SIGNAL FORMATION IN A-SI-H PARTICLE DETECTORS

The response of an 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 understood on the basis of a model whose main features are fast (< 5 nsec) electron collection and slow (few mu-sec) hole collection due to multiple trapping transport through the shallow gap states. The overall charge normalization yields a mean pair creation energy epsilon-p of 3.4-4.4 eV, comparable to 3.63 eV in crystalline Silicon despite the larger 1.7 eV gap. To understand 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 epsilon-p.