Direct processes in the energy deposition of protons in silicon
The low energy part of proton induced SBD spectra have higher number of counts than expected from p+Si reactions. This is the case for all proton incident angles but the effect increases when approaching grazing angles. The effect is shown to be mainly due to direct ionization (including straggling) by the protons. The energy deposition due to this process is first calculated using the chord length distribution model which assumes a constant LET value for the protons. This model can explain the main features of the spectra for grazing angles. It fails to produce the long tails found in all spectra which are shown to come from straggling. The direct ionization by the protons may cause SEU in devices with low critical charge.