RESPONSE OF AMORPHOUS-SILICON P-I-N DETECTORS TO IONIZING PARTICLES

Prototypes of thin film p-i-n amorphous silicon detectors, having intrinsic layer thicknesses ranging from 3 to 18-mu-m, were designed and fabricated, and their response to protons of 1.3 to 11.6 MeV, and to alpha particles of 1.6 to 14.6 MeV was studied. The collection efficiency of the charges generated by a particle is found to decrease sharply with increasing d E/dx, for d E/dx values greater than 10 keV/mu-m. However, there exists a domain of oblique angles of incidence, relatively high applied biases and low d E/dx values over which the signal amplitude varies linearly with energy loss. Pulse shape studies show the signal to consist of a steep leading edge, attributed to prompt electron collection, and a slow component showing evidence of multiple-trapping transport of holes, which is a possible cause for incomplete collection of the generated charge at the maximum attainable field of 60 V/mu-m. Finally, all detectors give signal amplitudes compatible with a mean electron-hole pair creation energy of 3.4 to 4.4 eV in a-Si:H.