Evaluation of pixellated, back-sided planar photodetectors for high-resolution imaging instrumentation

Future generations of solid-state high-energy gamma imaging cameras require pixellated semiconductor photodetectors with the greatest possible detection efficiency. In this paper, a new type of planar silicon PIN photodiode is presented, in which both p+p+ and n+n+ electrodes are located on the same side of the device. The design offers highly efficient optical coupling between the backside and scintillator, providing a fill factor of close to 100%. The performance of this detector is modelled using the ISE-TCAD simulator and its electrical and spectroscopic characteristics are experimentally investigated for the case of direct interaction of ionising radiation and also with an attached CsI(Tl) scintillator. The energy resolutions obtained at room temperature (21∘C) at 662 keV (scintillated) and 27 keV (direct) were 6.3% and 7.0% respectively, measured at full width at half maximum (FWHM). The new detector can be easily manufactured into arrays, for a variety of imaging (instrumentation) applications.