Abstract
A simple physical model explains all the characteristics of the newly discovered funnelling phenomenon. An alpha strike results in significant field in the quasi-neutral regions to a depth that is equal to 1 + µ _{n} /µ _{p} times the depletion region width of an n+/p junction. This and the predicted current waveform agree with experiments and simulation results. The model also predicts the effects of the angle of alpha incidence, and that p+/n junctions should exhibit weaker funnelling phenomenon.