-E Hard X-ray Detector utilizes GSO/BGO 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, silicon PIN 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 PIN diode exhibits complex spectral responses, including subpeak and low energy tail components. To examine the origin of these components, we measured spatially-resolved response of the PIN diode, and confirmed that the subpeak and the low energy tail are related to the electrode structures and electric fields in the PIN diode, respectively.