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 defector utilizes GSO(Gd2SiO5:Ce 0.5% mol)-BGO(Bi4Ge 3O12) well-type phoswich counters [1] in compound-eye configuration to achi eve an extremely low background level of about a few times 10(-5) counts s( -1) cm(-2) keV(-1). The GSO scintillators placed at the bottom of the BGO w ell observe photons in the energy range 30-600 keV. To cover the lower ener gy range of 10-60 keV, silicon p-i-n diodes of 2 mm in thickness and 21.5 x 21.5 mm(2) in size were newly developed and placed in front of the GSO sci ntillators. The p-i-n diode exhibits complex spectral responses, including subpeak and low energy tail components. To examine the origin of these comp onents, we measured the spatially resolved response of the p-i-n diode and confirmed that the subpeak and the low energy tall are related to the elect rode structures. and electric, fields in the p-i-n. diode, respectively.