Signal formation in a-Si:H particle detectors

The response of a hydrogenated amorphous silicon thin film p-i-n diode to protons is presented as a function of the applied bias. A typical pulse shape is also presented. These data are explained on the basis of a model whose main features are fast (<5 ns) electron collection and slow (a few microseconds) hole collection due to multiple trapping transport through the shallow gap states. The overall charge normalization yields a mean pair creation energy in /sub p/ of 3.4-4.4 eV, comparable to 3.63 eV in crystalline silicon despite the larger 1.7-eV gap. To explain this result, a microscopic Monte Carlo calculation, taking into account the actual density of states in a-Si:H, is used to study the energy sharing between ionization and phonon production during hot carrier thermalization. This simulation yields a value of 4.3 eV for in /sub p/.<
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