The effect of the angle of incidence on proton induced single events in devices - A critical assessment by modeling

The effect of the angle of incidence on the proton induced single events in devices with finite dimensions is studied using a modified Monte Carlo model. The physical reasons for the existence or the absence of an anisotropy of the single event occurrence (with respect to the proton angle of incidence) are highlighted for the first time. Several different cases are found: (1) A significant anisotropy is predicted for devices with small lateral dimensions, a smaller sensitive layer thickness, and a large critical energy. The origin of this angular dependence is shown to be the contribution of the highly anisotropic medium mass fragments which is dominant for these conditions. (2) Published experimental data indicate only a small anisotropy in practical devices, which are characterized by a small critical deposited energy needed for SEU. It is shown that for these devices, most of the charge is created by the heavy mass fragments, which are isotropic. (3) In surface barrier detectors (SBDs) which have large lateral dimensions the effect of the isotropic light mass fragments takes over and the anisotropy for proton events is small even for large critical energies and a small sensitive layer thickness. The conclusion of the present work is that the single event rate in space can be evaluated by the normal incidence cross sections for all devices which have a significant sensitivity for proton induced events.