DETECTION OF CHARGED-PARTICLES AND X-RAYS BY SCINTILLATOR LAYERS COUPLED TO AMORPHOUS-SILICON PHOTODIODE ARRAYS

Hydrogenated amorphous silicon (a-Si:H) p-i-n diodes with transparent metallic contacts are shown to be suitable for detecting charged parti cles, electrons, and X-rays. When coupled to a suitable scintillator u sing CsI(Tl) as the scintillator we show a capability to detect minimu m ionizing particles with SIN similar to 20. We demonstrate such an ar rangement by operating a p-i-n diode in photovolaic mode (reverse bias ). Moreover, we show that a p-i-n diode can also work as a photoconduc tor under forward bias and produces a gain yield of 3-8 higher light s ensitivity for shaping times of 1 mu s n-i-n devices have similar opti cal gain as the p-i-n photoconductor for short integrating times (<10 mu S). However, n-i-n devices exhibit much higher gain for a long term integration (10 ms) than the p-i-n ones. High sensitivity photosensor s are very desirable for X-ray medical imaging because radiation expos ure dose can be reduced significantly. The scintillator CsI layers we made have higher spatial resolution than the Kodak commercial scintill ator screens due to their internal columnar structure which can collim ate the scintillator light. Evaporated CsI layers are shown to be more resistant to radiation damage than the crystalline bulk CsI(Tl).